man form_fieldtype (3): define validation-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

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 attempts to leave a field. The (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_arg associates three storage-management functions with a field type. The make_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. You must supply the make_arg function, the other two are optional, you may supply NULL for them. In this case it is assumed that make_arg does not allocate memory but simply loads the argument into a single scalar value.

The function link_fieldtype creates a new field type from the two given types. They are connected by an logical 'OR'.

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 pointer-valued routines return NULL on error. They set errno according to their success:

E_OK: The routine succeeded.
E_BAD_ARGUMENT: Routine detected an incorrect or out-of-range argument.
E_SYSTEM_ERROR: System error occurred, e.g., malloc failure.

The integer-valued routines return one of the following codes on error:

E_OK: The routine succeeded.
E_BAD_ARGUMENT: Routine detected an incorrect or out-of-range argument.
E_CONNECTED: The field is already connected to a form.
E_CURRENT: The field is the current field.
E_SYSTEM_ERROR: System error occurred (see errno).

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