Let's say I have a class such as
class c {
// ...
void *print(void *){ cout << "Hello"; }
}
And then I have a vector of c
vector<c> classes; pthread_t t1;
classes.push_back(c());
classes.push_back(c());
Now, I want to create a thread on c.print();
And the following is giving me the problem below: pthread_create(&t1, NULL, &c[0].print, NULL);
Error Ouput: cannot convert ‘void* (tree_item::)(void)’ to ‘void* ()(void)’ for argument ‘3’ to ‘int pthread_create(pthread_t*, const pthread_attr_t*, void* ()(void), void*)’
You can't do it the way you've written it because C++ class member functions have a hidden this
parameter passed in. pthread_create()
has no idea what value of this
to use, so if you try to get around the compiler by casting the method to a function pointer of the appropriate type, you'll get a segmetnation fault. You have to use a static class method (which has no this
parameter), or a plain ordinary function to bootstrap the class:
class C
{
public:
void *hello(void)
{
std::cout << "Hello, world!" << std::endl;
return 0;
}
static void *hello_helper(void *context)
{
return ((C *)context)->hello();
}
};
...
C c;
pthread_t t;
pthread_create(&t, NULL, &C::hello_helper, &c);