error: call of overloaded ‘bind(int (Class::*)(int, int), Class*, int, int)’ is ambiguous

Question

I'm trying to use boost::bind, could anybody tell me where is wrong in the following code segment?

#include <iostream>
#include <boost/bind.hpp>

using std::cout;
using std::endl;

class Class {
public:

    int add(int x, int y) {
        cout << "x+y=" <<x+y<<endl;
        return x+y;
    }
};

int main()
{
    cout << "boost::thread: " << endl;
    Class cls;

    boost::bind<int>(&Class::add, &cls, 1, 2);

    return 0;
}

in my compiler g++-4.7, it says:

main.cpp: In function ‘int main()’:
main.cpp:26:45: error: call of overloaded ‘bind(int (Class::*)(int, int), Class*, int, int)’ is ambiguous
     boost::bind<int>(&Class::add, &cls, 1, 2);
                                             ^
main.cpp:26:45: note: candidates are:
In file included from /usr/include/boost/bind.hpp:22:0,
                 from main.cpp:3:
/usr/include/boost/bind/bind.hpp:1610:5: note: boost::_bi::bind_t<R, F, typename boost::_bi::list_av_3<A1, A2, A3>::type> boost::bind(F, A1, A2, A3) [with R = int; F = int (Class::*)(int, int); A1 = Class*; A2 = int; A3 = int; typename boost::_bi::list_av_3<A1, A2, A3>::type = boost::_bi::list3<boost::_bi::value<Class*>, boost::_bi::value<int>, boost::_bi::value<int> >]
     BOOST_BIND(F f, A1 a1, A2 a2, A3 a3)
     ^
/usr/include/boost/bind/bind_mf_cc.hpp:109:5: note: boost::_bi::bind_t<R, boost::_mfi::mf2<R, T, A1, A2>, typename boost::_bi::list_av_3<A1, A2, A3>::type> boost::bind(R (T::*)(B1, B2), A1, A2, A3) [with R = int; T = Class; B1 = int; B2 = int; A1 = Class*; A2 = int; A3 = int; typename boost::_bi::list_av_3<A1, A2, A3>::type = boost::_bi::list3<boost::_bi::value<Class*>, boost::_bi::value<int>, boost::_bi::value<int> >]
     BOOST_BIND(R (BOOST_BIND_MF_CC T::*f) (B1, B2), A1 a1, A2 a2, A3 a3)
     ^
/usr/include/boost/bind/bind_mf_cc.hpp:131:5: note: boost::_bi::bind_t<Rt2, boost::_mfi::mf2<R, T, B1, B2>, typename boost::_bi::list_av_3<A1, A2, A3>::type> boost::bind(R (T::*)(B1, B2), A1, A2, A3) [with Rt2 = int; R = int; T = Class; B1 = int; B2 = int; A1 = Class*; A2 = int; A3 = int; typename boost::_bi::list_av_3<A1, A2, A3>::type = boost::_bi::list3<boost::_bi::value<Class*>, boost::_bi::value<int>, boost::_bi::value<int> >]
     BOOST_BIND(R (BOOST_BIND_MF_CC T::*f) (B1, B2), A1 a1, A2 a2, A3 a3)

I know that's a overload issue, but the header files are included automatically, how should I do next?

Answer 1

Simple, change this line:

boost::bind<int>(&Class::add, &cls, 1, 2);

to

boost::bind(&Class::add, &cls, 1, 2)();

bind returns a function, and you need to invoke it with operator().

By the way, you do not need boost::bind in C++11. Include <functional> and use std::bind.