form_fieldtype(3) | Library calls | form_fieldtype(3)

# NAME

form_fieldtype - define validation-field types

# SYNOPSIS

#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);

# DESCRIPTION

## new_fieldtype

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

field_check
  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.

char_check
  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.

## free_fieldtype

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

## set_fieldtype_arg

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

make_arg
  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.
copy_arg
  This function may be used by applications to copy argument-blocks.
free_arg
  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.

## set_fieldtype_choice

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.

## link_fieldtype

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

# RETURN VALUE

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

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

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

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

# SEE ALSO

curses(3), form(3), form_field_validation(3).

# NOTES

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

# PORTABILITY

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

# AUTHORS

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

2023-07-01 | ncurses 6.4