# 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 additional
                parameters:

                o   a third (char **) argument pointing to a string list;

                o   a fourth int flag argument to enable case-sensitivity;

                o   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.

           TYPE_INTEGER
                Integer data, parsable to an integer by atoi(3).   Requires  addi-
                tional parameters:

                o   a third int argument controlling the precision,

                o   a fourth long argument constraining minimum value,

                o   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).  This requires addi-
                tional parameters:

                o   a third int argument controlling the precision,

                o   a fourth double argument constraining minimum value,

                o   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'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.

                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.  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
           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)