PERLGUTS(1)      Perl Programmers Reference Guide     PERLGUTS(1)

NNAAMMEE
       perlguts - Perl's Internal Functions

DDEESSCCRRIIPPTTIIOONN
       This document attempts to describe some of the internal
       functions of the Perl executable.  It is far from complete
       and probably contains many errors.  Please refer any
       questions or comments to the author below.

VVaarriiaabblleess
       DDaattaattyyppeess

       Perl has three typedefs that handle Perl's three main data
       types:

           SV  Scalar Value
           AV  Array Value
           HV  Hash Value

       Each typedef has specific routines that manipulate the
       various data types.

       WWhhaatt iiss aann """"IIVV""""??

       Perl uses a special typedef IV which is a simple integer
       type that is guaranteed to be large enough to hold a
       pointer (as well as an integer).

       Perl also uses two special typedefs, I32 and I16, which
       will always be at least 32-bits and 16-bits long,
       respectively.

       WWoorrkkiinngg wwiitthh SSVVss

       An SV can be created and loaded with one command.  There
       are four types of values that can be loaded: an integer
       value (IV), a double (NV), a string, (PV), and another
       scalar (SV).

       The six routines are:

           SV*  newSViv(IV);
           SV*  newSVnv(double);
           SV*  newSVpv(char*, int);
           SV*  newSVpvn(char*, int);
           SV*  newSVpvf(const char*, ...);
           SV*  newSVsv(SV*);

       To change the value of an *already-existing* SV, there are
       seven routines:

           void  sv_setiv(SV*, IV);
           void  sv_setuv(SV*, UV);
           void  sv_setnv(SV*, double);
           void  sv_setpv(SV*, const char*);
           void  sv_setpvn(SV*, const char*, int)
           void  sv_setpvf(SV*, const char*, ...);
           void  sv_setpvfn(SV*, const char*, STRLEN, va_list *, SV **, I32, bool);
           void  sv_setsv(SV*, SV*);

       Notice that you can choose to specify the length of the
       string to be assigned by using sv_setpvn, newSVpvn, or
       newSVpv, or you may allow Perl to calculate the length by
       using sv_setpv or by specifying 0 as the second argument
       to newSVpv.  Be warned, though, that Perl will determine
       the string's length by using strlen, which depends on the
       string terminating with a NUL character.

       The arguments of sv_setpvf are processed like sprintf, and
       the formatted output becomes the value.

       sv_setpvfn is an analogue of vsprintf, but it allows you
       to specify either a pointer to a variable argument list or
       the address and length of an array of SVs.  The last
       argument points to a boolean; on return, if that boolean
       is true, then locale-specific information has been used to
       format the string, and the string's contents are therefore
       untrustworthy (see the perlsec manpage).  This pointer may
       be NULL if that information is not important.  Note that
       this function requires you to specify the length of the
       format.

       The sv_set*() functions are not generic enough to operate
       on values that have "magic".  See the section on Magic
       Virtual Tables later in this document.

       All SVs that contain strings should be terminated with a
       NUL character.  If it is not NUL-terminated there is a
       risk of core dumps and corruptions from code which passes
       the string to C functions or system calls which expect a
       NUL-terminated string.  Perl's own functions typically add
       a trailing NUL for this reason.  Nevertheless, you should
       be very careful when you pass a string stored in an SV to
       a C function or system call.

       To access the actual value that an SV points to, you can
       use the macros:

           SvIV(SV*)
           SvNV(SV*)
           SvPV(SV*, STRLEN len)

       which will automatically coerce the actual scalar type
       into an IV, double, or string.

       In the SvPV macro, the length of the string returned is
       placed into the variable len (this is a macro, so you do
       not use &len).  If you do not care what the length of the
       data is, use the global variable PL_na or a local variable
       of type STRLEN. However using PL_na can be quite
       inefficient because PL_na must be accessed in thread-local
       storage in threaded Perl.  In any case, remember that Perl
       allows arbitrary strings of data that may both contain
       NULs and might not be terminated by a NUL.

       Also remember that C doesn't allow you to safely say
       foo(SvPV(s, len), len);. It might work with your compiler,
       but it won't work for everyone.  Break this sort of
       statement up into separate assignments:

               STRLEN len;
               char * ptr;
               ptr = SvPV(len);
               foo(ptr, len);

       If you want to know if the scalar value is TRUE, you can
       use:

           SvTRUE(SV*)

       Although Perl will automatically grow strings for you, if
       you need to force Perl to allocate more memory for your
       SV, you can use the macro

           SvGROW(SV*, STRLEN newlen)

       which will determine if more memory needs to be allocated.
       If so, it will call the function sv_grow.  Note that
       SvGROW can only increase, not decrease, the allocated
       memory of an SV and that it does not automatically add a
       byte for the a trailing NUL (perl's own string functions
       typically do SvGROW(sv, len + 1)).

       If you have an SV and want to know what kind of data Perl
       thinks is stored in it, you can use the following macros
       to check the type of SV you have.

           SvIOK(SV*)
           SvNOK(SV*)
           SvPOK(SV*)

       You can get and set the current length of the string
       stored in an SV with the following macros:

           SvCUR(SV*)
           SvCUR_set(SV*, I32 val)

       You can also get a pointer to the end of the string stored
       in the SV with the macro:

           SvEND(SV*)

       But note that these last three macros are valid only if
       SvPOK() is true.

       If you want to append something to the end of string
       stored in an SV*, you can use the following functions:

           void  sv_catpv(SV*, char*);
           void  sv_catpvn(SV*, char*, STRLEN);
           void  sv_catpvf(SV*, const char*, ...);
           void  sv_catpvfn(SV*, const char*, STRLEN, va_list *, SV **, I32, bool);
           void  sv_catsv(SV*, SV*);

       The first function calculates the length of the string to
       be appended by using strlen.  In the second, you specify
       the length of the string yourself.  The third function
       processes its arguments like sprintf and appends the
       formatted output.  The fourth function works like
       vsprintf.  You can specify the address and length of an
       array of SVs instead of the va_list argument. The fifth
       function extends the string stored in the first SV with
       the string stored in the second SV.  It also forces the
       second SV to be interpreted as a string.

       The sv_cat*() functions are not generic enough to operate
       on values that have "magic".  See the section on Magic
       Virtual Tables later in this document.

       If you know the name of a scalar variable, you can get a
       pointer to its SV by using the following:

           SV*  perl_get_sv("package::varname", FALSE);

       This returns NULL if the variable does not exist.

       If you want to know if this variable (or any other SV) is
       actually defined, you can call:

           SvOK(SV*)

       The scalar undef value is stored in an SV instance called
       PL_sv_undef.  Its address can be used whenever an SV* is
       needed.

       There are also the two values PL_sv_yes and PL_sv_no,
       which contain Boolean TRUE and FALSE values, respectively.
       Like PL_sv_undef, their addresses can be used whenever an
       SV* is needed.

       Do not be fooled into thinking that (SV *) 0 is the same
       as &PL_sv_undef.  Take this code:

           SV* sv = (SV*) 0;
           if (I-am-to-return-a-real-value) {
                   sv = sv_2mortal(newSViv(42));
           }
           sv_setsv(ST(0), sv);

       This code tries to return a new SV (which contains the
       value 42) if it should return a real value, or undef
       otherwise.  Instead it has returned a NULL pointer which,
       somewhere down the line, will cause a segmentation
       violation, bus error, or just weird results.  Change the
       zero to &PL_sv_undef in the first line and all will be
       well.

       To free an SV that you've created, call SvREFCNT_dec(SV*).
       Normally this call is not necessary (see the section on
       Reference Counts and Mortality).

       WWhhaatt''ss RReeaallllyy SSttoorreedd iinn aann SSVV??

       Recall that the usual method of determining the type of
       scalar you have is to use Sv*OK macros.  Because a scalar
       can be both a number and a string, usually these macros
       will always return TRUE and calling the Sv*V macros will
       do the appropriate conversion of string to integer/double
       or integer/double to string.

       If you really need to know if you have an integer, double,
       or string pointer in an SV, you can use the following
       three macros instead:

           SvIOKp(SV*)
           SvNOKp(SV*)
           SvPOKp(SV*)

       These will tell you if you truly have an integer, double,
       or string pointer stored in your SV.  The "p" stands for
       private.

       In general, though, it's best to use the Sv*V macros.

       WWoorrkkiinngg wwiitthh AAVVss

       There are two ways to create and load an AV.  The first
       method creates an empty AV:

           AV*  newAV();

       The second method both creates the AV and initially
       populates it with SVs:

           AV*  av_make(I32 num, SV **ptr);

       The second argument points to an array containing num
       SV*'s.  Once the AV has been created, the SVs can be
       destroyed, if so desired.

       Once the AV has been created, the following operations are
       possible on AVs:

           void  av_push(AV*, SV*);
           SV*   av_pop(AV*);
           SV*   av_shift(AV*);
           void  av_unshift(AV*, I32 num);

       These should be familiar operations, with the exception of
       av_unshift.  This routine adds num elements at the front
       of the array with the undef value.  You must then use
       av_store (described below) to assign values to these new
       elements.

       Here are some other functions:

           I32   av_len(AV*);
           SV**  av_fetch(AV*, I32 key, I32 lval);
           SV**  av_store(AV*, I32 key, SV* val);

       The av_len function returns the highest index value in
       array (just like $#array in Perl).  If the array is empty,
       -1 is returned.  The av_fetch function returns the value
       at index key, but if lval is non-zero, then av_fetch will
       store an undef value at that index.  The av_store function
       stores the value val at index key, and does not increment
       the reference count of val.  Thus the caller is
       responsible for taking care of that, and if av_store
       returns NULL, the caller will have to decrement the
       reference count to avoid a memory leak.  Note that
       av_fetch and av_store both return SV**'s, not SV*'s as
       their return value.

           void  av_clear(AV*);
           void  av_undef(AV*);
           void  av_extend(AV*, I32 key);

       The av_clear function deletes all the elements in the AV*
       array, but does not actually delete the array itself.  The
       av_undef function will delete all the elements in the
       array plus the array itself.  The av_extend function
       extends the array so that it contains at least key+1
       elements.  If key+1 is less than the currently allocated
       length of the array, then nothing is done.

       If you know the name of an array variable, you can get a
       pointer to its AV by using the following:

           AV*  perl_get_av("package::varname", FALSE);

       This returns NULL if the variable does not exist.

       See the section on Understanding the Magic of Tied Hashes
       and Arrays for more information on how to use the array
       access functions on tied arrays.

       WWoorrkkiinngg wwiitthh HHVVss

       To create an HV, you use the following routine:

           HV*  newHV();

       Once the HV has been created, the following operations are
       possible on HVs:

           SV**  hv_store(HV*, char* key, U32 klen, SV* val, U32 hash);
           SV**  hv_fetch(HV*, char* key, U32 klen, I32 lval);

       The klen parameter is the length of the key being passed
       in (Note that you cannot pass 0 in as a value of klen to
       tell Perl to measure the length of the key).  The val
       argument contains the SV pointer to the scalar being
       stored, and hash is the precomputed hash value (zero if
       you want hv_store to calculate it for you).  The lval
       parameter indicates whether this fetch is actually a part
       of a store operation, in which case a new undefined value
       will be added to the HV with the supplied key and hv_fetch
       will return as if the value had already existed.

       Remember that hv_store and hv_fetch return SV**'s and not
       just SV*.  To access the scalar value, you must first
       dereference the return value.  However, you should check
       to make sure that the return value is not NULL before
       dereferencing it.

       These two functions check if a hash table entry exists,
       and deletes it.

           bool  hv_exists(HV*, char* key, U32 klen);
           SV*   hv_delete(HV*, char* key, U32 klen, I32 flags);

       If flags does not include the G_DISCARD flag then
       hv_delete will create and return a mortal copy of the
       deleted value.

       And more miscellaneous functions:

           void   hv_clear(HV*);
           void   hv_undef(HV*);

       Like their AV counterparts, hv_clear deletes all the
       entries in the hash table but does not actually delete the
       hash table.  The hv_undef deletes both the entries and the
       hash table itself.

       Perl keeps the actual data in linked list of structures
       with a typedef of HE.  These contain the actual key and
       value pointers (plus extra administrative overhead).  The
       key is a string pointer; the value is an SV*.  However,
       once you have an HE*, to get the actual key and value, use
       the routines specified below.

           I32    hv_iterinit(HV*);
                   /* Prepares starting point to traverse hash table */
           HE*    hv_iternext(HV*);
                   /* Get the next entry, and return a pointer to a
                      structure that has both the key and value */
           char*  hv_iterkey(HE* entry, I32* retlen);
                   /* Get the key from an HE structure and also return
                      the length of the key string */
           SV*    hv_iterval(HV*, HE* entry);
                   /* Return a SV pointer to the value of the HE
                      structure */
           SV*    hv_iternextsv(HV*, char** key, I32* retlen);
                   /* This convenience routine combines hv_iternext,
                      hv_iterkey, and hv_iterval.  The key and retlen
                      arguments are return values for the key and its
                      length.  The value is returned in the SV* argument */

       If you know the name of a hash variable, you can get a
       pointer to its HV by using the following:

           HV*  perl_get_hv("package::varname", FALSE);

       This returns NULL if the variable does not exist.

       The hash algorithm is defined in the PERL_HASH(hash, key,
       klen) macro:

           hash = 0;
           while (klen--)
               hash = (hash * 33) + *key++;

       See the section on Understanding the Magic of Tied Hashes
       and Arrays for more information on how to use the hash
       access functions on tied hashes.

       HHaasshh AAPPII EExxtteennssiioonnss

       Beginning with version 5.004, the following functions are
       also supported:

           HE*     hv_fetch_ent  (HV* tb, SV* key, I32 lval, U32 hash);
           HE*     hv_store_ent  (HV* tb, SV* key, SV* val, U32 hash);

           bool    hv_exists_ent (HV* tb, SV* key, U32 hash);
           SV*     hv_delete_ent (HV* tb, SV* key, I32 flags, U32 hash);

           SV*     hv_iterkeysv  (HE* entry);

       Note that these functions take SV* keys, which simplifies
       writing of extension code that deals with hash structures.
       These functions also allow passing of SV* keys to tie
       functions without forcing you to stringify the keys
       (unlike the previous set of functions).

       They also return and accept whole hash entries (HE*),
       making their use more efficient (since the hash number for
       a particular string doesn't have to be recomputed every
       time).  See the section on API LISTING later in this
       document for detailed descriptions.

       The following macros must always be used to access the
       contents of hash entries.  Note that the arguments to
       these macros must be simple variables, since they may get
       evaluated more than once.  See the section on API LISTING
       later in this document for detailed descriptions of these
       macros.

           HePV(HE* he, STRLEN len)
           HeVAL(HE* he)
           HeHASH(HE* he)
           HeSVKEY(HE* he)
           HeSVKEY_force(HE* he)
           HeSVKEY_set(HE* he, SV* sv)

       These two lower level macros are defined, but must only be
       used when dealing with keys that are not SV*s:

           HeKEY(HE* he)
           HeKLEN(HE* he)

       Note that both hv_store and hv_store_ent do not increment
       the reference count of the stored val, which is the
       caller's responsibility.  If these functions return a NULL
       value, the caller will usually have to decrement the
       reference count of val to avoid a memory leak.

       RReeffeerreenncceess

       References are a special type of scalar that point to
       other data types (including references).

       To create a reference, use either of the following
       functions:

           SV* newRV_inc((SV*) thing);
           SV* newRV_noinc((SV*) thing);

       The thing argument can be any of an SV*, AV*, or HV*.  The
       functions are identical except that newRV_inc increments
       the reference count of the thing, while newRV_noinc does
       not.  For historical reasons, newRV is a synonym for
       newRV_inc.

       Once you have a reference, you can use the following macro
       to dereference the reference:

           SvRV(SV*)

       then call the appropriate routines, casting the returned
       SV* to either an AV* or HV*, if required.

       To determine if an SV is a reference, you can use the
       following macro:

           SvROK(SV*)

       To discover what type of value the reference refers to,
       use the following macro and then check the return value.

           SvTYPE(SvRV(SV*))

       The most useful types that will be returned are:

           SVt_IV    Scalar
           SVt_NV    Scalar
           SVt_PV    Scalar
           SVt_RV    Scalar
           SVt_PVAV  Array
           SVt_PVHV  Hash
           SVt_PVCV  Code
           SVt_PVGV  Glob (possible a file handle)
           SVt_PVMG  Blessed or Magical Scalar

           See the sv.h header file for more details.

       BBlleesssseedd RReeffeerreenncceess aanndd CCllaassss OObbjjeeccttss

       References are also used to support object-oriented
       programming.  In the OO lexicon, an object is simply a
       reference that has been blessed into a package (or class).
       Once blessed, the programmer may now use the reference to
       access the various methods in the class.

       A reference can be blessed into a package with the
       following function:

           SV* sv_bless(SV* sv, HV* stash);

       The sv argument must be a reference.  The stash argument
       specifies which class the reference will belong to.  See
       the section on Stashes and Globs for information on
       converting class names into stashes.

       /* Still under construction */

       Upgrades rv to reference if not already one.  Creates new
       SV for rv to point to.  If classname is non-null, the SV
       is blessed into the specified class.  SV is returned.

               SV* newSVrv(SV* rv, char* classname);

       Copies integer or double into an SV whose reference is rv.
       SV is blessed if classname is non-null.

               SV* sv_setref_iv(SV* rv, char* classname, IV iv);
               SV* sv_setref_nv(SV* rv, char* classname, NV iv);

       Copies the pointer value (the address, not the string!)
       into an SV whose reference is rv.  SV is blessed if
       classname is non-null.

               SV* sv_setref_pv(SV* rv, char* classname, PV iv);

       Copies string into an SV whose reference is rv.  Set
       length to 0 to let Perl calculate the string length.  SV
       is blessed if classname is non-null.

               SV* sv_setref_pvn(SV* rv, char* classname, PV iv, STRLEN length);

       Tests whether the SV is blessed into the specified class.
       It does not check inheritance relationships.

               int  sv_isa(SV* sv, char* name);

       Tests whether the SV is a reference to a blessed object.

               int  sv_isobject(SV* sv);

       Tests whether the SV is derived from the specified class.
       SV can be either a reference to a blessed object or a
       string containing a class name. This is the function
       implementing the UNIVERSAL::isa functionality.

               bool sv_derived_from(SV* sv, char* name);

       To check if you've got an object derived from a specific
       class you have to write:

               if (sv_isobject(sv) && sv_derived_from(sv, class)) { ... }

       CCrreeaattiinngg NNeeww VVaarriiaabblleess

       To create a new Perl variable with an undef value which
       can be accessed from your Perl script, use the following
       routines, depending on the variable type.

           SV*  perl_get_sv("package::varname", TRUE);
           AV*  perl_get_av("package::varname", TRUE);
           HV*  perl_get_hv("package::varname", TRUE);

       Notice the use of TRUE as the second parameter.  The new
       variable can now be set, using the routines appropriate to
       the data type.

       There are additional macros whose values may be bitwise
       OR'ed with the TRUE argument to enable certain extra
       features.  Those bits are:

           GV_ADDMULTI Marks the variable as multiply defined, thus preventing the
                       "Name <varname> used only once: possible typo" warning.
           GV_ADDWARN  Issues the warning "Had to create <varname> unexpectedly" if
                       the variable did not exist before the function was called.

       If you do not specify a package name, the variable is
       created in the current package.

       RReeffeerreennccee CCoouunnttss aanndd MMoorrttaalliittyy

       Perl uses an reference count-driven garbage collection
       mechanism. SVs, AVs, or HVs (xV for short in the
       following) start their life with a reference count of 1.
       If the reference count of an xV ever drops to 0, then it
       will be destroyed and its memory made available for reuse.

       This normally doesn't happen at the Perl level unless a
       variable is undef'ed or the last variable holding a
       reference to it is changed or overwritten.  At the
       internal level, however, reference counts can be
       manipulated with the following macros:

           int SvREFCNT(SV* sv);
           SV* SvREFCNT_inc(SV* sv);
           void SvREFCNT_dec(SV* sv);

       However, there is one other function which manipulates the
       reference count of its argument.  The newRV_inc function,
       you will recall, creates a reference to the specified
       argument.  As a side effect, it increments the argument's
       reference count.  If this is not what you want, use
       newRV_noinc instead.

       For example, imagine you want to return a reference from
       an XSUB function.  Inside the XSUB routine, you create an
       SV which initially has a reference count of one.  Then you
       call newRV_inc, passing it the just-created SV.  This
       returns the reference as a new SV, but the reference count
       of the SV you passed to newRV_inc has been incremented to
       two.  Now you return the reference from the XSUB routine
       and forget about the SV.  But Perl hasn't!  Whenever the
       returned reference is destroyed, the reference count of
       the original SV is decreased to one and nothing happens.
       The SV will hang around without any way to access it until
       Perl itself terminates.  This is a memory leak.

       The correct procedure, then, is to use newRV_noinc instead
       of newRV_inc.  Then, if and when the last reference is
       destroyed, the reference count of the SV will go to zero
       and it will be destroyed, stopping any memory leak.

       There are some convenience functions available that can
       help with the destruction of xVs.  These functions
       introduce the concept of "mortality".  An xV that is
       mortal has had its reference count marked to be
       decremented, but not actually decremented, until "a short
       time later".  Generally the term "short time later" means
       a single Perl statement, such as a call to an XSUB
       function.  The actual determinant for when mortal xVs have
       their reference count decremented depends on two macros,
       SAVETMPS and FREETMPS.  See the perlcall manpage and the
       perlxs manpage for more details on these macros.

       "Mortalization" then is at its simplest a deferred
       SvREFCNT_dec.  However, if you mortalize a variable twice,
       the reference count will later be decremented twice.

       You should be careful about creating mortal variables.
       Strange things can happen if you make the same value
       mortal within multiple contexts, or if you make a variable
       mortal multiple times.

       To create a mortal variable, use the functions:

           SV*  sv_newmortal()
           SV*  sv_2mortal(SV*)
           SV*  sv_mortalcopy(SV*)

       The first call creates a mortal SV, the second converts an
       existing SV to a mortal SV (and thus defers a call to
       SvREFCNT_dec), and the third creates a mortal copy of an
       existing SV.

       The mortal routines are not just for SVs -- AVs and HVs
       can be made mortal by passing their address (type-casted
       to SV*) to the sv_2mortal or sv_mortalcopy routines.

       SSttaasshheess aanndd GGlloobbss

       A "stash" is a hash that contains all of the different
       objects that are contained within a package.  Each key of
       the stash is a symbol name (shared by all the different
       types of objects that have the same name), and each value
       in the hash table is a GV (Glob Value).  This GV in turn
       contains references to the various objects of that name,
       including (but not limited to) the following:

           Scalar Value
           Array Value
           Hash Value
           I/O Handle
           Format
           Subroutine

       There is a single stash called "PL_defstash" that holds
       the items that exist in the "main" package.  To get at the
       items in other packages, append the string "::" to the
       package name.  The items in the "Foo" package are in the
       stash "Foo::" in PL_defstash.  The items in the "Bar::Baz"
       package are in the stash "Baz::" in "Bar::"'s stash.

       To get the stash pointer for a particular package, use the
       function:

           HV*  gv_stashpv(char* name, I32 create)
           HV*  gv_stashsv(SV*, I32 create)

       The first function takes a literal string, the second uses
       the string stored in the SV.  Remember that a stash is
       just a hash table, so you get back an HV*.  The create
       flag will create a new package if it is set.

       The name that gv_stash*v wants is the name of the package
       whose symbol table you want.  The default package is
       called main.  If you have multiply nested packages, pass
       their names to gv_stash*v, separated by :: as in the Perl
       language itself.

       Alternately, if you have an SV that is a blessed
       reference, you can find out the stash pointer by using:

           HV*  SvSTASH(SvRV(SV*));

       then use the following to get the package name itself:

           char*  HvNAME(HV* stash);

       If you need to bless or re-bless an object you can use the
       following function:

           SV*  sv_bless(SV*, HV* stash)

       where the first argument, an SV*, must be a reference, and
       the second argument is a stash.  The returned SV* can now
       be used in the same way as any other SV.

       For more information on references and blessings, consult
       the perlref manpage.

       DDoouubbllee--TTyyppeedd SSVVss

       Scalar variables normally contain only one type of value,
       an integer, double, pointer, or reference.  Perl will
       automatically convert the actual scalar data from the
       stored type into the requested type.

       Some scalar variables contain more than one type of scalar
       data.  For example, the variable $! contains either the
       numeric value of errno or its string equivalent from
       either strerror or sys_errlist[].

       To force multiple data values into an SV, you must do two
       things: use the sv_set*v routines to add the additional
       scalar type, then set a flag so that Perl will believe it
       contains more than one type of data.  The four macros to
       set the flags are:

               SvIOK_on
               SvNOK_on
               SvPOK_on
               SvROK_on

       The particular macro you must use depends on which
       sv_set*v routine you called first.  This is because every
       sv_set*v routine turns on only the bit for the particular
       type of data being set, and turns off all the rest.

       For example, to create a new Perl variable called
       "dberror" that contains both the numeric and descriptive
       string error values, you could use the following code:

           extern int  dberror;
           extern char *dberror_list;

           SV* sv = perl_get_sv("dberror", TRUE);
           sv_setiv(sv, (IV) dberror);
           sv_setpv(sv, dberror_list[dberror]);
           SvIOK_on(sv);

       If the order of sv_setiv and sv_setpv had been reversed,
       then the macro SvPOK_on would need to be called instead of
       SvIOK_on.

       MMaaggiicc VVaarriiaabblleess

       [This section still under construction.  Ignore everything
       here.  Post no bills.  Everything not permitted is
       forbidden.]

       Any SV may be magical, that is, it has special features
       that a normal SV does not have.  These features are stored
       in the SV structure in a linked list of struct magic's,
       typedef'ed to MAGIC.

           struct magic {
               MAGIC*      mg_moremagic;
               MGVTBL*     mg_virtual;
               U16         mg_private;
               char        mg_type;
               U8          mg_flags;
               SV*         mg_obj;
               char*       mg_ptr;
               I32         mg_len;
           };

       Note this is current as of patchlevel 0, and could change
       at any time.

       AAssssiiggnniinngg MMaaggiicc

       Perl adds magic to an SV using the sv_magic function:

           void sv_magic(SV* sv, SV* obj, int how, char* name, I32 namlen);

       The sv argument is a pointer to the SV that is to acquire
       a new magical feature.

       If sv is not already magical, Perl uses the SvUPGRADE
       macro to set the SVt_PVMG flag for the sv.  Perl then
       continues by adding it to the beginning of the linked list
       of magical features.  Any prior entry of the same type of
       magic is deleted.  Note that this can be overridden, and
       multiple instances of the same type of magic can be
       associated with an SV.

       The name and namlen arguments are used to associate a
       string with the magic, typically the name of a variable.
       namlen is stored in the mg_len field and if name is non-
       null and namlen >= 0 a malloc'd copy of the name is stored
       in mg_ptr field.

       The sv_magic function uses how to determine which, if any,
       predefined "Magic Virtual Table" should be assigned to the
       mg_virtual field.  See the "Magic Virtual Table" section
       below.  The how argument is also stored in the mg_type
       field.

       The obj argument is stored in the mg_obj field of the
       MAGIC structure.  If it is not the same as the sv
       argument, the reference count of the obj object is
       incremented.  If it is the same, or if the how argument is
       "#", or if it is a NULL pointer, then obj is merely
       stored, without the reference count being incremented.

       There is also a function to add magic to an HV:

           void hv_magic(HV *hv, GV *gv, int how);

       This simply calls sv_magic and coerces the gv argument
       into an SV.

       To remove the magic from an SV, call the function
       sv_unmagic:

           void sv_unmagic(SV *sv, int type);

       The type argument should be equal to the how value when
       the SV was initially made magical.

       MMaaggiicc VViirrttuuaall TTaabblleess

       The mg_virtual field in the MAGIC structure is a pointer
       to a MGVTBL, which is a structure of function pointers and
       stands for "Magic Virtual Table" to handle the various
       operations that might be applied to that variable.

       The MGVTBL has five pointers to the following routine
       types:

           int  (*svt_get)(SV* sv, MAGIC* mg);
           int  (*svt_set)(SV* sv, MAGIC* mg);
           U32  (*svt_len)(SV* sv, MAGIC* mg);
           int  (*svt_clear)(SV* sv, MAGIC* mg);
           int  (*svt_free)(SV* sv, MAGIC* mg);

       This MGVTBL structure is set at compile-time in perl.h and
       there are currently 19 types (or 21 with overloading
       turned on).  These different structures contain pointers
       to various routines that perform additional actions
       depending on which function is being called.

           Function pointer    Action taken
           ----------------    ------------
           svt_get             Do something after the value of the SV is retrieved.
           svt_set             Do something after the SV is assigned a value.
           svt_len             Report on the SV's length.
           svt_clear           Clear something the SV represents.
           svt_free            Free any extra storage associated with the SV.

       For instance, the MGVTBL structure called vtbl_sv (which
       corresponds to an mg_type of '\0') contains:

           { magic_get, magic_set, magic_len, 0, 0 }

       Thus, when an SV is determined to be magical and of type
       '\0', if a get operation is being performed, the routine
       magic_get is called.  All the various routines for the
       various magical types begin with magic_.

       The current kinds of Magic Virtual Tables are:

           mg_type  MGVTBL              Type of magic
           -------  ------              ----------------------------
           \0       vtbl_sv             Special scalar variable
           A        vtbl_amagic         %OVERLOAD hash
           a        vtbl_amagicelem     %OVERLOAD hash element
           c        (none)              Holds overload table (AMT) on stash
           B        vtbl_bm             Boyer-Moore (fast string search)
           E        vtbl_env            %ENV hash
           e        vtbl_envelem        %ENV hash element
           f        vtbl_fm             Formline ('compiled' format)
           g        vtbl_mglob          m//g target / study()ed string
           I        vtbl_isa            @ISA array
           i        vtbl_isaelem        @ISA array element
           k        vtbl_nkeys          scalar(keys()) lvalue
           L        (none)              Debugger %_<filename
           l        vtbl_dbline         Debugger %_<filename element
           o        vtbl_collxfrm       Locale transformation
           P        vtbl_pack           Tied array or hash
           p        vtbl_packelem       Tied array or hash element
           q        vtbl_packelem       Tied scalar or handle
           S        vtbl_sig            %SIG hash
           s        vtbl_sigelem        %SIG hash element
           t        vtbl_taint          Taintedness
           U        vtbl_uvar           Available for use by extensions
           v        vtbl_vec            vec() lvalue
           x        vtbl_substr         substr() lvalue
           y        vtbl_defelem        Shadow "foreach" iterator variable /
                                         smart parameter vivification
           *        vtbl_glob           GV (typeglob)
           #        vtbl_arylen         Array length ($#ary)
           .        vtbl_pos            pos() lvalue
           ~        (none)              Available for use by extensions

       When an uppercase and lowercase letter both exist in the
       table, then the uppercase letter is used to represent some
       kind of composite type (a list or a hash), and the
       lowercase letter is used to represent an element of that
       composite type.

       The '~' and 'U' magic types are defined specifically for
       use by extensions and will not be used by perl itself.
       Extensions can use '~' magic to 'attach' private
       information to variables (typically objects).  This is
       especially useful because there is no way for normal perl
       code to corrupt this private information (unlike using
       extra elements of a hash object).

       Similarly, 'U' magic can be used much like tie() to call a
       C function any time a scalar's value is used or changed.
       The MAGIC's mg_ptr field points to a ufuncs structure:

           struct ufuncs {
               I32 (*uf_val)(IV, SV*);
               I32 (*uf_set)(IV, SV*);
               IV uf_index;
           };

       When the SV is read from or written to, the uf_val or
       uf_set function will be called with uf_index as the first
       arg and a pointer to the SV as the second.  A simple
       example of how to add 'U' magic is shown below.  Note that
       the ufuncs structure is copied by sv_magic, so you can
       safely allocate it on the stack.

           void
           Umagic(sv)
               SV *sv;
           PREINIT:
               struct ufuncs uf;
           CODE:
               uf.uf_val   = &my_get_fn;
               uf.uf_set   = &my_set_fn;
               uf.uf_index = 0;
               sv_magic(sv, 0, 'U', (char*)&uf, sizeof(uf));

       Note that because multiple extensions may be using '~' or
       'U' magic, it is important for extensions to take extra
       care to avoid conflict.  Typically only using the magic on
       objects blessed into the same class as the extension is
       sufficient.  For '~' magic, it may also be appropriate to
       add an I32 'signature' at the top of the private data area
       and check that.

       Also note that the sv_set*() and sv_cat*() functions
       described earlier do nnoott invoke 'set' magic on their
       targets.  This must be done by the user either by calling
       the SvSETMAGIC() macro after calling these functions, or
       by using one of the sv_set*_mg() or sv_cat*_mg()
       functions.  Similarly, generic C code must call the
       SvGETMAGIC() macro to invoke any 'get' magic if they use
       an SV obtained from external sources in functions that
       don't handle magic.  the section on API LISTING later in
       this document identifies such functions.  For example,
       calls to the sv_cat*() functions typically need to be
       followed by SvSETMAGIC(), but they don't need a prior
       SvGETMAGIC() since their implementation handles 'get'
       magic.

       FFiinnddiinngg MMaaggiicc

           MAGIC* mg_find(SV*, int type); /* Finds the magic pointer of that type */

       This routine returns a pointer to the MAGIC structure
       stored in the SV.  If the SV does not have that magical
       feature, NULL is returned.  Also, if the SV is not of type
       SVt_PVMG, Perl may core dump.

           int mg_copy(SV* sv, SV* nsv, char* key, STRLEN klen);

       This routine checks to see what types of magic sv has.  If
       the mg_type field is an uppercase letter, then the mg_obj
       is copied to nsv, but the mg_type field is changed to be
       the lowercase letter.

       UUnnddeerrssttaannddiinngg tthhee MMaaggiicc ooff TTiieedd HHaasshheess aanndd AArrrraayyss

       Tied hashes and arrays are magical beasts of the 'P' magic
       type.

       WARNING: As of the 5.004 release, proper usage of the
       array and hash access functions requires understanding a
       few caveats.  Some of these caveats are actually
       considered bugs in the API, to be fixed in later releases,
       and are bracketed with [MAYCHANGE] below. If you find
       yourself actually applying such information in this
       section, be aware that the behavior may change in the
       future, umm, without warning.

       The perl tie function associates a variable with an object
       that implements the various GET, SET etc methods.  To
       perform the equivalent of the perl tie function from an
       XSUB, you must mimic this behaviour.  The code below
       carries out the necessary steps - firstly it creates a new
       hash, and then creates a second hash which it blesses into
       the class which will implement the tie methods. Lastly it
       ties the two hashes together, and returns a reference to
       the new tied hash.  Note that the code below does NOT call
       the TIEHASH method in the MyTie class - see the section on
       Calling Perl Routines from within C Programs for details
       on how to do this.

           SV*
           mytie()
           PREINIT:
               HV *hash;
               HV *stash;
               SV *tie;
           CODE:
               hash = newHV();
               tie = newRV_noinc((SV*)newHV());
               stash = gv_stashpv("MyTie", TRUE);
               sv_bless(tie, stash);
               hv_magic(hash, tie, 'P');
               RETVAL = newRV_noinc(hash);
           OUTPUT:
               RETVAL

       The av_store function, when given a tied array argument,
       merely copies the magic of the array onto the value to be
       "stored", using mg_copy.  It may also return NULL,
       indicating that the value did not actually need to be
       stored in the array.  [MAYCHANGE] After a call to av_store
       on a tied array, the caller will usually need to call
       mg_set(val) to actually invoke the perl level "STORE"
       method on the TIEARRAY object.  If av_store did return
       NULL, a call to SvREFCNT_dec(val) will also be usually
       necessary to avoid a memory leak. [/MAYCHANGE]

       The previous paragraph is applicable verbatim to tied hash
       access using the hv_store and hv_store_ent functions as
       well.

       av_fetch and the corresponding hash functions hv_fetch and
       hv_fetch_ent actually return an undefined mortal value
       whose magic has been initialized using mg_copy.  Note the
       value so returned does not need to be deallocated, as it
       is already mortal.  [MAYCHANGE] But you will need to call
       mg_get() on the returned value in order to actually invoke
       the perl level "FETCH" method on the underlying TIE
       object.  Similarly, you may also call mg_set() on the
       return value after possibly assigning a suitable value to
       it using sv_setsv,  which will invoke the "STORE" method
       on the TIE object. [/MAYCHANGE]

       [MAYCHANGE] In other words, the array or hash fetch/store
       functions don't really fetch and store actual values in
       the case of tied arrays and hashes.  They merely call
       mg_copy to attach magic to the values that were meant to
       be "stored" or "fetched".  Later calls to mg_get and
       mg_set actually do the job of invoking the TIE methods on
       the underlying objects.  Thus the magic mechanism
       currently implements a kind of lazy access to arrays and
       hashes.

       Currently (as of perl version 5.004), use of the hash and
       array access functions requires the user to be aware of
       whether they are operating on "normal" hashes and arrays,
       or on their tied variants.  The API may be changed to
       provide more transparent access to both tied and normal
       data types in future versions.  [/MAYCHANGE]

       You would do well to understand that the TIEARRAY and
       TIEHASH interfaces are mere sugar to invoke some perl
       method calls while using the uniform hash and array
       syntax.  The use of this sugar imposes some overhead
       (typically about two to four extra opcodes per FETCH/STORE
       operation, in addition to the creation of all the mortal
       variables required to invoke the methods).  This overhead
       will be comparatively small if the TIE methods are
       themselves substantial, but if they are only a few
       statements long, the overhead will not be insignificant.

       LLooccaalliizziinngg cchhaannggeess

       Perl has a very handy construction

         {
           local $var = 2;
           ...
         }

       This construction is approximately equivalent to

         {
           my $oldvar = $var;
           $var = 2;
           ...
           $var = $oldvar;
         }

       The biggest difference is that the first construction
       would reinstate the initial value of $var, irrespective of
       how control exits the block: goto, return, die/eval etc.
       It is a little bit more efficient as well.

       There is a way to achieve a similar task from C via Perl
       API: create a pseudo-block, and arrange for some changes
       to be automatically undone at the end of it, either
       explicit, or via a non-local exit (via die()). A
       block-like construct is created by a pair of ENTER/LEAVE
       macros (see the section on Returning a Scalar in the
       perlcall manpage).  Such a construct may be created
       specially for some important localized task, or an
       existing one (like boundaries of enclosing Perl
       subroutine/block, or an existing pair for freeing TMPs)
       may be used. (In the second case the overhead of
       additional localization must be almost negligible.) Note
       that any XSUB is automatically enclosed in an ENTER/LEAVE
       pair.

       Inside such a pseudo-block the following service is
       available:

       SAVEINT(int i)

       SAVEIV(IV i)

       SAVEI32(I32 i)

       SAVELONG(long i)
            These macros arrange things to restore the value of
            integer variable i at the end of enclosing pseudo-
            block.

       SAVESPTR(s)

       SAVEPPTR(p)
            These macros arrange things to restore the value of
            pointers s and p. s must be a pointer of a type which
            survives conversion to SV* and back, p should be able
            to survive conversion to char* and back.

       SAVEFREESV(SV *sv)
            The refcount of sv would be decremented at the end of
            pseudo-block. This is similar to sv_2mortal, which
            should (?) be used instead.

       SAVEFREEOP(OP *op)
            The OP * is op_free()ed at the end of pseudo-block.

       SAVEFREEPV(p)
            The chunk of memory which is pointed to by p is
            Safefree()ed at the end of pseudo-block.

       SAVECLEARSV(SV *sv)
            Clears a slot in the current scratchpad which
            corresponds to sv at the end of pseudo-block.

       SAVEDELETE(HV *hv, char *key, I32 length)
            The key key of hv is deleted at the end of pseudo-
            block. The string pointed to by key is Safefree()ed.
            If one has a key in short-lived storage, the
            corresponding string may be reallocated like this:

              SAVEDELETE(PL_defstash, savepv(tmpbuf), strlen(tmpbuf));

       SAVEDESTRUCTOR(f,p)
            At the end of pseudo-block the function f is called
            with the only argument (of type void*) p.

       SAVESTACK_POS()
            The current offset on the Perl internal stack (cf.
            SP) is restored at the end of pseudo-block.

       The following API list contains functions, thus one needs
       to provide pointers to the modifiable data explicitly
       (either C pointers, or Perlish GV *s).  Where the above
       macros take int, a similar function takes int *.

       SV* save_scalar(GV *gv)
            Equivalent to Perl code local $gv.

       AV* save_ary(GV *gv)

       HV* save_hash(GV *gv)
            Similar to save_scalar, but localize @gv and %gv.

       void save_item(SV *item)
            Duplicates the current value of SV, on the exit from
            the current ENTER/LEAVE pseudo-block will restore the
            value of SV using the stored value.

       void save_list(SV **sarg, I32 maxsarg)
            A variant of save_item which takes multiple arguments
            via an array sarg of SV* of length maxsarg.

       SV* save_svref(SV **sptr)
            Similar to save_scalar, but will reinstate a SV *.

       void save_aptr(AV **aptr)

       void save_hptr(HV **hptr)
            Similar to save_svref, but localize AV * and HV *.

       The Alias module implements localization of the basic
       types within the caller's scope.  People who are
       interested in how to localize things in the containing
       scope should take a look there too.

SSuubbrroouuttiinneess
       XXSSUUBBss aanndd tthhee AArrgguummeenntt SSttaacckk

       The XSUB mechanism is a simple way for Perl programs to
       access C subroutines.  An XSUB routine will have a stack
       that contains the arguments from the Perl program, and a
       way to map from the Perl data structures to a C
       equivalent.

       The stack arguments are accessible through the ST(n)
       macro, which returns the n'th stack argument.  Argument 0
       is the first argument passed in the Perl subroutine call.
       These arguments are SV*, and can be used anywhere an SV*
       is used.

       Most of the time, output from the C routine can be handled
       through use of the RETVAL and OUTPUT directives.  However,
       there are some cases where the argument stack is not
       already long enough to handle all the return values.  An
       example is the POSIX tzname() call, which takes no
       arguments, but returns two, the local time zone's standard
       and summer time abbreviations.

       To handle this situation, the PPCODE directive is used and
       the stack is extended using the macro:

           EXTEND(SP, num);

       where SP is the macro that represents the local copy of
       the stack pointer, and num is the number of elements the
       stack should be extended by.

       Now that there is room on the stack, values can be pushed
       on it using the macros to push IVs, doubles, strings, and
       SV pointers respectively:

           PUSHi(IV)
           PUSHn(double)
           PUSHp(char*, I32)
           PUSHs(SV*)

       And now the Perl program calling tzname, the two values
       will be assigned as in:

           ($standard_abbrev, $summer_abbrev) = POSIX::tzname;

       An alternate (and possibly simpler) method to pushing
       values on the stack is to use the macros:

           XPUSHi(IV)
           XPUSHn(double)
           XPUSHp(char*, I32)
           XPUSHs(SV*)

       These macros automatically adjust the stack for you, if
       needed.  Thus, you do not need to call EXTEND to extend
       the stack.

       For more information, consult the perlxs manpage and the
       perlxstut manpage.

       CCaalllliinngg PPeerrll RRoouuttiinneess ffrroomm wwiitthhiinn CC PPrrooggrraammss

       There are four routines that can be used to call a Perl
       subroutine from within a C program.  These four are:

           I32  perl_call_sv(SV*, I32);
           I32  perl_call_pv(char*, I32);
           I32  perl_call_method(char*, I32);
           I32  perl_call_argv(char*, I32, register char**);

       The routine most often used is perl_call_sv.  The SV*
       argument contains either the name of the Perl subroutine
       to be called, or a reference to the subroutine.  The
       second argument consists of flags that control the context
       in which the subroutine is called, whether or not the
       subroutine is being passed arguments, how errors should be
       trapped, and how to treat return values.

       All four routines return the number of arguments that the
       subroutine returned on the Perl stack.

       When using any of these routines (except perl_call_argv),
       the programmer must manipulate the Perl stack.  These
       include the following macros and functions:

           dSP
           SP
           PUSHMARK()
           PUTBACK
           SPAGAIN
           ENTER
           SAVETMPS
           FREETMPS
           LEAVE
           XPUSH*()
           POP*()

       For a detailed description of calling conventions from C
       to Perl, consult the perlcall manpage.

       MMeemmoorryy AAllllooccaattiioonn

       All memory meant to be used with the Perl API functions
       should be manipulated using the macros described in this
       section.  The macros provide the necessary transparency
       between differences in the actual malloc implementation
       that is used within perl.

       It is suggested that you enable the version of malloc that
       is distributed with Perl.  It keeps pools of various sizes
       of unallocated memory in order to satisfy allocation
       requests more quickly.  However, on some platforms, it may
       cause spurious malloc or free errors.

           New(x, pointer, number, type);
           Newc(x, pointer, number, type, cast);
           Newz(x, pointer, number, type);

       These three macros are used to initially allocate memory.

       The first argument x was a "magic cookie" that was used to
       keep track of who called the macro, to help when debugging
       memory problems.  However, the current code makes no use
       of this feature (most Perl developers now use run-time
       memory checkers), so this argument can be any number.

       The second argument pointer should be the name of a
       variable that will point to the newly allocated memory.

       The third and fourth arguments number and type specify how
       many of the specified type of data structure should be
       allocated.  The argument type is passed to sizeof.  The
       final argument to Newc, cast, should be used if the
       pointer argument is different from the type argument.

       Unlike the New and Newc macros, the Newz macro calls
       memzero to zero out all the newly allocated memory.

           Renew(pointer, number, type);
           Renewc(pointer, number, type, cast);
           Safefree(pointer)

       These three macros are used to change a memory buffer size
       or to free a piece of memory no longer needed.  The
       arguments to Renew and Renewc match those of New and Newc
       with the exception of not needing the "magic cookie"
       argument.

           Move(source, dest, number, type);
           Copy(source, dest, number, type);
           Zero(dest, number, type);

       These three macros are used to move, copy, or zero out
       previously allocated memory.  The source and dest
       arguments point to the source and destination starting
       points.  Perl will move, copy, or zero out number
       instances of the size of the type data structure (using
       the sizeof function).

       PPeerrllIIOO

       The most recent development releases of Perl has been
       experimenting with removing Perl's dependency on the
       "normal" standard I/O suite and allowing other stdio
       implementations to be used.  This involves creating a new
       abstraction layer that then calls whichever implementation
       of stdio Perl was compiled with.  All XSUBs should now use
       the functions in the PerlIO abstraction layer and not make
       any assumptions about what kind of stdio is being used.

       For a complete description of the PerlIO abstraction,
       consult the perlapio manpage.

       PPuuttttiinngg aa CC vvaalluuee oonn PPeerrll ssttaacckk

       A lot of opcodes (this is an elementary operation in the
       internal perl stack machine) put an SV* on the stack.
       However, as an optimization the corresponding SV is
       (usually) not recreated each time. The opcodes reuse
       specially assigned SVs (targets) which are (as a
       corollary) not constantly freed/created.

       Each of the targets is created only once (but see the
       section on Scratchpads and recursion below), and when an
       opcode needs to put an integer, a double, or a string on
       stack, it just sets the corresponding parts of its target
       and puts the target on stack.

       The macro to put this target on stack is PUSHTARG, and it
       is directly used in some opcodes, as well as indirectly in
       zillions of others, which use it via (X)PUSH[pni].

       SSccrraattcchhppaaddss

       The question remains on when the SVs which are targets for
       opcodes are created. The answer is that they are created
       when the current unit -- a subroutine or a file (for
       opcodes for statements outside of subroutines) -- is
       compiled. During this time a special anonymous Perl array
       is created, which is called a scratchpad for the current
       unit.

       A scratchpad keeps SVs which are lexicals for the current
       unit and are targets for opcodes. One can deduce that an
       SV lives on a scratchpad by looking on its flags: lexicals
       have SVs_PADMY set, and targets have SVs_PADTMP set.

       The correspondence between OPs and targets is not 1-to-1.
       Different OPs in the compile tree of the unit can use the
       same target, if this would not conflict with the expected
       life of the temporary.

       SSccrraattcchhppaaddss aanndd rreeccuurrssiioonn

       In fact it is not 100% true that a compiled unit contains
       a pointer to the scratchpad AV. In fact it contains a
       pointer to an AV of (initially) one element, and this
       element is the scratchpad AV. Why do we need an extra
       level of indirection?

       The answer is rreeccuurrssiioonn, and maybe (sometime soon)
       tthhrreeaaddss. Both these can create several execution pointers
       going into the same subroutine. For the subroutine-child
       not write over the temporaries for the subroutine-parent
       (lifespan of which covers the call to the child), the
       parent and the child should have different scratchpads.
       (And the lexicals should be separate anyway!)

       So each subroutine is born with an array of scratchpads
       (of length 1).  On each entry to the subroutine it is
       checked that the current depth of the recursion is not
       more than the length of this array, and if it is, new
       scratchpad is created and pushed into the array.

       The targets on this scratchpad are undefs, but they are
       already marked with correct flags.

CCoommppiilleedd ccooddee
       CCooddee ttrreeee

       Here we describe the internal form your code is converted
       to by Perl. Start with a simple example:

         $a = $b + $c;

       This is converted to a tree similar to this one:

                    assign-to
                  /           \
                 +             $a
               /   \
             $b     $c

       (but slightly more complicated).  This tree reflects the
       way Perl parsed your code, but has nothing to do with the
       execution order.  There is an additional "thread" going
       through the nodes of the tree which shows the order of
       execution of the nodes.  In our simplified example above
       it looks like:

            $b ---> $c ---> + ---> $a ---> assign-to

       But with the actual compile tree for $a = $b + $c it is
       different: some nodes optimized away.  As a corollary,
       though the actual tree contains more nodes than our
       simplified example, the execution order is the same as in
       our example.

       EExxaammiinniinngg tthhee ttrreeee

       If you have your perl compiled for debugging (usually done
       with -D optimize=-g on Configure command line), you may
       examine the compiled tree by specifying -Dx on the Perl
       command line.  The output takes several lines per node,
       and for $b+$c it looks like this:

           5           TYPE = add  ===> 6
                       TARG = 1
                       FLAGS = (SCALAR,KIDS)
                       {
                           TYPE = null  ===> (4)
                             (was rv2sv)
                           FLAGS = (SCALAR,KIDS)
                           {
           3                   TYPE = gvsv  ===> 4
                               FLAGS = (SCALAR)
                               GV = main::b
                           }
                       }
                       {
                           TYPE = null  ===> (5)
                             (was rv2sv)
                           FLAGS = (SCALAR,KIDS)
                           {
           4                   TYPE = gvsv  ===> 5
                               FLAGS = (SCALAR)
                               GV = main::c
                           }
                       }

       This tree has 5 nodes (one per TYPE specifier), only 3 of
       them are not optimized away (one per number in the left
       column).  The immediate children of the given node
       correspond to {} pairs on the same level of indentation,
       thus this listing corresponds to the tree:

                          add
                        /     \
                      null    null
                       |       |
                      gvsv    gvsv

       The execution order is indicated by ===> marks, thus it is
       3 4 5 6 (node 6 is not included into above listing), i.e.,
       gvsv gvsv add whatever.

       CCoommppiillee ppaassss 11:: cchheecckk rroouuttiinneess

       The tree is created by the pseudo-compiler while yacc code
       feeds it the constructions it recognizes. Since yacc works
       bottom-up, so does the first pass of perl compilation.

       What makes this pass interesting for perl developers is
       that some optimization may be performed on this pass.
       This is optimization by so-called check routines.  The
       correspondence between node names and corresponding check
       routines is described in opcode.pl (do not forget to run
       make regen_headers if you modify this file).

       A check routine is called when the node is fully
       constructed except for the execution-order thread.  Since
       at this time there are no back-links to the currently
       constructed node, one can do most any operation to the
       top-level node, including freeing it and/or creating new
       nodes above/below it.

       The check routine returns the node which should be
       inserted into the tree (if the top-level node was not
       modified, check routine returns its argument).

       By convention, check routines have names ck_*. They are
       usually called from new*OP subroutines (or convert) (which
       in turn are called from perly.y).

       CCoommppiillee ppaassss 11aa:: ccoonnssttaanntt ffoollddiinngg

       Immediately after the check routine is called the returned
       node is checked for being compile-time executable.  If it
       is (the value is judged to be constant) it is immediately
       executed, and a constant node with the "return value" of
       the corresponding subtree is substituted instead.  The
       subtree is deleted.

       If constant folding was not performed, the execution-order
       thread is created.

       CCoommppiillee ppaassss 22:: ccoonntteexxtt pprrooppaaggaattiioonn

       When a context for a part of compile tree is known, it is
       propagated down through the tree.  At this time the
       context can have 5 values (instead of 2 for runtime
       context): void, boolean, scalar, list, and lvalue.  In
       contrast with the pass 1 this pass is processed from top
       to bottom: a node's context determines the context for its
       children.

       Additional context-dependent optimizations are performed
       at this time.  Since at this moment the compile tree
       contains back-references (via "thread" pointers), nodes
       cannot be free()d now.  To allow optimized-away nodes at
       this stage, such nodes are null()ified instead of
       free()ing (i.e. their type is changed to OP_NULL).

       CCoommppiillee ppaassss 33:: ppeeeepphhoollee ooppttiimmiizzaattiioonn

       After the compile tree for a subroutine (or for an eval or
       a file) is created, an additional pass over the code is
       performed. This pass is neither top-down or bottom-up, but
       in the execution order (with additional complications for
       conditionals).  These optimizations are done in the
       subroutine peep().  Optimizations performed at this stage
       are subject to the same restrictions as in the pass 2.

AAPPII LLIISSTTIINNGG
       This is a listing of functions, macros, flags, and
       variables that may be useful to extension writers or that
       may be found while reading other extensions.

       Note that all Perl API global variables must be referenced
       with the PL_ prefix.  Some macros are provided for
       compatibility with the older, unadorned names, but this
       support will be removed in a future release.

       It is strongly recommended that all Perl API functions
       that don't begin with perl be referenced with an explicit
       Perl_ prefix.

       The sort order of the listing is case insensitive, with
       any occurrences of '_' ignored for the purpose of sorting.

       av_clear
               Clears an array, making it empty.  Does not free
               the memory used by the array itself.

                       void    av_clear (AV* ar)

       av_extend
               Pre-extend an array.  The key is the index to
               which the array should be extended.

                       void    av_extend (AV* ar, I32 key)

       av_fetch
               Returns the SV at the specified index in the
               array.  The key is the index.  If lval is set then
               the fetch will be part of a store.  Check that the
               return value is non-null before dereferencing it
               to a SV*.

               See the section on Understanding the Magic of Tied
               Hashes and Arrays for more information on how to
               use this function on tied arrays.

                       SV**    av_fetch (AV* ar, I32 key, I32 lval)

       AvFILL  Same as av_len().  Deprecated, use av_len()
               instead.

       av_len  Returns the highest index in the array.  Returns
               -1 if the array is empty.

                       I32     av_len (AV* ar)

       av_make Creates a new AV and populates it with a list of
               SVs.  The SVs are copied into the array, so they
               may be freed after the call to av_make.  The new
               AV will have a reference count of 1.

                       AV*     av_make (I32 size, SV** svp)

       av_pop  Pops an SV off the end of the array.  Returns
               &PL_sv_undef if the array is empty.

                       SV*     av_pop (AV* ar)

       av_push Pushes an SV onto the end of the array.  The array
               will grow automatically to accommodate the
               addition.

                       void    av_push (AV* ar, SV* val)

       av_shift
               Shifts an SV off the beginning of the array.

                       SV*     av_shift (AV* ar)

       av_store
               Stores an SV in an array.  The array index is
               specified as key.  The return value will be NULL
               if the operation failed or if the value did not
               need to be actually stored within the array (as in
               the case of tied arrays).  Otherwise it can be
               dereferenced to get the original SV*.  Note that
               the caller is responsible for suitably
               incrementing the reference count of val before the
               call, and decrementing it if the function returned
               NULL.

               See the section on Understanding the Magic of Tied
               Hashes and Arrays for more information on how to
               use this function on tied arrays.

                       SV**    av_store (AV* ar, I32 key, SV* val)

       av_undef
               Undefines the array.  Frees the memory used by the
               array itself.

                       void    av_undef (AV* ar)

       av_unshift
               Unshift the given number of undef values onto the
               beginning of the array.  The array will grow
               automatically to accommodate the addition.  You
               must then use av_store to assign values to these
               new elements.

                       void    av_unshift (AV* ar, I32 num)

       CLASS   Variable which is setup by xsubpp to indicate the
               class name for a C++ XS constructor.  This is
               always a char*.  See THIS and the section on Using
               XS With C++ in the perlxs manpage.

       Copy    The XSUB-writer's interface to the C memcpy
               function.  The s is the source, d is the
               destination, n is the number of items, and t is
               the type.  May fail on overlapping copies.  See
               also Move.

                       void    Copy( s, d, n, t )

       croak   This is the XSUB-writer's interface to Perl's die
               function.  Use this function the same way you use
               the C printf function.  See warn.

       CvSTASH Returns the stash of the CV.

                       HV*     CvSTASH( SV* sv )

       PL_DBsingle
               When Perl is run in debugging mode, with the --dd
               switch, this SV is a boolean which indicates
               whether subs are being single-stepped.  Single-
               stepping is automatically turned on after every
               step.  This is the C variable which corresponds to
               Perl's $DB::single variable.  See PL_DBsub.

       PL_DBsub
               When Perl is run in debugging mode, with the --dd
               switch, this GV contains the SV which holds the
               name of the sub being debugged.  This is the C
               variable which corresponds to Perl's $DB::sub
               variable.  See PL_DBsingle.  The sub name can be
               found by

                       SvPV( GvSV( PL_DBsub ), len )

       PL_DBtrace
               Trace variable used when Perl is run in debugging
               mode, with the --dd switch.  This is the C variable
               which corresponds to Perl's $DB::trace variable.
               See PL_DBsingle.

       dMARK   Declare a stack marker variable, mark, for the
               XSUB.  See MARK and dORIGMARK.

       dORIGMARK
               Saves the original stack mark for the XSUB.  See
               ORIGMARK.

       PL_dowarn
               The C variable which corresponds to Perl's $^W
               warning variable.

       dSP     Declares a local copy of perl's stack pointer for
               the XSUB, available via the SP macro.  See SP.

       dXSARGS Sets up stack and mark pointers for an XSUB,
               calling dSP and dMARK.  This is usually handled
               automatically by xsubpp.  Declares the items
               variable to indicate the number of items on the
               stack.

       dXSI32  Sets up the ix variable for an XSUB which has
               aliases.  This is usually handled automatically by
               xsubpp.

       do_binmode
               Switches filehandle to binmode.  iotype is what
               IoTYPE(io) would contain.

                       do_binmode(fp, iotype, TRUE);

       ENTER   Opening bracket on a callback.  See LEAVE and the
               perlcall manpage.

                       ENTER;

       EXTEND  Used to extend the argument stack for an XSUB's
               return values.

                       EXTEND( sp, int x )

       fbm_compile
               Analyses the string in order to make fast searches
               on it using fbm_instr() -- the Boyer-Moore
               algorithm.

                       void    fbm_compile(SV* sv, U32 flags)

       fbm_instr
               Returns the location of the SV in the string
               delimited by str and strend.  It returns Nullch if
               the string can't be found.  The sv does not have
               to be fbm_compiled, but the search will not be as
               fast then.

                       char*   fbm_instr(char *str, char *strend, SV *sv, U32 flags)

       FREETMPS
               Closing bracket for temporaries on a callback.
               See SAVETMPS and the perlcall manpage.

                       FREETMPS;

       G_ARRAY Used to indicate array context.  See GIMME_V,
               GIMME and the perlcall manpage.

       G_DISCARD
               Indicates that arguments returned from a callback
               should be discarded.  See the perlcall manpage.

       G_EVAL  Used to force a Perl eval wrapper around a
               callback.  See the perlcall manpage.

       GIMME   A backward-compatible version of GIMME_V which can
               only return G_SCALAR or G_ARRAY; in a void
               context, it returns G_SCALAR.

       GIMME_V The XSUB-writer's equivalent to Perl's wantarray.
               Returns G_VOID, G_SCALAR or G_ARRAY for void,
               scalar or array context, respectively.

       G_NOARGS
               Indicates that no arguments are being sent to a
               callback.  See the perlcall manpage.

       G_SCALAR
               Used to indicate scalar context.  See GIMME_V,
               GIMME, and the perlcall manpage.

       gv_fetchmeth
               Returns the glob with the given name and a defined
               subroutine or NULL.  The glob lives in the given
               stash, or in the stashes accessible via @ISA and
               @UNIVERSAL.

               The argument level should be either 0 or -1.  If
               level==0, as a side-effect creates a glob with the
               given name in the given stash which in the case of
               success contains an alias for the subroutine, and
               sets up caching info for this glob.  Similarly for
               all the searched stashes.

               This function grants "SUPER" token as a postfix of
               the stash name.

               The GV returned from gv_fetchmeth may be a method
               cache entry, which is not visible to Perl code.
               So when calling perl_call_sv, you should not use
               the GV directly; instead, you should use the
               method's CV, which can be obtained from the GV
               with the GvCV macro.

                       GV*     gv_fetchmeth (HV* stash, char* name, STRLEN len, I32 level)

       gv_fetchmethod

       gv_fetchmethod_autoload
               Returns the glob which contains the subroutine to
               call to invoke the method on the stash.  In fact
               in the presence of autoloading this may be the
               glob for "AUTOLOAD".  In this case the
               corresponding variable $AUTOLOAD is already setup.

               The third parameter of gv_fetchmethod_autoload
               determines whether AUTOLOAD lookup is performed if
               the given method is not present: non-zero means
               yes, look for AUTOLOAD; zero means no, don't look
               for AUTOLOAD.  Calling gv_fetchmethod is
               equivalent to calling gv_fetchmethod_autoload with
               a non-zero autoload parameter.

               These functions grant "SUPER" token as a prefix of
               the method name.

               Note that if you want to keep the returned glob
               for a long time, you need to check for it being
               "AUTOLOAD", since at the later time the call may
               load a different subroutine due to $AUTOLOAD
               changing its value.  Use the glob created via a
               side effect to do this.

               These functions have the same side-effects and as
               gv_fetchmeth with level==0.  name should be
               writable if contains ':' or '\''.  The warning
               against passing the GV returned by gv_fetchmeth to
               perl_call_sv apply equally to these functions.

                       GV*     gv_fetchmethod (HV* stash, char* name)
                       GV*     gv_fetchmethod_autoload (HV* stash, char* name, I32 autoload)

       G_VOID  Used to indicate void context.  See GIMME_V and
               the perlcall manpage.

       gv_stashpv
               Returns a pointer to the stash for a specified
               package.  If create is set then the package will
               be created if it does not already exist.  If
               create is not set and the package does not exist
               then NULL is returned.

                       HV*     gv_stashpv (char* name, I32 create)

       gv_stashsv
               Returns a pointer to the stash for a specified
               package.  See gv_stashpv.

                       HV*     gv_stashsv (SV* sv, I32 create)

       GvSV    Return the SV from the GV.

       HEf_SVKEY
               This flag, used in the length slot of hash entries
               and magic structures, specifies the structure
               contains a SV* pointer where a char* pointer is to
               be expected. (For information only--not to be
               used).

       HeHASH  Returns the computed hash stored in the hash
               entry.

                       U32     HeHASH(HE* he)

       HeKEY   Returns the actual pointer stored in the key slot
               of the hash entry.  The pointer may be either
               char* or SV*, depending on the value of HeKLEN().
               Can be assigned to.  The HePV() or HeSVKEY()
               macros are usually preferable for finding the
               value of a key.

                       char*   HeKEY(HE* he)

       HeKLEN  If this is negative, and amounts to HEf_SVKEY, it
               indicates the entry holds an SV* key.  Otherwise,
               holds the actual length of the key.  Can be
               assigned to. The HePV() macro is usually
               preferable for finding key lengths.

                       int     HeKLEN(HE* he)

       HePV    Returns the key slot of the hash entry as a char*
               value, doing any necessary dereferencing of
               possibly SV* keys.  The length of the string is
               placed in len (this is a macro, so do not use
               &len).  If you do not care about what the length
               of the key is, you may use the global variable
               PL_na, though this is rather less efficient than
               using a local variable.  Remember though, that
               hash keys in perl are free to contain embedded
               nulls, so using strlen() or similar is not a good
               way to find the length of hash keys.  This is very
               similar to the SvPV() macro described elsewhere in
               this document.

                       char*   HePV(HE* he, STRLEN len)

       HeSVKEY Returns the key as an SV*, or Nullsv if the hash
               entry does not contain an SV* key.

                       HeSVKEY(HE* he)

       HeSVKEY_force
               Returns the key as an SV*.  Will create and return
               a temporary mortal SV* if the hash entry contains
               only a char* key.

                       HeSVKEY_force(HE* he)

       HeSVKEY_set
               Sets the key to a given SV*, taking care to set
               the appropriate flags to indicate the presence of
               an SV* key, and returns the same SV*.

                       HeSVKEY_set(HE* he, SV* sv)

       HeVAL   Returns the value slot (type SV*) stored in the
               hash entry.

                       HeVAL(HE* he)

       hv_clear
               Clears a hash, making it empty.

                       void    hv_clear (HV* tb)

       hv_delete
               Deletes a key/value pair in the hash.  The value
               SV is removed from the hash and returned to the
               caller.  The klen is the length of the key.  The
               flags value will normally be zero; if set to
               G_DISCARD then NULL will be returned.

                       SV*     hv_delete (HV* tb, char* key, U32 klen, I32 flags)

       hv_delete_ent
               Deletes a key/value pair in the hash.  The value
               SV is removed from the hash and returned to the
               caller.  The flags value will normally be zero; if
               set to G_DISCARD then NULL will be returned.  hash
               can be a valid precomputed hash value, or 0 to ask
               for it to be computed.

                       SV*     hv_delete_ent (HV* tb, SV* key, I32 flags, U32 hash)

       hv_exists
               Returns a boolean indicating whether the specified
               hash key exists.  The klen is the length of the
               key.

                       bool    hv_exists (HV* tb, char* key, U32 klen)

       hv_exists_ent
               Returns a boolean indicating whether the specified
               hash key exists. hash can be a valid precomputed
               hash value, or 0 to ask for it to be computed.

                       bool    hv_exists_ent (HV* tb, SV* key, U32 hash)

       hv_fetch
               Returns the SV which corresponds to the specified
               key in the hash.  The klen is the length of the
               key.  If lval is set then the fetch will be part
               of a store.  Check that the return value is non-
               null before dereferencing it to a SV*.

               See the section on Understanding the Magic of Tied
               Hashes and Arrays for more information on how to
               use this function on tied hashes.

                       SV**    hv_fetch (HV* tb, char* key, U32 klen, I32 lval)

       hv_fetch_ent
               Returns the hash entry which corresponds to the
               specified key in the hash.  hash must be a valid
               precomputed hash number for the given key, or 0 if
               you want the function to compute it.  IF lval is
               set then the fetch will be part of a store.  Make
               sure the return value is non-null before accessing
               it.  The return value when tb is a tied hash is a
               pointer to a static location, so be sure to make a
               copy of the structure if you need to store it
               somewhere.

               See the section on Understanding the Magic of Tied
               Hashes and Arrays for more information on how to
               use this function on tied hashes.

                       HE*     hv_fetch_ent  (HV* tb, SV* key, I32 lval, U32 hash)

       hv_iterinit
               Prepares a starting point to traverse a hash
               table.

                       I32     hv_iterinit (HV* tb)

               Returns the number of keys in the hash (i.e. the
               same as HvKEYS(tb)).  The return value is
               currently only meaningful for hashes without tie
               magic.

               NOTE: Before version 5.004_65, hv_iterinit used to
               return the number of hash buckets that happen to
               be in use.  If you still need that esoteric value,
               you can get it through the macro HvFILL(tb).

       hv_iterkey
               Returns the key from the current position of the
               hash iterator.  See hv_iterinit.

                       char*   hv_iterkey (HE* entry, I32* retlen)

       hv_iterkeysv
               Returns the key as an SV* from the current
               position of the hash iterator.  The return value
               will always be a mortal copy of the key.  Also see
               hv_iterinit.

                       SV*     hv_iterkeysv  (HE* entry)

       hv_iternext
               Returns entries from a hash iterator.  See
               hv_iterinit.

                       HE*     hv_iternext (HV* tb)

       hv_iternextsv
               Performs an hv_iternext, hv_iterkey, and
               hv_iterval in one operation.

                       SV*     hv_iternextsv (HV* hv, char** key, I32* retlen)

       hv_iterval
               Returns the value from the current position of the
               hash iterator.  See hv_iterkey.

                       SV*     hv_iterval (HV* tb, HE* entry)

       hv_magic
               Adds magic to a hash.  See sv_magic.

                       void    hv_magic (HV* hv, GV* gv, int how)

       HvNAME  Returns the package name of a stash.  See SvSTASH,
               CvSTASH.

                       char*   HvNAME (HV* stash)

       hv_store
               Stores an SV in a hash.  The hash key is specified
               as key and klen is the length of the key.  The
               hash parameter is the precomputed hash value; if
               it is zero then Perl will compute it.  The return
               value will be NULL if the operation failed or if
               the value did not need to be actually stored
               within the hash (as in the case of tied hashes).
               Otherwise it can be dereferenced to get the
               original SV*.  Note that the caller is responsible
               for suitably incrementing the reference count of
               val before the call, and decrementing it if the
               function returned NULL.

               See the section on Understanding the Magic of Tied
               Hashes and Arrays for more information on how to
               use this function on tied hashes.

                       SV**    hv_store (HV* tb, char* key, U32 klen, SV* val, U32 hash)

       hv_store_ent
               Stores val in a hash.  The hash key is specified
               as key.  The hash parameter is the precomputed
               hash value; if it is zero then Perl will compute
               it.  The return value is the new hash entry so
               created.  It will be NULL if the operation failed
               or if the value did not need to be actually stored
               within the hash (as in the case of tied hashes).
               Otherwise the contents of the return value can be
               accessed using the He??? macros described here.
               Note that the caller is responsible for suitably
               incrementing the reference count of val before the
               call, and decrementing it if the function returned
               NULL.

               See the section on Understanding the Magic of Tied
               Hashes and Arrays for more information on how to
               use this function on tied hashes.

                       HE*     hv_store_ent  (HV* tb, SV* key, SV* val, U32 hash)

       hv_undef
               Undefines the hash.

                       void    hv_undef (HV* tb)

       isALNUM Returns a boolean indicating whether the C char is
               an ascii alphanumeric character or digit.

                       int     isALNUM (char c)

       isALPHA Returns a boolean indicating whether the C char is
               an ascii alphabetic character.

                       int     isALPHA (char c)

       isDIGIT Returns a boolean indicating whether the C char is
               an ascii digit.

                       int     isDIGIT (char c)

       isLOWER Returns a boolean indicating whether the C char is
               a lowercase character.

                       int     isLOWER (char c)

       isSPACE Returns a boolean indicating whether the C char is
               whitespace.

                       int     isSPACE (char c)

       isUPPER Returns a boolean indicating whether the C char is
               an uppercase character.

                       int     isUPPER (char c)

       items   Variable which is setup by xsubpp to indicate the
               number of items on the stack.  See the section on
               Variable-length Parameter Lists in the perlxs
               manpage.

       ix      Variable which is setup by xsubpp to indicate
               which of an XSUB's aliases was used to invoke it.
               See the section on The ALIAS: Keyword in the
               perlxs manpage.

       LEAVE   Closing bracket on a callback.  See ENTER and the
               perlcall manpage.

                       LEAVE;

       looks_like_number
               Test if an the content of an SV looks like a
               number (or is a number).

                       int     looks_like_number(SV*)

       MARK    Stack marker variable for the XSUB.  See dMARK.

       mg_clear
               Clear something magical that the SV represents.
               See sv_magic.

                       int     mg_clear (SV* sv)

       mg_copy Copies the magic from one SV to another.  See
               sv_magic.

                       int     mg_copy (SV *, SV *, char *, STRLEN)

       mg_find Finds the magic pointer for type matching the SV.
               See sv_magic.

                       MAGIC*  mg_find (SV* sv, int type)

       mg_free Free any magic storage used by the SV.  See
               sv_magic.

                       int     mg_free (SV* sv)

       mg_get  Do magic after a value is retrieved from the SV.
               See sv_magic.

                       int     mg_get (SV* sv)

       mg_len  Report on the SV's length.  See sv_magic.

                       U32     mg_len (SV* sv)

       mg_magical
               Turns on the magical status of an SV.  See
               sv_magic.

                       void    mg_magical (SV* sv)

       mg_set  Do magic after a value is assigned to the SV.  See
               sv_magic.

                       int     mg_set (SV* sv)

       modglobal
               modglobal is a general purpose, interpreter global
               HV for use by extensions that need to keep
               information on a per-interpreter basis.  In a
               pinch, it can also be used as a symbol table for
               extensions to share data among each other.  It is
               a good idea to use keys prefixed by the package
               name of the extension that owns the data.

       Move    The XSUB-writer's interface to the C memmove
               function.  The s is the source, d is the
               destination, n is the number of items, and t is
               the type.  Can do overlapping moves.  See also
               Copy.

                       void    Move( s, d, n, t )

       PL_na   A convenience variable which is typically used
               with SvPV when one doesn't care about the length
               of the string.  It is usually more efficient to
               declare a local variable and use that instead.

       New     The XSUB-writer's interface to the C malloc
               function.

                       void*   New( x, void *ptr, int size, type )

       newAV   Creates a new AV.  The reference count is set to
               1.

                       AV*     newAV (void)

       Newc    The XSUB-writer's interface to the C malloc
               function, with cast.

                       void*   Newc( x, void *ptr, int size, type, cast )

       newCONSTSUB
               Creates a constant sub equivalent to Perl sub FOO
               () { 123 } which is eligible for inlining at
               compile-time.

                       void    newCONSTSUB(HV* stash, char* name, SV* sv)

       newHV   Creates a new HV.  The reference count is set to
               1.

                       HV*     newHV (void)

       newRV_inc
               Creates an RV wrapper for an SV.  The reference
               count for the original SV is incremented.

                       SV*     newRV_inc (SV* ref)

               For historical reasons, "newRV" is a synonym for
               "newRV_inc".

       newRV_noinc
               Creates an RV wrapper for an SV.  The reference
               count for the original SV is nnoott incremented.

                       SV*     newRV_noinc (SV* ref)

       NEWSV   Creates a new SV.  A non-zero len parameter
               indicates the number of bytes of preallocated
               string space the SV should have.  An extra byte
               for a tailing NUL is also reserved.  (SvPOK is not
               set for the SV even if string space is allocated.)
               The reference count for the new SV is set to 1.
               id is an integer id between 0 and 1299 (used to
               identify leaks).

                       SV*     NEWSV (int id, STRLEN len)

       newSViv Creates a new SV and copies an integer into it.
               The reference count for the SV is set to 1.

                       SV*     newSViv (IV i)

       newSVnv Creates a new SV and copies a double into it.  The
               reference count for the SV is set to 1.

                       SV*     newSVnv (NV i)

       newSVpv Creates a new SV and copies a string into it.  The
               reference count for the SV is set to 1.  If len is
               zero then Perl will compute the length.

                       SV*     newSVpv (char* s, STRLEN len)

       newSVpvf
               Creates a new SV an initialize it with the string
               formatted like sprintf.

                       SV*     newSVpvf(const char* pat, ...);

       newSVpvn
               Creates a new SV and copies a string into it.  The
               reference count for the SV is set to 1.  If len is
               zero then Perl will create a zero length string.

                       SV*     newSVpvn (char* s, STRLEN len)

       newSVrv Creates a new SV for the RV, rv, to point to.  If
               rv is not an RV then it will be upgraded to one.
               If classname is non-null then the new SV will be
               blessed in the specified package.  The new SV is
               returned and its reference count is 1.

                       SV*     newSVrv (SV* rv, char* classname)

       newSVsv Creates a new SV which is an exact duplicate of
               the original SV.

                       SV*     newSVsv (SV* old)

       newXS   Used by xsubpp to hook up XSUBs as Perl subs.

       newXSproto
               Used by xsubpp to hook up XSUBs as Perl subs.
               Adds Perl prototypes to the subs.

       Newz    The XSUB-writer's interface to the C malloc
               function.  The allocated memory is zeroed with
               memzero.

                       void*   Newz( x, void *ptr, int size, type )

       Nullav  Null AV pointer.

       Nullch  Null character pointer.

       Nullcv  Null CV pointer.

       Nullhv  Null HV pointer.

       Nullsv  Null SV pointer.

       ORIGMARK
               The original stack mark for the XSUB.  See
               dORIGMARK.

       perl_alloc
               Allocates a new Perl interpreter.  See the
               perlembed manpage.

       perl_call_argv
               Performs a callback to the specified Perl sub.
               See the perlcall manpage.

                       I32     perl_call_argv (char* subname, I32 flags, char** argv)

       perl_call_method
               Performs a callback to the specified Perl method.
               The blessed object must be on the stack.  See the
               perlcall manpage.

                       I32     perl_call_method (char* methname, I32 flags)

       perl_call_pv
               Performs a callback to the specified Perl sub.
               See the perlcall manpage.

                       I32     perl_call_pv (char* subname, I32 flags)

       perl_call_sv
               Performs a callback to the Perl sub whose name is
               in the SV.  See the perlcall manpage.

                       I32     perl_call_sv (SV* sv, I32 flags)

       perl_construct
               Initializes a new Perl interpreter.  See the
               perlembed manpage.

       perl_destruct
               Shuts down a Perl interpreter.  See the perlembed
               manpage.

       perl_eval_sv
               Tells Perl to eval the string in the SV.

                       I32     perl_eval_sv (SV* sv, I32 flags)

       perl_eval_pv
               Tells Perl to eval the given string and return an
               SV* result.

                       SV*     perl_eval_pv (char* p, I32 croak_on_error)

       perl_free
               Releases a Perl interpreter.  See the perlembed
               manpage.

       perl_get_av
               Returns the AV of the specified Perl array.  If
               create is set and the Perl variable does not exist
               then it will be created.  If create is not set and
               the variable does not exist then NULL is returned.

                       AV*     perl_get_av (char* name, I32 create)

       perl_get_cv
               Returns the CV of the specified Perl sub.  If
               create is set and the Perl variable does not exist
               then it will be created.  If create is not set and
               the variable does not exist then NULL is returned.

                       CV*     perl_get_cv (char* name, I32 create)

       perl_get_hv
               Returns the HV of the specified Perl hash.  If
               create is set and the Perl variable does not exist
               then it will be created.  If create is not set and
               the variable does not exist then NULL is returned.

                       HV*     perl_get_hv (char* name, I32 create)

       perl_get_sv
               Returns the SV of the specified Perl scalar.  If
               create is set and the Perl variable does not exist
               then it will be created.  If create is not set and
               the variable does not exist then NULL is returned.

                       SV*     perl_get_sv (char* name, I32 create)

       perl_parse
               Tells a Perl interpreter to parse a Perl script.
               See the perlembed manpage.

       perl_require_pv
               Tells Perl to require a module.

                       void    perl_require_pv (char* pv)

       perl_run
               Tells a Perl interpreter to run.  See the
               perlembed manpage.

       POPi    Pops an integer off the stack.

                       int     POPi()

       POPl    Pops a long off the stack.

                       long    POPl()

       POPp    Pops a string off the stack.

                       char*   POPp()

       POPn    Pops a double off the stack.

                       double  POPn()

       POPs    Pops an SV off the stack.

                       SV*     POPs()

       PUSHMARK
               Opening bracket for arguments on a callback.  See
               PUTBACK and the perlcall manpage.

                       PUSHMARK(p)

       PUSHi   Push an integer onto the stack.  The stack must
               have room for this element.  Handles 'set' magic.
               See XPUSHi.

                       void    PUSHi(int d)

       PUSHn   Push a double onto the stack.  The stack must have
               room for this element.  Handles 'set' magic.  See
               XPUSHn.

                       void    PUSHn(double d)

       PUSHp   Push a string onto the stack.  The stack must have
               room for this element.  The len indicates the
               length of the string.  Handles 'set' magic.  See
               XPUSHp.

                       void    PUSHp(char *c, int len )

       PUSHs   Push an SV onto the stack.  The stack must have
               room for this element.  Does not handle 'set'
               magic.  See XPUSHs.

                       void    PUSHs(sv)

       PUSHu   Push an unsigned integer onto the stack.  The
               stack must have room for this element.  See
               XPUSHu.

                       void    PUSHu(unsigned int d)

       PUTBACK Closing bracket for XSUB arguments.  This is
               usually handled by xsubpp.  See PUSHMARK and the
               perlcall manpage for other uses.

                       PUTBACK;

       Renew   The XSUB-writer's interface to the C realloc
               function.

                       void*   Renew( void *ptr, int size, type )

       Renewc  The XSUB-writer's interface to the C realloc
               function, with cast.

                       void*   Renewc( void *ptr, int size, type, cast )

       RETVAL  Variable which is setup by xsubpp to hold the
               return value for an XSUB.  This is always the
               proper type for the XSUB.  See the section on The
               RETVAL Variable in the perlxs manpage.

       safefree
               The XSUB-writer's interface to the C free
               function.

       safemalloc
               The XSUB-writer's interface to the C malloc
               function.

       saferealloc
               The XSUB-writer's interface to the C realloc
               function.

       savepv  Copy a string to a safe spot.  This does not use
               an SV.

                       char*   savepv (char* sv)

       savepvn Copy a string to a safe spot.  The len indicates
               number of bytes to copy.  This does not use an SV.

                       char*   savepvn (char* sv, I32 len)

       SAVETMPS
               Opening bracket for temporaries on a callback.
               See FREETMPS and the perlcall manpage.

                       SAVETMPS;

       SP      Stack pointer.  This is usually handled by xsubpp.
               See dSP and SPAGAIN.

       SPAGAIN Refetch the stack pointer.  Used after a callback.
               See the perlcall manpage.

                       SPAGAIN;

       ST      Used to access elements on the XSUB's stack.

                       SV*     ST(int x)

       strEQ   Test two strings to see if they are equal.
               Returns true or false.

                       int     strEQ( char *s1, char *s2 )

       strGE   Test two strings to see if the first, s1, is
               greater than or equal to the second, s2.  Returns
               true or false.

                       int     strGE( char *s1, char *s2 )

       strGT   Test two strings to see if the first, s1, is
               greater than the second, s2.  Returns true or
               false.

                       int     strGT( char *s1, char *s2 )

       strLE   Test two strings to see if the first, s1, is less
               than or equal to the second, s2.  Returns true or
               false.

                       int     strLE( char *s1, char *s2 )

       strLT   Test two strings to see if the first, s1, is less
               than the second, s2.  Returns true or false.

                       int     strLT( char *s1, char *s2 )

       strNE   Test two strings to see if they are different.
               Returns true or false.

                       int     strNE( char *s1, char *s2 )

       strnEQ  Test two strings to see if they are equal.  The
               len parameter indicates the number of bytes to
               compare.  Returns true or false.

                       int     strnEQ( char *s1, char *s2 )

       strnNE  Test two strings to see if they are different.
               The len parameter indicates the number of bytes to
               compare.  Returns true or false.

                       int     strnNE( char *s1, char *s2, int len )

       sv_2mortal
               Marks an SV as mortal.  The SV will be destroyed
               when the current context ends.

                       SV*     sv_2mortal (SV* sv)

       sv_bless
               Blesses an SV into a specified package.  The SV
               must be an RV.  The package must be designated by
               its stash (see gv_stashpv()).  The reference count
               of the SV is unaffected.

                       SV*     sv_bless (SV* sv, HV* stash)

       sv_catpv
               Concatenates the string onto the end of the string
               which is in the SV.  Handles 'get' magic, but not
               'set' magic.  See sv_catpv_mg.

                       void    sv_catpv (SV* sv, char* ptr)

       sv_catpv_mg
               Like sv_catpv, but also handles 'set' magic.

                       void    sv_catpv_mg (SV* sv, const char* ptr)

       sv_catpvn
               Concatenates the string onto the end of the string
               which is in the SV.  The len indicates number of
               bytes to copy.  Handles 'get' magic, but not 'set'
               magic.  See sv_catpvn_mg.

                       void    sv_catpvn (SV* sv, char* ptr, STRLEN len)

       sv_catpvn_mg
               Like sv_catpvn, but also handles 'set' magic.

                       void    sv_catpvn_mg (SV* sv, char* ptr, STRLEN len)

       sv_catpvf
               Processes its arguments like sprintf and appends
               the formatted output to an SV.  Handles 'get'
               magic, but not 'set' magic.  SvSETMAGIC() must
               typically be called after calling this function to
               handle 'set' magic.

                       void    sv_catpvf (SV* sv, const char* pat, ...)

       sv_catpvf_mg
               Like sv_catpvf, but also handles 'set' magic.

                       void    sv_catpvf_mg (SV* sv, const char* pat, ...)

       sv_catsv
               Concatenates the string from SV ssv onto the end
               of the string in SV dsv.  Handles 'get' magic, but
               not 'set' magic.  See sv_catsv_mg.

                       void    sv_catsv (SV* dsv, SV* ssv)

       sv_catsv_mg
               Like sv_catsv, but also handles 'set' magic.

                       void    sv_catsv_mg (SV* dsv, SV* ssv)

       sv_chop Efficient removal of characters from the beginning
               of the string buffer.  SvPOK(sv) must be true and
               the ptr must be a pointer to somewhere inside the
               string buffer.  The ptr becomes the first
               character of the adjusted string.

                       void    sv_chop(SV* sv, char *ptr)

       sv_cmp  Compares the strings in two SVs.  Returns -1, 0,
               or 1 indicating whether the string in sv1 is less
               than, equal to, or greater than the string in sv2.

                       I32     sv_cmp (SV* sv1, SV* sv2)

       SvCUR   Returns the length of the string which is in the
               SV.  See SvLEN.

                       int     SvCUR (SV* sv)

       SvCUR_set
               Set the length of the string which is in the SV.
               See SvCUR.

                       void    SvCUR_set (SV* sv, int val)

       sv_dec  Auto-decrement of the value in the SV.

                       void    sv_dec (SV* sv)

       sv_derived_from
               Returns a boolean indicating whether the SV is
               derived from the specified class.  This is the
               function that implements UNIVERSAL::isa.  It works
               for class names as well as for objects.

                       bool    sv_derived_from _((SV* sv, char* name));

       SvEND   Returns a pointer to the last character in the
               string which is in the SV.  See SvCUR.  Access the
               character as

                       char*   SvEND(sv)

       sv_eq   Returns a boolean indicating whether the strings
               in the two SVs are identical.

                       I32     sv_eq (SV* sv1, SV* sv2)

       SvGETMAGIC
               Invokes mg_get on an SV if it has 'get' magic.
               This macro evaluates its argument more than once.

                       void    SvGETMAGIC(SV *sv)

       SvGROW  Expands the character buffer in the SV so that it
               has room for the indicated number of bytes
               (remember to reserve space for an extra trailing
               NUL character).  Calls sv_grow to perform the
               expansion if necessary.  Returns a pointer to the
               character buffer.

                       char*   SvGROW(SV* sv, STRLEN len)

       sv_grow Expands the character buffer in the SV.  This will
               use sv_unref and will upgrade the SV to SVt_PV.
               Returns a pointer to the character buffer.  Use
               SvGROW.

       sv_inc  Auto-increment of the value in the SV.

                       void    sv_inc (SV* sv)

       sv_insert
               Inserts a string at the specified offset/length
               within the SV.  Similar to the Perl substr()
               function.

                       void    sv_insert(SV *sv, STRLEN offset, STRLEN len,
                                         char *str, STRLEN strlen)

       SvIOK   Returns a boolean indicating whether the SV
               contains an integer.

                       int     SvIOK (SV* SV)

       SvIOK_off
               Unsets the IV status of an SV.

                       void    SvIOK_off (SV* sv)

       SvIOK_on
               Tells an SV that it is an integer.

                       void    SvIOK_on (SV* sv)

       SvIOK_only
               Tells an SV that it is an integer and disables all
               other OK bits.

                       void    SvIOK_only (SV* sv)

       SvIOKp  Returns a boolean indicating whether the SV
               contains an integer.  Checks the pprriivvaattee setting.
               Use SvIOK.

                       int     SvIOKp (SV* SV)

       sv_isa  Returns a boolean indicating whether the SV is
               blessed into the specified class.  This does not
               check for subtypes; use sv_derived_from to verify
               an inheritance relationship.

                       int     sv_isa (SV* sv, char* name)

       sv_isobject
               Returns a boolean indicating whether the SV is an
               RV pointing to a blessed object.  If the SV is not
               an RV, or if the object is not blessed, then this
               will return false.

                       int     sv_isobject (SV* sv)

       SvIV    Coerces the given SV to an integer and returns it.

                       int SvIV (SV* sv)

       SvIVX   Returns the integer which is stored in the SV,
               assuming SvIOK is true.

                       int     SvIVX (SV* sv)

       SvLEN   Returns the size of the string buffer in the SV.
               See SvCUR.

                       int     SvLEN (SV* sv)

       sv_len  Returns the length of the string in the SV.  Use
               SvCUR.

                       STRLEN  sv_len (SV* sv)

       sv_magic
               Adds magic to an SV.

                       void    sv_magic (SV* sv, SV* obj, int how, char* name, I32 namlen)

       sv_mortalcopy
               Creates a new SV which is a copy of the original
               SV.  The new SV is marked as mortal.

                       SV*     sv_mortalcopy (SV* oldsv)

       sv_newmortal
               Creates a new SV which is mortal.  The reference
               count of the SV is set to 1.

                       SV*     sv_newmortal (void)

       SvNIOK  Returns a boolean indicating whether the SV
               contains a number, integer or double.

                       int     SvNIOK (SV* SV)

       SvNIOK_off
               Unsets the NV/IV status of an SV.

                       void    SvNIOK_off (SV* sv)

       SvNIOKp Returns a boolean indicating whether the SV
               contains a number, integer or double.  Checks the
               pprriivvaattee setting.  Use SvNIOK.

                       int     SvNIOKp (SV* SV)

       PL_sv_no
               This is the false SV.  See PL_sv_yes.  Always
               refer to this as &PL_sv_no.

       SvNOK   Returns a boolean indicating whether the SV
               contains a double.

                       int     SvNOK (SV* SV)

       SvNOK_off
               Unsets the NV status of an SV.

                       void    SvNOK_off (SV* sv)

       SvNOK_on
               Tells an SV that it is a double.

                       void    SvNOK_on (SV* sv)

       SvNOK_only
               Tells an SV that it is a double and disables all
               other OK bits.

                       void    SvNOK_only (SV* sv)

       SvNOKp  Returns a boolean indicating whether the SV
               contains a double.  Checks the pprriivvaattee setting.
               Use SvNOK.

                       int     SvNOKp (SV* SV)

       SvNV    Coerce the given SV to a double and return it.

                       double  SvNV (SV* sv)

       SvNVX   Returns the double which is stored in the SV,
               assuming SvNOK is true.

                       double  SvNVX (SV* sv)

       SvOK    Returns a boolean indicating whether the value is
               an SV.

                       int     SvOK (SV* sv)

       SvOOK   Returns a boolean indicating whether the SvIVX is
               a valid offset value for the SvPVX.  This hack is
               used internally to speed up removal of characters
               from the beginning of a SvPV.  When SvOOK is true,
               then the start of the allocated string buffer is
               really (SvPVX - SvIVX).

                       int     SvOOK(SV* sv)

       SvPOK   Returns a boolean indicating whether the SV
               contains a character string.

                       int     SvPOK (SV* SV)

       SvPOK_off
               Unsets the PV status of an SV.

                       void    SvPOK_off (SV* sv)

       SvPOK_on
               Tells an SV that it is a string.

                       void    SvPOK_on (SV* sv)

       SvPOK_only
               Tells an SV that it is a string and disables all
               other OK bits.

                       void    SvPOK_only (SV* sv)

       SvPOKp  Returns a boolean indicating whether the SV
               contains a character string.  Checks the pprriivvaattee
               setting.  Use SvPOK.

                       int     SvPOKp (SV* SV)

       SvPV    Returns a pointer to the string in the SV, or a
               stringified form of the SV if the SV does not
               contain a string.  Handles 'get' magic.

                       char*   SvPV (SV* sv, STRLEN len)

       SvPV_force
               Like <SvPV> but will force the SV into becoming a
               string (SvPOK).  You want force if you are going
               to update the SvPVX directly.

                       char*   SvPV_force(SV* sv, STRLEN len)

       SvPVX   Returns a pointer to the string in the SV.  The SV
               must contain a string.

                       char*   SvPVX (SV* sv)

       SvREFCNT
               Returns the value of the object's reference count.

                       int     SvREFCNT (SV* sv)

       SvREFCNT_dec
               Decrements the reference count of the given SV.

                       void    SvREFCNT_dec (SV* sv)

       SvREFCNT_inc
               Increments the reference count of the given SV.

                       void    SvREFCNT_inc (SV* sv)

       SvROK   Tests if the SV is an RV.

                       int     SvROK (SV* sv)

       SvROK_off
               Unsets the RV status of an SV.

                       void    SvROK_off (SV* sv)

       SvROK_on
               Tells an SV that it is an RV.

                       void    SvROK_on (SV* sv)

       SvRV    Dereferences an RV to return the SV.

                       SV*     SvRV (SV* sv)

       SvSETMAGIC
               Invokes mg_set on an SV if it has 'set' magic.
               This macro evaluates its argument more than once.

                       void    SvSETMAGIC( SV *sv )

       sv_setiv
               Copies an integer into the given SV.  Does not
               handle 'set' magic.  See sv_setiv_mg.

                       void    sv_setiv (SV* sv, IV num)

       sv_setiv_mg
               Like sv_setiv, but also handles 'set' magic.

                       void    sv_setiv_mg (SV* sv, IV num)

       sv_setnv
               Copies a double into the given SV.  Does not
               handle 'set' magic.  See sv_setnv_mg.

                       void    sv_setnv (SV* sv, double num)

       sv_setnv_mg
               Like sv_setnv, but also handles 'set' magic.

                       void    sv_setnv_mg (SV* sv, double num)

       sv_setpv
               Copies a string into an SV.  The string must be
               null-terminated.  Does not handle 'set' magic.
               See sv_setpv_mg.

                       void    sv_setpv (SV* sv, const char* ptr)

       sv_setpv_mg
               Like sv_setpv, but also handles 'set' magic.

                       void    sv_setpv_mg (SV* sv, const char* ptr)

       sv_setpviv
               Copies an integer into the given SV, also updating
               its string value.  Does not handle 'set' magic.
               See sv_setpviv_mg.

                       void    sv_setpviv (SV* sv, IV num)

       sv_setpviv_mg
               Like sv_setpviv, but also handles 'set' magic.

                       void    sv_setpviv_mg (SV* sv, IV num)

       sv_setpvn
               Copies a string into an SV.  The len parameter
               indicates the number of bytes to be copied.  Does
               not handle 'set' magic.  See sv_setpvn_mg.

                       void    sv_setpvn (SV* sv, const char* ptr, STRLEN len)

       sv_setpvn_mg
               Like sv_setpvn, but also handles 'set' magic.

                       void    sv_setpvn_mg (SV* sv, const char* ptr, STRLEN len)

       sv_setpvf
               Processes its arguments like sprintf and sets an
               SV to the formatted output.  Does not handle 'set'
               magic.  See sv_setpvf_mg.

                       void    sv_setpvf (SV* sv, const char* pat, ...)

       sv_setpvf_mg
               Like sv_setpvf, but also handles 'set' magic.

                       void    sv_setpvf_mg (SV* sv, const char* pat, ...)

       sv_setref_iv
               Copies an integer into a new SV, optionally
               blessing the SV.  The rv argument will be upgraded
               to an RV.  That RV will be modified to point to
               the new SV.  The classname argument indicates the
               package for the blessing.  Set classname to Nullch
               to avoid the blessing.  The new SV will be
               returned and will have a reference count of 1.

                       SV*     sv_setref_iv (SV *rv, char *classname, IV iv)

       sv_setref_nv
               Copies a double into a new SV, optionally blessing
               the SV.  The rv argument will be upgraded to an
               RV.  That RV will be modified to point to the new
               SV.  The classname argument indicates the package
               for the blessing.  Set classname to Nullch to
               avoid the blessing.  The new SV will be returned
               and will have a reference count of 1.

                       SV*     sv_setref_nv (SV *rv, char *classname, double nv)

       sv_setref_pv
               Copies a pointer into a new SV, optionally
               blessing the SV.  The rv argument will be upgraded
               to an RV.  That RV will be modified to point to
               the new SV.  If the pv argument is NULL then
               PL_sv_undef will be placed into the SV.  The
               classname argument indicates the package for the
               blessing.  Set classname to Nullch to avoid the
               blessing.  The new SV will be returned and will
               have a reference count of 1.

                       SV*     sv_setref_pv (SV *rv, char *classname, void* pv)

               Do not use with integral Perl types such as HV,
               AV, SV, CV, because those objects will become
               corrupted by the pointer copy process.

               Note that sv_setref_pvn copies the string while
               this copies the pointer.

       sv_setref_pvn
               Copies a string into a new SV, optionally blessing
               the SV.  The length of the string must be
               specified with n.  The rv argument will be
               upgraded to an RV.  That RV will be modified to
               point to the new SV.  The classname argument
               indicates the package for the blessing.  Set
               classname to Nullch to avoid the blessing.  The
               new SV will be returned and will have a reference
               count of 1.

                       SV*     sv_setref_pvn (SV *rv, char *classname, char* pv, I32 n)

               Note that sv_setref_pv copies the pointer while
               this copies the string.

       SvSetSV Calls sv_setsv if dsv is not the same as ssv.  May
               evaluate arguments more than once.

                       void    SvSetSV (SV* dsv, SV* ssv)

       SvSetSV_nosteal
               Calls a non-destructive version of sv_setsv if dsv
               is not the same as ssv.  May evaluate arguments
               more than once.

                       void    SvSetSV_nosteal (SV* dsv, SV* ssv)

       sv_setsv
               Copies the contents of the source SV ssv into the
               destination SV dsv.  The source SV may be
               destroyed if it is mortal.  Does not handle 'set'
               magic.  See the macro forms SvSetSV,
               SvSetSV_nosteal and sv_setsv_mg.

                       void    sv_setsv (SV* dsv, SV* ssv)

       sv_setsv_mg
               Like sv_setsv, but also handles 'set' magic.

                       void    sv_setsv_mg (SV* dsv, SV* ssv)

       sv_setuv
               Copies an unsigned integer into the given SV.
               Does not handle 'set' magic.  See sv_setuv_mg.

                       void    sv_setuv (SV* sv, UV num)

       sv_setuv_mg
               Like sv_setuv, but also handles 'set' magic.

                       void    sv_setuv_mg (SV* sv, UV num)

       SvSTASH Returns the stash of the SV.

                       HV*     SvSTASH (SV* sv)

       SvTAINT Taints an SV if tainting is enabled

                       void    SvTAINT (SV* sv)

       SvTAINTED
               Checks to see if an SV is tainted. Returns TRUE if
               it is, FALSE if not.

                       int     SvTAINTED (SV* sv)

       SvTAINTED_off
               Untaints an SV. Be very careful with this routine,
               as it short-circuits some of Perl's fundamental
               security features. XS module authors should not
               use this function unless they fully understand all
               the implications of unconditionally untainting the
               value. Untainting should be done in the standard
               perl fashion, via a carefully crafted regexp,
               rather than directly untainting variables.

                       void    SvTAINTED_off (SV* sv)

       SvTAINTED_on
               Marks an SV as tainted.

                       void    SvTAINTED_on (SV* sv)

       SVt_IV  Integer type flag for scalars.  See svtype.

       SVt_PV  Pointer type flag for scalars.  See svtype.

       SVt_PVAV
               Type flag for arrays.  See svtype.

       SVt_PVCV
               Type flag for code refs.  See svtype.

       SVt_PVHV
               Type flag for hashes.  See svtype.

       SVt_PVMG
               Type flag for blessed scalars.  See svtype.

       SVt_NV  Double type flag for scalars.  See svtype.

       SvTRUE  Returns a boolean indicating whether Perl would
               evaluate the SV as true or false, defined or
               undefined.  Does not handle 'get' magic.

                       int     SvTRUE (SV* sv)

       SvTYPE  Returns the type of the SV.  See svtype.

                       svtype  SvTYPE (SV* sv)

       svtype  An enum of flags for Perl types.  These are found
               in the file ssvv..hh in the svtype enum.  Test these
               flags with the SvTYPE macro.

       PL_sv_undef
               This is the undef SV.  Always refer to this as
               &PL_sv_undef.

       sv_unref
               Unsets the RV status of the SV, and decrements the
               reference count of whatever was being referenced
               by the RV.  This can almost be thought of as a
               reversal of newSVrv.  See SvROK_off.

                       void    sv_unref (SV* sv)

       SvUPGRADE
               Used to upgrade an SV to a more complex form.
               Uses sv_upgrade to perform the upgrade if
               necessary.  See svtype.

                       bool    SvUPGRADE (SV* sv, svtype mt)

       sv_upgrade
               Upgrade an SV to a more complex form.  Use
               SvUPGRADE.  See svtype.

       sv_usepvn
               Tells an SV to use ptr to find its string value.
               Normally the string is stored inside the SV but
               sv_usepvn allows the SV to use an outside string.
               The ptr should point to memory that was allocated
               by malloc.  The string length, len, must be
               supplied.  This function will realloc the memory
               pointed to by ptr, so that pointer should not be
               freed or used by the programmer after giving it to
               sv_usepvn.  Does not handle 'set' magic.  See
               sv_usepvn_mg.

                       void    sv_usepvn (SV* sv, char* ptr, STRLEN len)

       sv_usepvn_mg
               Like sv_usepvn, but also handles 'set' magic.

                       void    sv_usepvn_mg (SV* sv, char* ptr, STRLEN len)

       sv_vcatpvfn(sv, pat, patlen, args, svargs, svmax,
               used_locale)
               Processes its arguments like vsprintf and appends
               the formatted output to an SV.  Uses an array of
               SVs if the C style variable argument list is
               missing (NULL).  Indicates if locale information
               has been used for formatting.

                       void    sv_catpvfn _((SV* sv, const char* pat, STRLEN patlen,
                                             va_list *args, SV **svargs, I32 svmax,
                                             bool *used_locale));

       sv_vsetpvfn(sv, pat, patlen, args, svargs, svmax,
               used_locale)
               Works like vcatpvfn but copies the text into the
               SV instead of appending it.

                       void    sv_setpvfn _((SV* sv, const char* pat, STRLEN patlen,
                                             va_list *args, SV **svargs, I32 svmax,
                                             bool *used_locale));

       SvUV    Coerces the given SV to an unsigned integer and
               returns it.

                       UV      SvUV(SV* sv)

       SvUVX   Returns the unsigned integer which is stored in
               the SV, assuming SvIOK is true.

                       UV      SvUVX(SV* sv)

       PL_sv_yes
               This is the true SV.  See PL_sv_no.  Always refer
               to this as &PL_sv_yes.

       THIS    Variable which is setup by xsubpp to designate the
               object in a C++ XSUB.  This is always the proper
               type for the C++ object.  See CLASS and the
               section on Using XS With C++ in the perlxs
               manpage.

       toLOWER Converts the specified character to lowercase.

                       int     toLOWER (char c)

       toUPPER Converts the specified character to uppercase.

                       int     toUPPER (char c)

       warn    This is the XSUB-writer's interface to Perl's warn
               function.  Use this function the same way you use
               the C printf function.  See croak().

       XPUSHi  Push an integer onto the stack, extending the
               stack if necessary.  Handles 'set' magic. See
               PUSHi.

                       XPUSHi(int d)

       XPUSHn  Push a double onto the stack, extending the stack
               if necessary.  Handles 'set' magic.  See PUSHn.

                       XPUSHn(double d)

       XPUSHp  Push a string onto the stack, extending the stack
               if necessary.  The len indicates the length of the
               string.  Handles 'set' magic.  See PUSHp.

                       XPUSHp(char *c, int len)

       XPUSHs  Push an SV onto the stack, extending the stack if
               necessary.  Does not handle 'set' magic.  See
               PUSHs.

                       XPUSHs(sv)

       XPUSHu  Push an unsigned integer onto the stack, extending
               the stack if necessary.  See PUSHu.

       XS      Macro to declare an XSUB and its C parameter list.
               This is handled by xsubpp.

       XSRETURN
               Return from XSUB, indicating number of items on
               the stack.  This is usually handled by xsubpp.

                       XSRETURN(int x)

       XSRETURN_EMPTY
               Return an empty list from an XSUB immediately.

                       XSRETURN_EMPTY;

       XSRETURN_IV
               Return an integer from an XSUB immediately.  Uses
               XST_mIV.

                       XSRETURN_IV(IV v)

       XSRETURN_NO
               Return &PL_sv_no from an XSUB immediately.  Uses
               XST_mNO.

                       XSRETURN_NO;

       XSRETURN_NV
               Return an double from an XSUB immediately.  Uses
               XST_mNV.

                       XSRETURN_NV(NV v)

       XSRETURN_PV
               Return a copy of a string from an XSUB
               immediately.  Uses XST_mPV.

                       XSRETURN_PV(char *v)

       XSRETURN_UNDEF
               Return &PL_sv_undef from an XSUB immediately.
               Uses XST_mUNDEF.

                       XSRETURN_UNDEF;

       XSRETURN_YES
               Return &PL_sv_yes from an XSUB immediately.  Uses
               XST_mYES.

                       XSRETURN_YES;

       XST_mIV Place an integer into the specified position i on
               the stack.  The value is stored in a new mortal
               SV.

                       XST_mIV( int i, IV v )

       XST_mNV Place a double into the specified position i on
               the stack.  The value is stored in a new mortal
               SV.

                       XST_mNV( int i, NV v )

       XST_mNO Place &PL_sv_no into the specified position i on
               the stack.

                       XST_mNO( int i )

       XST_mPV Place a copy of a string into the specified
               position i on the stack.  The value is stored in a
               new mortal SV.

                       XST_mPV( int i, char *v )

       XST_mUNDEF
               Place &PL_sv_undef into the specified position i
               on the stack.

                       XST_mUNDEF( int i )

       XST_mYES
               Place &PL_sv_yes into the specified position i on
               the stack.

                       XST_mYES( int i )

       XS_VERSION
               The version identifier for an XS module.  This is
               usually handled automatically by
               ExtUtils::MakeMaker.  See XS_VERSION_BOOTCHECK.

       XS_VERSION_BOOTCHECK
               Macro to verify that a PM module's $VERSION
               variable matches the XS module's XS_VERSION
               variable.  This is usually handled automatically
               by xsubpp.  See the section on The VERSIONCHECK:
               Keyword in the perlxs manpage.

       Zero    The XSUB-writer's interface to the C memzero
               function.  The d is the destination, n is the
               number of items, and t is the type.

                       void    Zero( d, n, t )

AAUUTTHHOORRSS
       Until May 1997, this document was maintained by Jeff
       Okamoto <okamoto@corp.hp.com>.  It is now maintained as
       part of Perl itself.

       With lots of help and suggestions from Dean Roehrich,
       Malcolm Beattie, Andreas Koenig, Paul Hudson, Ilya
       Zakharevich, Paul Marquess, Neil Bowers, Matthew Green,
       Tim Bunce, Spider Boardman, Ulrich Pfeifer, Stephen
       McCamant, and Gurusamy Sarathy.

       API Listing originally by Dean Roehrich
       <roehrich@cray.com>.

27/Mar/1999            perl 5.005, patch 03                     1