CODEWITHSUNDEEP
c++multithreading
Jimm
Jimm

Reputation: 8505

error while creating a thread with a class function

In below code, at thread t(&Fred::hello) i am getting an error that the term does not evaluate to a function taking 0 arguments. What is the issue?

#include <iostream>
#include <thread>

using namespace std;

class Fred
{
public:

virtual void hello();

};

void Fred::hello()
{
cout << "hello" << endl;
}

int main()
{
thread t (&Fred::hello);
t.join();

return 0;
}

Upvotes: 0

Views: 78

Answers (1)

juanchopanza
juanchopanza

Reputation: 227390

A non-static member function of class T needs to be called on an instance of T, and takes an implicit first parameter of type T* (or const, and/or volatile T*).

So

Fred f;
f.hello()

is equivalent to 

Fred f;
Fred::hello(&f);

So when you pass a non-static member function to a thread constructor, you must pass the implicit first argument too:

Fred f;
std::thread t(&Fred::hello, &f);

Upvotes: 4

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