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NAME | SYNOPSIS | DESCRIPTION | FIELD TYPES | RETURN VALUE | PORTABILITY | AUTHORS | SEE ALSO | COLOPHON |
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form_field_validation(3X) Library calls form_field_validation(3X)
form_field_validation - data type validation for fields
#include <form.h>
void *field_arg(const FIELD *field);
FIELDTYPE *field_type(const FIELD *field);
int set_field_type(FIELD *field, FIELDTYPE *type, ...);
/* field types */
FIELDTYPE *TYPE_ALNUM;
FIELDTYPE *TYPE_ALPHA;
FIELDTYPE *TYPE_ENUM;
FIELDTYPE *TYPE_INTEGER;
FIELDTYPE *TYPE_NUMERIC;
FIELDTYPE *TYPE_REGEXP;
FIELDTYPE *TYPE_IPV4;
By default, no validation is done on form fields. You can
associate a form with a field type, making the form library
validate input.
field_arg
Returns a pointer to the field's argument block. The argument
block is an opaque structure containing a copy of the arguments
provided in a set_field_type call.
field_type
Returns a pointer to the field type associated with the form
field, i.e., by calling set_field_type.
set_field_type
The function set_field_type associates a field type with a given
form field. This is the type checked by validation functions.
Most field types are configurable, via arguments which the caller
provides when calling set_field_type.
The form library defines several field types. They are
implemented via the FIELDTYPE data structure, which contains
several pointers to functions.
See the form_fieldtype(3X) manual page, which describes functions
which can be used to construct a field-type dynamically.
The predefined types are as follows:
TYPE_ALNUM
Alphanumeric data. Required parameter:
• a third int argument, a minimum field width.
TYPE_ALPHA
Character data. Required parameter:
• a third int argument, a minimum field width.
TYPE_ENUM
Accept one of a specified set of strings. Required parameters:
• a third (char **) argument pointing to a string list;
• a fourth int flag argument to enable case-sensitivity;
• a fifth int flag argument specifying whether a partial match
must be a unique one. If this flag is off, a prefix matches
the first of any set of more than one list elements with that
prefix.
The library copies the string list, so you may use a list that
lives in automatic variables on the stack.
TYPE_INTEGER
Integer data, parsable to an integer by atoi(3). Required
parameters:
• a third int argument controlling the precision,
• a fourth long argument constraining minimum value,
• a fifth long constraining maximum value. If the maximum value
is less than or equal to the minimum value, the range is
simply ignored.
On return, the field buffer is formatted according to the printf
format specification “.*ld”, where the “*” is replaced by the
precision argument.
For details of the precision handling see printf(3).
TYPE_NUMERIC
Numeric data (may have a decimal-point part). Required
parameters:
• a third int argument controlling the precision,
• a fourth double argument constraining minimum value,
• and a fifth double constraining maximum value. If your system
supports locales, the decimal point character must be the one
specified by your locale. If the maximum value is less than
or equal to the minimum value, the range is simply ignored.
On return, the field buffer is formatted according to the printf
format specification “.*f”, where the “*” is replaced by the
precision argument.
For details of the precision handling see printf(3).
TYPE_REGEXP
Regular expression data. Required parameter:
• a third argument, a regular expression (char *) string. The
data is valid if the regular expression matches it.
Regular expressions are in the format of regcomp and regexec.
The regular expression must match the whole field. If you have
for example, an eight character wide field, a regular expression
"^[0-9]*$" always means that you have to fill all eight positions
with digits. If you want to allow fewer digits, you may use for
example "^[0-9]* *$" which is good for trailing spaces (up to an
empty field), or "^ *[0-9]* *$" which is good for leading and
trailing spaces around the digits.
TYPE_IPV4
An Internet Protocol Version 4 address. Required parameter:
• none
The form library checks whether or not the buffer has the form
a.b.c.d, where a, b, c, and d are numbers in the range 0 to 255.
Trailing blanks in the buffer are ignored. The address itself is
not validated.
This is an ncurses extension; this field type may not be available
in other curses implementations.
It is possible to set up new programmer-defined field types.
The functions field_type and field_arg return NULL on error. The
function set_field_type returns one of the following:
E_OK The routine succeeded.
E_SYSTEM_ERROR
System error occurred (see errno(3)).
These routines emulate the System V forms library. They were not
supported on Version 7 or BSD versions.
Juergen Pfeifer. Manual pages and adaptation for new curses by
Eric S. Raymond.
curses(3X), form(3X), form_fieldtype(3X), form_variables(3X)
This page is part of the ncurses (new curses) project.
Information about the project can be found at
⟨https://invisible-island.net/ncurses/ncurses.html⟩. If you have a
bug report for this manual page, send it to bug-ncurses@gnu.org.
This page was obtained from the tarball ncurses-6.6.tar.gz fetched
from ⟨https://ftp.gnu.org/gnu/ncurses/⟩ on 2026-01-16. If you
discover any rendering problems in this HTML version of the page,
or you believe there is a better or more up-to-date source for the
page, or you have corrections or improvements to the information
in this COLOPHON (which is not part of the original manual page),
send a mail to man-pages@man7.org
ncurses @NCURSES_MAJOR@.@NCU... 2025-08-16 form_field_validation(3X)
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HTML rendering created 2026-01-16 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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