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form_fieldtype (3X) | C library functions | Unix Manual Pages | :man


form_fieldtype - define validation-field types


Return Value
See Also


#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. 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 validation type.

The function set_fieldtype associates three storage-management functions with a field type. The mak_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 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_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.


curses(3), form(3).


All of the (char *) arguments of these functions should actually be (void *). The type has been left uncorrected for strict compatibility



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