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form_fieldtype

Section: Library calls (3X)
Updated: 202-0-18
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NAME

form_fieldtype - define validatio-field types

SYNOPSIS

#include <form.h>

FIELDTYPE *new_fieldtype(
    bool (* const field_check)(FIELD *, const void *),
    bool (* const char_check)(int, const void *));
int free_fieldtype(FIELDTYPE *fieldtype);

int set_fieldtype_arg(
    FIELDTYPE *fieldtype,
    void *(* const make_arg)(va_list *),
    void *(* const copy_arg)(const void *),
    void  (* const free_arg)(void *));
int set_fieldtype_choice(
    FIELDTYPE *fieldtype,
    bool (* const next_choice)(FIELD *, const void *),
    bool (* const prev_choice)(FIELD *, const void *));

FIELDTYPE *link_fieldtype(FIELDTYPE *type1,
                          FIELDTYPE *type2);

DESCRIPTION

new_fieldtype

The function new_fieldtype creates a new field type usable for data validation. Its parameters are function pointers:

field_check

This function checks the validity of an entered data string whenever the user attempts to leave a field. It has two arguments:

: .IP * 4 The (FIELD *) argument is passed in so the validation predicate can see the field's buffer, sizes and other attributes.
.IP * 4 The second argument is an argumen-block structure, about which more below.

char_check

This function validates input characters as they are entered. The form library passes it the character to be checked and a pointer to an argumen-block structure.

free_fieldtype

The free_fieldtype function frees the space allocated for a given validation type by new_fieldtype.

set_fieldtype_arg

The function set_fieldtype_arg associates three storag-management functions with a field type:

make_arg: This function is automatically applied to the list of arguments you give set_field_type when attaching validation to a field. It stores the arguments in an allocated argumen-block object which is used when validating input.
copy_arg: This function may be used by applications to copy argumen-blocks.
free_arg: Frees an argumen-block structure.

You must supply the make_arg function. The other two are optional: you may supply NULL for them. In this case, the form library assumes that make_arg does not allocate memory but simply loads the argument into a single scalar value.

set_fieldtype_choice

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 argumen-block structure as arguments.