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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
   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:

            o   The (FIELD *) argument is passed in so the validation
                predicate can see the field's buffer, sizes and other
                attributes.

            o   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(3X), form(3X), form_field_validation(3X).

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.

                                                            form_fieldtype(3X)