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)).

SEE ALSO

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

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.

                                                                          field_validation(3FORM)