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$Id: form_fieldtype.3x,v 1.46 2024/03/16 15:35:01 tom Exp $
.. 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:

5 field_check This function checks the validity of an entered data string whenever the user attempts to leave a field. It has two arguments:

5 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.

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:

5 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.

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

5 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.

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:

5 E_OK The routine succeeded.

5 E_BAD_ARGUMENT Routine detected an incorrect or out-of-range argument.

5 E_SYSTEM_ERROR System error occurred, e.g., malloc failure.

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

5 E_OK The routine succeeded.

5 E_BAD_ARGUMENT Routine detected an incorrect or out-of-range argument.

5 E_CONNECTED The field is already connected to a form.

5 E_CURRENT The field is the current field.

5 E_SYSTEM_ERROR System error occurred (see errno(3)).

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. \%curses(3X), \%form(3X), \%form_field_validation(3X)