C++ Thread in member function

Question

can I use thread in member function to call a member function for C++ in windows? If yes, how to implement it? Here is the sample

void Class::fun_1(void){
 _beginthread(fun_2, 0, NULL); //This is the error line :: function call missing argument list; use '&Class::fun_2' to create a pointer to member
}

void Class::fun_2(void){
 printf("hello");
}

Thanks

Answer 1

There are actually multiple issues here:

1. You can't pass a pointer to a member function as the routine to the _beginthread() function. The function requires a pointer to a global or static function.
2. Standard C++ requires that you fully qualify the member function name (even within the class) and use an & to obtain a pointer to the member (the compiler was complaining to you about this point).

Because you can't pass a member function pointer to _beginthread() , you need to create a wrapper global or static function to make it work. Here's one way to make that happen:

class MyClass
{
public:
    void fun_1()
    {  
        _beginthread(&MyClass::fun_2_wrapper, 0, static_cast<void*>(this));
    }

private:
    void fun_2()
    {
        printf("hello");  
    }  

    static void __cdecl fun_2_wrapper(void* o)
    {
        static_cast<MyClass*>(o)->fun_2();
    }
};

Of course, you need to somehow guarantee that the MyClass object will still exist for as long as fun_2() is running, or not-so-good things will happen. If you much rather not have to worry about it, consider using Boost.Thread which does basically this and much more for you.

Answer 2

The usual way to do this is to use a static member function that calls the member function using a void pointer to the original object.

class Class
{
public:
   void fun_1(void)
   {
      _beginthread( &Class::static_fun_2, 0, this );
   }
   void fun_2(void)
   {
      printf("hello");
   }
private:
   static void static_fun_2( void * args )
   {
      static_cast<Class*>(args)->fun_2();
   }

};

However if you start needing to pass arguments to those functions things get a little more complicated. I'd look at using boost::thread and boost::bind instead of rolling your own.