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  fieldtype(3FORM)  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:

       •   a third int argument, a minimum field width.

   TYPE_ALPHA
       Character data.  Required parameter:

       •   a third int argument, a minimum field width.

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

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

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

       •   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:

       •   a third int argument controlling the precision,

       •   a fourth long argument constraining minimum value,

       •   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:

       •   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).

   TYPE_REGEXP
       Regular expression data.  Required parameter:

       •   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:

       •   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)).

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.

SEE ALSO

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