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

Personally, I wouldn’t consider passing in a function pointer like you are trying to do as very C++ like. That’s coding C in C++

Instead, I’d wrap that thing in a class. The big advantage there is you can just override the class to have however many members you want, rather than having to perform greazy casting tricks to get at your parameters every time.

The code’s a little long-winded, so I pushed it to the end. But what it lets you do is something like this:

   class print_some : public basic_thread {     private:        int i;     public:             print_some (int i) : i(i) {};        action_callback () {           std::cout << i << std::endl;        }     }     int main () {        print_some printer (155);     } 

Here’s some exerpted example code from one of our classes that does this:

class basic_thread :  { public:    basic_thread(); protected:    unsigned long m_ThreadId;     virtual void action_callback () {};     // Internal routine used to bridge between OS callback format and     // action_callback. *Must* be static for the OS.    static unsigned long __stdcall self_calling_callback (void *parameter); } 

…and in the .cpp:

unsigned long __stdcall basic_thread::self_calling_callback (void *parameter) {    if (parameter) {       basic_thread * thread = reinterpret_cast<basic_thread *>(parameter);       thread->action_callback();    }    return 0; // The value returned only matters if someone starts calling GetExitCodeThread              // to retrieve it. }  basic_thread::basic_thread () {    // Start thread.    m_Handle = CreateThread(NULL,                            0,                            self_calling_callback,                            (PVOID)this,                            0,                            &m_ThreadId );    if( !IsHandleValid() )       throw StartException('CreateThread() failed', GetLastError());  }