form_field(3X)

NAME
form_fieldtype - define validation-field types

SYNOPSIS
#include <form.h>
FIELDTYPE *new_fieldtype(int (*field_check)(FIELD *, char *),
                        int (*char_check)(int, char *));
int free_fieldtype(FIELDTYPE *fieldtype);
in set_fieldtype_arg(FIELDTYPE *fieldtype
                     char *(*mak_arg)(va_list *),
                     char *(*copy_arg)(char *),
                     void (*free_arg)(char *));
in set_fieldtype_choice(FIELDTYPE *fieldtype
                        int (*next_choice)(FIELD *, char *),
                        int (*prev_choice)(FIELD *, char *));
FIELDTYPE *link_fieldtype(FIELDYPE *type1, FIELDTYPE *type2);

DESCRIPTION
The function new_fieldtype creates a new field type usable for data validation. You supply it with field_check, a predicate to check the validity of an entered data string whenever the user attempt to leave a field. Thhe (FIELD *) argument is passed in so the validation predicate can see the field's buffer, sizes and other attributes; the second argument is an argument-block structure, about which more below. You also supply new_fieldtype with char_check, a function to validate input characters as they are entered; it will be passed the character to be checked and a pointer to an argument-block structure. The function free_fieldtype frees the space allocated for a given validation type. The function set_fieldtype associates three storage-management functions with a field type. The mak_arg function is automatically applied to the list of arguments you give set_field_type when attaching validation to a field; its job is to bundle these into an allocated argument-block object which can later be passed to validation predicated. The other two hook arguments should copy and free argument-block structures. They will be used by the forms-driver code. The form driver requests REQ_NEXT_CHOICE and REQ_PREV_CHOICE assume that the possible values of a field form an ordered set, and provide the forms user with a way to move through the set. The set_fieldtype_choice function allows forms programmers to define successor and predecessor functions for the field type. These functions take the field pointer and an argument-block structure as arguments.

RETURN VALUE
The character-pointer-valued routines return NULL on error. The integer-valued routines return one of the following codes on error:

E_OK
    The routine succeeded.

E_SYSTEM_ERROR
    System error occurred (see errno).

E_BAD_ARGUMENT
    Routine detected an incorrect or out-of-range argument.

E_CONNECTED
    The field is already connected to a form.

SEE ALSO
curses(3X), form(3X).

NOTES
The header file <form.h> automatically includes the header file <curses.h>. All of the (char *) arguments of these functions should actually be (void *). The type has been left uncorrected for strict compatibility with System V.

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.