form_field(3X)form_field(3X)NAMEform_fieldtype - define validation-field types
bool (* const field_check)(FIELD *, const void *),
bool (* const char_check)(int, const void *));
int free_fieldtype(FIELDTYPE *fieldtype);
void *(* const make_arg)(va_list *),
void *(* const copy_arg)(const void *),
void (* const free_arg)(void *));
bool (* const next_choice)(FIELD *, const void *),
bool (* const prev_choice)(FIELD *, const void *));
FIELDTYPE *link_fieldtype(FIELDTYPE *type1,
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. 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 vali‐
The function set_fieldtype associates three storage-management func‐
tions with a field type. The mak_arg function is automatically applied
to the list of arguments you give set_field_type when attaching valida‐
tion 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 struc‐
tures. They will be used by the forms-driver code. You must supply the
mak_arg function, the other two are optional, you may supply NULL for
them. In this case it is assumed, that mak_arg doesn't 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_field‐
type_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 pointer-valued routines return NULL on error.
The integer-valued routines return one of the following codes on error:
E_OK The routine succeeded.
System error occurred (see errno).
Routine detected an incorrect or out-of-range argument.
The field is already connected to a form.
SEE ALSOcurses(3X), form(3X).
The header file <form.h> automatically includes the header file
All of the (char *) arguments of these functions should actually be
(void *). The type has been left uncorrected for strict compatibility
with System V.
These routines emulate the System V forms library. They were not sup‐
ported on Version 7 or BSD versions.
Juergen Pfeifer. Manual pages and adaptation for new curses by Eric S.