Error invalid use of non static member function thread

I have error: invalid use of non-static member function when I try to compile following code:

int main()
{
    data d;
    cta ce;
    pthread_t thread1;
    pthread_t thread2;
    pthread_create( &thread1, NULL, d.subscribe, NULL ); 
    pthread_create( &thread2, NULL, ce.startStrategy, NULL ); 
    pthread_join(thread1,NULL);
    pthread_join(thread2,NULL);

    return 0;
}

// cta.cpp
// ...
static void* cta::startStrategy()
{
    std::cout<<"haha"<<std::endl;
}

// data.cpp
// ...
static void* data::subscribe()
{ 
  std::cout<<"haha"<<std::endl;
}

getting error:

main.cpp:38:52: error: invalid use of non-static member function
pthread_create( &thread1, NULL, d.subscribe, NULL ); 
                                                ^
main.cpp:39:60: error: invalid use of non-static member function
pthread_create( &thread2, NULL, ce.startStrategy, NULL ); 

however, a similar code snippet works pretty well:

#include <iostream>
#include <pthread.h>
  class Foo {
    public:
      static void func() {
        std::cout << "hi" << std::endl;
      }
  };

  int main() {
    Foo ins;
    pthread_t pt;
    pthread_t pt1;
    pthread_create( &pt, NULL, ins.func, NULL );
    pthread_create( &pt1, NULL, ins.func, NULL );
    pthread_join(pt, NULL);
    pthread_join(pt1, NULL);
    return 0;
  }

it compile fine and prints «hi» twice, i wonder what could be wrong with my code, since I already changed from void to static void and follow the same pattern, why am I still getting non-static error?

int main()
{
data d;
cta ce;
pthread_t thread1;
pthread_t thread2;
pthread_create( &thread1, NULL, d.subscribe, NULL );
pthread_create( &thread2, NULL, ce.startStrategy, NULL );
pthread_join(thread1,NULL);
pthread_join(thread2,NULL);

return 0;
}

// cta.cpp
// ...
static void* cta::startStrategy()
{
std::cout<<"haha"<<std::endl;
}

// data.cpp
// ...
static void* data::subscribe()
{
std::cout<<"haha"<<std::endl;
}

main.cpp:38:52: error: invalid use of non-static member function
pthread_create( &thread1, NULL, d.subscribe, NULL );
^
main.cpp:39:60: error: invalid use of non-static member function
pthread_create( &thread2, NULL, ce.startStrategy, NULL );

#include <iostream>
#include <pthread.h>
class Foo {
public:
static void func() {
std::cout << "hi" << std::endl;
}
};

int main() {
Foo ins;
pthread_t pt;
pthread_t pt1;
pthread_create( &pt, NULL, ins.func, NULL );
pthread_create( &pt1, NULL, ins.func, NULL );
pthread_join(pt, NULL);
pthread_join(pt1, NULL);
return 0;
}

Решение

std::thread t1(&data::subscribe, &d);
std::thread t2(&cta::start_strategy, &ce);

Другие решения

I initially thought the problem to be the usage of std::reference_wrapper. But the compilation error is actually due to the class member function needing to be a pointer. The following compiles with gcc 7.3.1:

#include <thread>
#include <utility>
#include <functional>

class x {
public:

    void start_thread();
};

int main()
{
    x y;

    std::thread thr{&x::start_thread, std::ref(y)};
}

The usual approach to launching a thread for a class member is to pass a plain pointer as the class instance. This works too, in this case:

std::thread thr{&x::start_thread, &y};

And this is the more common syntax. The reference wrapper is not really needed. But in all cases the first parameter must be a pointer to a class method. &x::start_thread is such a pointer. x::start_thread itself isn’t. That’s the real problem.

The parameter to std::thread‘s constructor is specified merely as…

f — Callable object to execute in the new thread

You have to really dig into the definition of a callable object. The basic usage that I had in mind corresponds to the third option listed there for a callable object. But a reference wrapper is also acceptable. However, in all cases you have to have a pointer to a member function as the first argument.

Hello,
I am trying to call a function call_from_thread_description from another function inside a class and I am getting the following error. I can’t find the right to add a function to the pool.

Error: /home/hani/workspace/transform/Transform.cpp:127:104: error: invalid use of non-static member functiondr esults.push_back(thread_pool.push(Transform::call_from_thread_description, data[i], data[j], res));

void Transform::call_from_thread_description(const vector<string> & e1, const <string> & e2, <string>  & res)
{ 
//DO SOMETHING HERE
}

void Transform::computer_intersection()
{
    vector<string> res;
    int Num_Threads =  thread::hardware_concurrency();
    ctpl::thread_pool thread_pool(Num_Threads);
    for(int i = 0; i < data.size();i++)
    {
        data_sets tmp;
        for(int j = 0; j < data.size();j++)
        {
            results.push_back(thread_pool.push(call_from_thread_description, data[i], data[j], res));
            if(j % Num_Threads == 0 || j == data.size() -1)
            {
               results.clear();
            }
       }
  }
}