form_field(3X)                                     form_field(3X)

NAME
       form_fieldtype - define validation-field types

SYNOPSIS
       #include <form.h>
       FIELDTYPE *new_fieldtype(
           bool (* const field_check)(FIELD *, const void *),
           bool (* const char_check)(int, const void *));
       int free_fieldtype(FIELDTYPE *fieldtype);
       int set_fieldtype_arg(
           FIELDTYPE *fieldtype,
           void *(* const make_arg)(va_list *),
           void *(* const copy_arg)(const void *),
           void  (* const free_arg)(void *));
       int set_fieldtype_choice(
           FIELDTYPE *fieldtype
           bool (* const next_choice)(FIELD *, const void *),
           bool (* const prev_choice)(FIELD *, const void *));
       FIELDTYPE *link_fieldtype(FIELDTYPE *type1,
                                 FIELDTYPE *type2);

DESCRIPTION
       The function new_fieldtype creates a new field type usable
       for data validation.  You supply it  with  field_check,  a
       predicate  to check the validity of an entered data string
       whenever the user attempt to leave a field.  The (FIELD *)
       argument  is passed in so the validation predicate can see
       the field's buffer, sizes and other attributes; the second
       argument  is an argument-block structure, about which more
       below.

       You also supply new_fieldtype with char_check, a  function
       to  validate input characters as they are entered; it will
       be passed the character to be checked and a pointer to  an
       argument-block structure.

       The  function free_fieldtype frees the space allocated for
       a given validation type.

       The function set_fieldtype associates  three  storage-man-
       agement functions with a field type.  The mak_arg function
       is automatically applied to the list of arguments you give
       set_field_type  when  attaching validation to a field; its
       job is to bundle these into  an  allocated  argument-block
       object which can later be passed to validation predicated.
       The other two hook arguments should copy  and  free  argu-
       ment-block  structures.   They  will be used by the forms-
       driver code. You must supply  the  mak_arg  function,  the
       other  two  are optional, you may supply NULL for them. In
       this case it is assumed,  that  mak_arg  doesn't  allocate
       memory  but simply loads the argument into a single scalar
       value.

       The   form    driver    requests    REQ_NEXT_CHOICE    and
       REQ_PREV_CHOICE assume that the possible values of a field
       form an ordered set, and provide the forms user with a way
       to  move  through the set.  The set_fieldtype_choice func-
       tion allows forms programmers to define successor and pre-
       decessor  functions  for  the field type.  These functions
       take the field pointer and an argument-block structure  as
       arguments.

RETURN VALUE
       The pointer-valued routines return NULL on error.

       The  integer-valued  routines  return one of the following
       codes on error:

       E_OK The routine succeeded.

       E_SYSTEM_ERROR
            System error occurred (see errno).

       E_BAD_ARGUMENT
            Routine detected an incorrect or  out-of-range  argu-
            ment.

       E_CONNECTED
            The field is already connected to a form.

SEE ALSO
       curses(3X), form(3X).

NOTES
       The header file <form.h> automatically includes the header
       file <curses.h>.

       All of the (char *) arguments of  these  functions  should
       actually  be (void *).  The type has been left uncorrected
       for strict compatibility with System V.

PORTABILITY
       These routines emulate the System V forms  library.   They
       were not supported on Version 7 or BSD versions.

AUTHORS
       Juergen  Pfeifer.   Manual  pages  and  adaptation for new
       curses by Eric S. Raymond.

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