form_fieldtype(3X)                                          form_fieldtype(3X)

       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.  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 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 vali-
       dation 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 predi-
       cated.  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

       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_field-
       type_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 pointer-valued routines return NULL on error.

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

       E_OK The routine succeeded.

            System error occurred (see errno).

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

            The field is already connected to a form.

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

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

       All of the (char *) arguments of these  functions  should  actually  be
       (void  *).  The type has been left uncorrected for strict compatibility
       with System V.

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

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