# 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>

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

           /* predefined field types */
           FIELDTYPE *TYPE_ALNUM;
           FIELDTYPE *TYPE_ALPHA;
           FIELDTYPE *TYPE_ENUM;
           FIELDTYPE *TYPE_INTEGER;
           FIELDTYPE *TYPE_NUMERIC;
           FIELDTYPE *TYPE_REGEXP;
           FIELDTYPE *TYPE_IPV4;

## DESCRIPTION

           By  default, no validation is done on form fields.  You can associate a
           form with 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.

           Several field types are predefined by the form library.

### Predefined types

           It is possible to set up new  programmer-defined  field  types.   Field
           types  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:

                o   a third int argument, a minimum field width.

           TYPE_ALPHA
                Character data.  Required parameter:

                o   a third int argument, a minimum field width.

           TYPE_ENUM
                Accept one of a specified set of strings.  Required parameters:

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

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

                o   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:

                o   a third int argument controlling the precision,

                o   a fourth long argument constraining minimum value,

                o   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:

                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(3).

           TYPE_REGEXP
                Regular expression data.  Required parameter:

                o   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:

                o   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.

## RETURN VALUE

           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)).

## SEE ALSO

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

## AUTHORS

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

                                                         form_field_validation(3x)