windows - Passing function Pointers in C++

Question

i want to do this simple piece of code work.

#include <iostream>
#include <windows.h>


    void printSome (int i)
    {
        std::cout << i << std::endl;
    }

    void spawnThread (void (*threadName)(int i))
    {
        CreateThread 
            (
                0,      // default security attributes
                0,          // use default stack size 
                (LPTHREAD_START_ROUTINE)threadName,  // thread function name
                (LPVOID)i,          // argument to thread function 
                0,          // use default creation flags 
                0       // returns the thread identifier 
            );  
    }

    int main ()
    {
        spawnThread(printSome(155));
    }

i am on windows, using vs. Any help will be greatly appriciated.

Answer 1

CreateThread wants 2 arguments: pointer to the function to execute as a thread, and a DWORD argument that will be given to the thread. your spawnThread() function only has 1 argument (threadName); you think it has 2 args because of the "i", but that is really part of the definition of the "threadName" type. (you could just as well leave out the "i"; that is, you don't need to name the arguments to "threadName".)

anyway, given that you NEED 2 arguments, redefine spawnThread:

   void spawnThread(void (*threadEntryPoint)(int), int argument)
   {
      CreateThread(0,0,
                   (LPTHREAD_START_ROUTINE)threadEntryPoint,
                   (LPVOID)argument,
                   0,0);
   }

notice that i did not name the int argument to the threadEntryPoint; it is sufficient to tell the compiler that the function must have a single int argument.

and call it:

   spawnThread(printSome, 155);

anyway, quick and dirty, this will do what you want.

hth.

reilly.