# form_field_validation 3x

    form_field_validation(3x)                            form_field_validation(3x)

## NAME

           form_field_validation - data type validation for fields

## SYNOPSIS

           #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;

## DESCRIPTION

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

           TYPE_ALNUM
                Alphanumeric data.  Requires a third int argument, a minimum field
                width.

           TYPE_ALPHA
                Character data.  Requires a third int argument,  a  minimum  field
                width.

           TYPE_ENUM
                Accept  one of a specified set of strings.  Requires a third (char
                **) argument pointing to a string list; a fourth int flag argument
                to enable case-sensitivity; and a fifth int flag argument specify-
                ing 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). Please notice that the string list  is
                copied. 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).  Requires 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's man-page.

           TYPE_NUMERIC
                Numeric data (may have a decimal-point part). Requires a third int
                argument controlling the precision, a fourth double argument  con-
                straining  minimum  value, and a fifth double constraining maximum
                value. If your system supports locales, the decimal point  charac-
                ter  to  be used 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 preci-
                sion handling see printf's man-page.

           TYPE_REGEXP
                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.  Please notice that 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. This requires no addi-
                tional argument. It is checked 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. Please note that 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
           form_fieldtype(3x) manual page.

## RETURN VALUE

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

           E_OK The routine succeeded.

           E_SYSTEM_ERROR
                System error occurred (see errno).

## SEE ALSO

           curses(3x), form(3x), form_variables(3x).

## NOTES

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

## PORTABILITY

           These  routines emulate the System V forms library.  They were not sup-
           ported on Version 7 or BSD versions.

## AUTHORS

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

                                                         form_field_validation(3x)