void foo( int x = 0)
{
   switch( x )
   {
       case 0:
           printf("case 0\n");
           break;
         case 1:
           printf("case 1\n");
           break;
        default:
           printf("default\n");
           break;
    }
}
 
int main()
{
    foo();
    foo(1);
}

class msghandler
{
public:
    void HandleMessage(WNDPROC func, UINT msg);
    LRESULT CALLBACK handle(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam);
private:
    std::vector<msg_func> msglist;
};
 
LRESULT msghandler::handle(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
    std::vector<msg_func>::iterator iter;
 
    for(iter = msglist.begin(); iter < msglist.end(); iter++)  //loop until find match
    {
        if((*iter).msg == msg)
        {
            return (*iter).function(hWnd, msg, wParam, lParam); //return user defined function's return value
        }
    }
    return DefWindowProc(hWnd, msg, wParam, lParam);  //return DefWindowProc
}
 
void msghandler::HandleMessage(WNDPROC func, UINT msg)
{
    msg_func temp;
 
    temp.function = func;
    temp.msg = msg;
 
    msglist.push_back(temp);
}