Pointer to a function pointer

I'm trying to pass function pointers as arguments in a list of void pointers. However, ISO C forbids storing a function pointer as a void pointer, so I instead use the address of a function pointer variable, as so:

Code:

generic_func( void **args )
{
 // generic stuff
}

void callback( void ) 
{
  // specific stuff
}

int main( )
{
  void (*func)(void) = callback;
  void *args[] = { &func, ... };
  generic_func( args );
}

The problem is with the syntax for casting a void pointer back into a pointer to a function pointer. I've tried the following:

Code:

void *arg = &func;
*(unsigned __stdcall (*)(void *) *)arg...
*(unsigned __stdcall (**)(void *))arg...

The first doesn't parse correctly, the second does not dereference into the proper function pointer type. Can anyone suggest the correct syntax for this?

You can wrap function pointer in a struct and pass struct address.

Code:

typedef struct func_wrapper {
    void (*call_back)(void);
}func_wrapper;

generic_func(func_wrapper args[ ] ) 
{
    args[1].call_back();          /* call it */
}

int main(void)
{
   func_wrapper args[] = { &callback , ... };
  generic_func(args);
  return 0;
}

I used to use structs to pass args, but then you can't use generics.

I did figure out the problem, and my c-syntax was mostly correctly; however, anyone using the win32 API will be keen to know that the problem was the association of __stdcall:

Code:

*(unsigned __stdcall (**)(void *))arg... // is wrong
*(unsigned (__stdcall **)(void *))arg... // is correct

Needless to say, that was frustrating.

Of course it is wrong. There's never a place in C where this is valid: (*)

The star * indicates that you're either dereferencing a pointer, or declaring a pointer (since we're not talking about multiplication here). Pointers have to be tied to a specific type, so that you actually know what type of pointer it is actually pointing at. You don't have one, you just have some stars. So naturally it's wrong.


Quzah.