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fieldtype(3FORM) fieldtype(3FORM)


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)).


ncurses(3NCURSES), form(3FORM), field_validation(3FORM).


The header file <form.h> automatically includes the header file <curses.h>.


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.