declaring function pointer types for callbacks

Hi all,

I am implementing some events (callbacks), and have come across a problem that I daresay has a simple solution.

The problem is that one of the inputs into my callback function is a struct that I declare later on, and it doesn't like it because the struct doesn't exist yet. The problem is that I can't move the declaration of the struct above the declaration of the callback function either, because the struct itself contains one of these callbacks!!

example:

Code:

---

typedef void (*eGPD_onButtonPress)( tGPD_widget, unsigned short, unsigned short, char, char);
typedef void (*eGPD_onMouseIn)( tGPD_widget );
typedef void (*eGPD_onMouseOut)( tGPD_widget );

typedef struct tGPD_widget{
        char type;
        void *object;
        unsigned short x;
        unsigned short y;
        tGPD_list *children;
        struct tGPD_widget *parent;
        char redraw;
        eGPD_onMouseIn onMouseIn;
        eGPD_onMouseOut onMouseOut;
}tGPD_widget;

---

As you can see, tGPD_widget contains two events/callbacks (so far) which also have tGPD_widgets as inputs.

How do I properly define these?

EDIT: If I remove the references to tGPD_widget from the callback definitions, it compiles and runs ok - however i do want the tGPD_widget input in there!

Use a forward declaration and pass a pointer to struct tGPD_widget to the callbacks.

Code:

---

struct tGPD_widget; /* forware decl. */

typedef void (*eGPD_onButtonPress)( struct tGPD_widget*, unsigned short, unsigned short, char, char);
typedef void (*eGPD_onMouseIn)( struct tGPD_widget* );
typedef void (*eGPD_onMouseOut)( struct tGPD_widget* );

typedef struct tGPD_widget{
    char type;
    void *object;
    unsigned short x;
    unsigned short y;
    tGPD_list *children;
    struct tGPD_widget *parent;
    char redraw;
    eGPD_onMouseIn onMouseIn;
    eGPD_onMouseOut onMouseOut;
}tGPD_widget;

---

gg

Thanks for the quick reply.

Firstly, sorry - tGPD_widget* (pointer to tGPD_widget) is what I originally intended to be passed in, not the struct itself.

Secondly, it compiles now (by adding the 'struct' keyword) but gives me HEAPS of warnings like this:

Code:

---

gpd_windows.h:18: warning: "struct tGPD_widget" declared inside parameter list
gpd_windows.h:18: warning: its scope is only this definition or declaration, which is probably not what you want

---

Is there any way to do this without the warnings?

I did it like this:

Code:

---

typedef struct tGPD_widget* pGPD_widget;
typedef void (*eGPD_onButtonPress)( pGPD_widget, unsigned short, unsigned short, char, char);
typedef void (*eGPD_onMouseIn)( pGPD_widget );
typedef void (*eGPD_onMouseOut)( pGPD_widget );

---

And it compiles ok. Is this 'normal' syntax?

There's nothing wrong with what I posted...

Let's see gpd_windows.h - atleast up to the tGPD_widget struct declaration (which, I'm assuming, includes line 18).

gg

>> And it compiles ok. Is this 'normal' syntax?
It isn't any different from what I posted except you typedef'd "struct tGPD_widget*" to "pGPD_widget" and used the typedef instead.

gg

Correct, but it got rid of my compiler warnings.

Thanks for your help!