Invalid use of non-static member function c++ thread linux

Question

I tried run a function, which starts thread, but i recived error :

error: invalid use of non-static member function ‘void Sniffer::f1(int)’

code:

#include "library.hpp"

class Sniffer
{
    void f1( int x );
    void f2();
};

void Sniffer::f1( int x )
{
    while (true)
    {
        sleep(x);
        std::cout << 1 << std::endl;
    }
}

void Sniffer::f2()
{
    int y = 5;
    std::thread t1( f1, y );
    t1.join();
}

int main()
{
    return 0;
}

Any other way, to fix it without change a function, on static function?

Answer 1

In C++ member functions have an implicit first parameter that binds to this . When creating a thread, the this pointer must be passed. You must also qualify the member function with a class name. The correct thread constructor in your case would look like this:

std::thread t1( &Sniffer::f1, this, y );

Alternatively, you could pass a lambda to the thread constructor instead:

std::thread t1([this, y] // capture the this pointer and y by value
{
    this->f1(y);
});

Answer 2

When you create std::thread it doesn't capture the this pointer for you. You would have to include the this pointer when creating the thread, or you could use a lambda that captures this or captures everything by reference.

eg:

void Sniffer::f2()
{
    int y = 5;
    std::thread t1(&Sniffer::f1, this, y);
    t1.join();
}

or:

void Sniffer::f2()
{
    int y = 5;
    std::thread t1([&,y](){f1(y); });   // captures everything (including this) by reference, captures a copy of y
                                        // becuase y coud go out of scope and be destroyed while the thread could 
                                        // continue running (even though in this case that won't happen because the join is in the same scope
    t1.join();
}

Of course, if you capture this then you don't need to mention it in the body of the lambda and without parameters needed we can remove the () which simplifies to:

void Sniffer::f2()
{
    int y = 5;
    std::thread t1([this,y]{f1(y); }); 
    t1.join();
}