# form_fieldtype 3x 2025-01-18 ncurses 6.5 Library calls

    form_fieldtype(3x)               Library calls              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 a 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)).

## 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.

## SEE ALSO

           curses(3x), form(3x), form_field_validation(3x)

    ncurses 6.5                       2025-01-18                form_fieldtype(3x)