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:

            •   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.

       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

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

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.