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  attempts  to
       leave  a  field.   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.

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

       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.

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).

SEE ALSO

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

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.

                                                                                                fieldtype(3FORM)