boost::bind and class member function

Question

Consider following example.

#include <iostream>
#include <algorithm>
#include <vector>

#include <boost/bind.hpp>

void
func(int e, int x) {
    std::cerr << "x is " << x << std::endl;
    std::cerr << "e is " << e << std::endl;
}

struct foo {
    std::vector<int> v;

    void calc(int x) {
        std::for_each(v.begin(), v.end(),
            boost::bind(func, _1, x));
    }

    void func2(int e, int x) {
        std::cerr << "x is " << x << std::endl;
        std::cerr << "e is " << e << std::endl;
    }

};

int
main()
{
    foo f;

    f.v.push_back(1);
    f.v.push_back(2);
    f.v.push_back(3);
    f.v.push_back(4);

    f.calc(1);

    return 0;
}

All works fine if I use func() function. But in real life application I have to use class member function, ie foo::func2() in this example. How can I do this with boost::bind ?

Answer 1

You were really, really close:

void calc(int x) {
    std::for_each(v.begin(), v.end(),
        boost::bind(&foo::func2, this, _1, x));
}

EDIT: oops, so was I. heh.

Although, on reflection, there is nothing really wrong with your first working example. You should really favour free functions over member functions where possible - you can see the increased simplicity in your version.

Answer 2

While using boost::bind for binding class member functions, the second argument must supply the object context. So your code will work when the second argument is this