'\" t
.TH form_field 3X ""
.SH NAME
\fBform_fieldtype\fR - define validation-field types
.SH SYNOPSIS
\fB#include <form.h>\fR
.br
FIELDTYPE *new_fieldtype(
    bool (* const field_check)(FIELD *, const void *),
    bool (* const char_check)(int, const void *));
.br
int free_fieldtype(FIELDTYPE *fieldtype);
.br
int set_fieldtype_arg(
    FIELDTYPE *fieldtype,
    void *(* const make_arg)(va_list *),
    void *(* const copy_arg)(const void *),
    void  (* const free_arg)(void *));
.br
int set_fieldtype_choice(
    FIELDTYPE *fieldtype
    bool (* const next_choice)(FIELD *, const void *),
    bool (* const prev_choice)(FIELD *, const void *));
.br
FIELDTYPE *link_fieldtype(FIELDTYPE *type1, 
                          FIELDTYPE *type2);
.br 
.SH DESCRIPTION
The function \fBnew_fieldtype\fR creates a new field type usable for data
validation.  You supply it with \fIfield_check\fR, 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 \fBnew_fieldtype\fR with \fIchar_check\fR,
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 \fBfree_fieldtype\fR frees the space allocated for a given
validation type.

The function \fBset_fieldtype\fR associates three storage-management functions 
with a field type.  The \fImak_arg\fR function is automatically applied to the
list of arguments you give \fBset_field_type\fR 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 argument-block structures.  They will
be used by the forms-driver code.

The form driver requests \fBREQ_NEXT_CHOICE\fR and \fBREQ_PREV_CHOICE\fR 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 \fBset_fieldtype_choice\fR
function allows forms programmers to define successor and predecessor functions
for the field type.  These functions take the field pointer and an
argument-block structure as arguments.
.SH RETURN VALUE
The pointer-valued routines return NULL on error.

The integer-valued routines return one of the following codes on
error:
.TP 5
\fBE_OK\fR
The routine succeeded.
.TP 5
\fBE_SYSTEM_ERROR\fR
System error occurred (see \fBerrno\fR).
.TP 5
\fBE_BAD_ARGUMENT\fR
Routine detected an incorrect or out-of-range argument.
.TP 5
\fBE_CONNECTED\fR
The field is already connected to a form.
.SH SEE ALSO
\fBcurses\fR(3X), \fBform\fR(3X).
.SH NOTES
The header file \fB<form.h>\fR automatically includes the header file
\fB<curses.h>\fR.

All of the \fB(char *)\fR arguments of these functions should actually be
\fB(void *)\fR.  The type has been left uncorrected for strict compatibility
with System V.
.SH PORTABILITY
These routines emulate the System V forms library.  They were not supported on
Version 7 or BSD versions.
.SH AUTHORS
Juergen Pfeifer.  Manual pages and adaptation for new curses by Eric
S. Raymond.
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