DOKK / manpages / debian 11 / ncurses-doc / field_arg.3form.en
field_validation(3FORM) field_validation(3FORM)

form_field_validation - data type validation for fields

#include <form.h>

int set_field_type(FIELD *field, FIELDTYPE *type, ...);
FIELDTYPE *field_type(const FIELD *field);
void *field_arg(const FIELD *field);

FIELDTYPE *TYPE_ALNUM;
FIELDTYPE *TYPE_ALPHA;
FIELDTYPE *TYPE_ENUM;
FIELDTYPE *TYPE_INTEGER;
FIELDTYPE *TYPE_NUMERIC;
FIELDTYPE *TYPE_REGEXP;
FIELDTYPE *TYPE_IPV4;

The function set_field_type declares a data type for a given form field. This is the type checked by validation functions. The predefined types are as follows:

Alphanumeric data. Requires a third int argument, a minimum field width.
Character data. Requires a third int argument, a minimum field width.
Accept one of a specified set of strings. Requires additional parameters:
  • a third (char **) argument pointing to a string list;
  • a fourth int flag argument to enable case-sensitivity;
  • and 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.
Integer data, parsable to an integer by atoi(3). Requires additional parameters:
  • a third int argument controlling the precision,
  • a fourth long argument constraining minimum value,
  • and 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).
Numeric data (may have a decimal-point part). This requires additional 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).
Regular expression data. Requires a regular expression (char *) third argument. 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.
An Internet Protocol Version 4 address. This requires no additional argument. The library checks whether or not the buffer has the form a.b.c.d, where a,b,c and d are numbers between 0 and 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. See the fieldtype(3FORM) manual page.

The functions field_type and field_arg return NULL on error. The function set_field_type returns one of the following:

The routine succeeded.
System error occurred (see errno(3)).

ncurses(3NCURSES), form(3FORM), form_variables(3FORM).

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

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.