pthread_create错误：

Question

i have written this piece of code for my own purpose.it will create a thread which runs a routine named event_handler().the routine event_handler will take an instance of the class object QApplication as an argument and invoke its exec() method.

#include <pthread.h>


void event_handler(void * &obj)
{
    QApplication* app = reinterpret_cast<QApplication*>(&obj);
    app.exec();
}

int main(int argc, char **argv)
{
    pthread_t p1;

    QApplication a(argc, argv);

    pthread_create(&p1, NULL, &event_handler,(void *) &a);

    //do some computation which will be performed by main thread

    pthread_join(*p1,NULL);


}

But whenever i am trying to build this piece of code, i am getting this error

main.cpp:10: error: request for member ‘exec’ in ‘app’, which is of non-class type ‘QApplication*’
main.cpp:34: error: invalid conversion from ‘void (*)(void*&)’ to ‘void* (*)(void*)’
main.cpp:34: error: initializing argument 3 of ‘int pthread_create(pthread_t*, const pthread_attr_t*, void* (*)(void*), void*)’

what is the problem in my code.(keeping in mind that i am a newbie in this area it may be a very silly mistake :-) )

Answer 1

The thread function have to take a void pointer as its argument, not a reference to an object. You can later typecast this to the correct pointer type:

void event_handler(void* pointer)
{
    QApplication* app = reinterpret_cast<QApplication*>(pointer);

    app->exec();
}

You also pass the thread identifier wrong to pthread_join . You should not use the dereferencing operator there.

---

I also recommend you look into the new C++11 threading functionality . With std::thread you can simply do:

int main()
{
    QApplication app;
    std::thread app_thread([&app]() { app.exec(); });

    // Other code

    app_thread.join();
}