Hiroyuki Tanaka wrote:

> Dear Readers,
>
> I am attempting to compile so Motif code using a c++ compiler. The
> code
> is roughly based on Dan Hellers book examples for building menus.
>
> When I try to compile the code I get the following error message.
>
> Could it be explained what is wrong here. Note I only have a cxx
> complier,
> but I do not want to write code that will not work with standard c as
> well. Sorry poor english.
>
> I am using Open VMS 6.2 and cxx compiler.
>
> Thanks
>
> Tanaka.
>
> ALPHA >cxx test.c
>
> {"File", (XtCallbackProc) callback, (XtPointer) 0, NULL},
> ............^
> %CXX-E-PTRMISMATCH, In the initializer for
> Menus[0]._menu_item::callback, the
> referenced type of the pointer value "(XtCallbackProc)callback" is
> "function
> (pointer to _WidgetRec, pointer to void, pointer to void) returning
> void°G ÊxÈ<
> at line number 33 in file TEST.C
>
> #include
> #include
> #include
> #include
>
> typedef struct _menu_item
> {
> char *label;
> XtCallbackProc (*callback)();

XtCallbackProc is already typedef'ed as a function pointer. Use plain:

XtCallbackProc callback;

> XtPointer callback_data;
> struct _menu_item *subitems;
> } MenuItem;
>
>
> void Addcallback(Widget parent, MenuItem *items)
> {
> int i;
> for (i = 0; items[i].label != NULL; i++)
> {
> if (items[i].callback)
> XtAddCallback(parent, XmNactivateCallback,
> (XtCallbackProc) items[i].callback, items[i].callback_data);
> }
> }
>
> void callback (Widget w, XtPointer clientdata, XtPointer calldata)
> {
>
> }
>
> MenuItem Menus[] =
> {
> {"File", (XtCallbackProc) callback, (XtPointer) 0, NULL},
> NULL,
> };

HaND,
--
Michel Bardiaux
Peaktime Belgium S.A. Bd. du Souverain, 191 B-1160 Bruxelles
Tel : +32 2 790.29.41

> typedef struct _menu_item
> {
> char *label;
> XtCallbackProc (*callback)();
> XtPointer callback_data;
> struct _menu_item *subitems;
> } MenuItem;

You appear to be declaring callback as a pointer to a function
taking no parameters and returning an XtCallbackProc function.
Shouldn't this be:

XtCallbackProc callback;

or is it:

XtCallbackProc *callback;

Also, when you declare the callback function don't you need to
declare it as extern "C" to make sure it has C linkage rather
than C++.

Martin Kirby