form_fieldtype(3X)														form_fieldtype(3X)

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

       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 pred-
       icate 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_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 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 pre-
       decessor functions for the field type.  These functions take the field pointer and an argument-block structure as arguments.

RETURN VALUE

       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.

       E_SYSTEM_ERROR
	    System error occurred (see errno).

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

       E_CONNECTED
	    The field is already connected to a form.

SEE ALSO

       curses(3X), form(3X).

NOTES

       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.

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.

																form_fieldtype(3X)