form_fieldtype(3X) Library calls form_fieldtype(3X)

form_fieldtype - define validation-field types

#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);

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

This function checks the validity of an entered data string whenever the user attempts to leave a field. It has two arguments:
  • 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.
This function validates input characters as they are entered. The form library passes it the character to be checked and a pointer to an argument-block structure.

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

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

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 argument-block object which is used when validating input.
This function may be used by applications to copy argument-blocks.
Frees an argument-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.

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.

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

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

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

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

The routine succeeded.
Routine detected an incorrect or out-of-range argument.
The field is already connected to a form.
The field is the current field.
System error occurred (see errno(3)).

These routines emulate the System V forms library. They were not supported on Version 7 or BSD versions.

Juergen Pfeifer. Manual pages and adaptation for new curses by Eric S. Raymond.

curses(3X), form(3X), form_field_validation(3X)

2024-03-16 ncurses 6.5