'\" t
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.\" $Id: form_fieldtype.3x,v 1.28 2020/12/12 17:11:21 tom Exp $
.de bP
.ie n  .IP \(bu 4
.el    .IP \(bu 2
..
.TH form_fieldtype 3X ""
.SH NAME
\fBform_fieldtype\fR \- define validation-field types
.SH SYNOPSIS
\fB#include <form.h>\fR
.sp
\fBFIELDTYPE *new_fieldtype(\fP
    \fBbool (* const \fP\fIfield_check\fP\fB)(FIELD *, const void *),\fP
    \fBbool (* const \fP\fIchar_check\fP\fB)(int, const void *));\fP
.br
\fBint free_fieldtype(FIELDTYPE *\fP\fIfieldtype\fP\fB);\fP
.sp
\fBint set_fieldtype_arg(\fP
    \fBFIELDTYPE *\fP\fIfieldtype\fP\fB,\fP
    \fBvoid *(* const \fP\fImake_arg\fP\fB)(va_list *),\fP
    \fBvoid *(* const \fP\fIcopy_arg\fP\fB)(const void *),\fP
    \fBvoid  (* const \fP\fIfree_arg\fP\fB)(void *));\fP
.br
\fBint set_fieldtype_choice(\fP
    \fBFIELDTYPE *\fP\fIfieldtype\fP\fB,\fP
    \fBbool (* const \fP\fInext_choice\fP\fB)(FIELD *, const void *),\fP
    \fBbool (* const \fP\fIprev_choice\fP\fB)(FIELD *, const void *));\fP
.sp
\fBFIELDTYPE *link_fieldtype(FIELDTYPE *\fP\fItype1\fP\fB,\fP
                          \fBFIELDTYPE *\fP\fItype2\fP\fB);\fP
.SH DESCRIPTION
.SS new_fieldtype
The function \fBnew_fieldtype\fR creates a new field type usable for data
validation.
Its parameters are function pointers:
.TP 5
\fIfield_check\fR
This function checks the
validity of an entered data string whenever the user attempts to leave a field.
It has two arguments:
.RS
.bP
The (FIELD *) argument is passed in so the validation predicate can see the
field's buffer, sizes and other attributes.
.bP
The second argument is an
argument-block structure, about which more below.
.RE
.TP 5
\fIchar_check\fR
This function validates input characters as they are entered.
The form library passes it the character to be checked
and a pointer to an argument-block structure.
.SS free_fieldtype
.PP
The \fBfree_fieldtype\fR function
frees the space allocated for a given validation type by \fBnew_fieldtype\fP.
.SS set_fieldtype_arg
.PP
The function \fBset_fieldtype_arg\fR associates
three storage-management functions with a field type:
.TP 5
\fImake_arg\fR
This function is automatically applied to the
list of arguments you give \fBset_field_type\fR when attaching validation
to a field.
It stores the arguments in an allocated argument-block
object which is used when validating input.
.TP 5
\fIcopy_arg\fR
This function may be used by applications to copy argument-blocks.
.TP 5
\fIfree_arg\fR
Frees an argument-block structure.
.PP
You must supply the \fImake_arg\fR function.
The other two are optional: you may supply NULL for them.
In this case, the form library assumes
that \fImake_arg\fR does not allocate memory but simply loads the
argument into a single scalar value.
.SS set_fieldtype_choice
.PP
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.
.PP
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.
.SS link_fieldtype
.PP
The function \fBlink_fieldtype\fR creates
a new field type from the two given types.
They are connected by an logical 'OR'.
.SH RETURN VALUE
The pointer-valued routines return NULL on error.
They set \fBerrno\fP according to their success:
.TP 5
.B E_OK
The routine succeeded.
.TP 5
.B E_BAD_ARGUMENT
Routine detected an incorrect or out-of-range argument.
.TP 5
.B E_SYSTEM_ERROR
System error occurred, e.g., malloc failure.
.PP
The integer-valued routines return one of the following codes on
error:
.TP 5
.B E_OK
The routine succeeded.
.TP 5
.B E_BAD_ARGUMENT
Routine detected an incorrect or out-of-range argument.
.TP 5
.B E_CONNECTED
The field is already connected to a form.
.TP 5
.B E_CURRENT
The field is the current field.
.TP 5
.B E_SYSTEM_ERROR
System error occurred (see \fBerrno\fR(3)).
.SH SEE ALSO
\fBcurses\fR(3X),
\fBform\fR(3X),
\fBform_field_validation\fR(3X).
.SH NOTES
The header file \fB<form.h>\fR automatically includes the header file
\fB<curses.h>\fR.
.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.