form_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 sup-
ply it with field_check, a predicate to check the validity of an entered data string when-
ever the user attempt to leave a field. The (FIELD *) argument is passed in so the vali-
dation predicate can see the field's buffer, sizes and other attributes; the second argu-
ment 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 argu-
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 form driver requests REQ_NEXT_CHOICE and REQ_PREV_CHOICE assume that the possible val-
ues 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 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.
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.
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.