## 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);

## DESCRIPTION

           The  function  set_field_type  declares  a data type for a
           given form field.  This is the type checked by  validation
           functions.  The 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  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). Please
                notice that the string list is  not  copied,  only  a
                reference to it is stored in the field. So you should
                avoid to 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  preci-
                sion,  a  fourth  long  argument constraining minimum
                value, and a fifth long constraining  maximum  value.
                If  the  maximum  value  is less or equal 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 preci-
                sion, a fourth double argument  constraining  minimum
                value, and a fifth double constraining maximum value.
                If your system supports locale's, the  decimal  point
                character  to  be  used  must be the one specified by
                your locale.  If the maximum value is less  or  equal
                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 expres-
                sion (char *) third argument; the data  is  valid  if
                the  regular  expression matches it.  Regular expres-
                sions  are  in  the   format   of   regcomp(3x)   and
                regexec(3x).  Please  notice that the regular expres-
                sion 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 additional 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 vali-
                dated. 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 function set_field_type returns one of the fol-
           lowing:

           E_OK The routine succeeded.

           E_SYSTEM_ERROR
                System error occurred (see errno).

## SEE ALSO

           curses(3x), form(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 supported on Version 7 or BSD versions.

## AUTHORS

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