Invoking a function from another class with Boost in c++

Question

I am fairly new to both c++ and the boost library.

What I want to do is invoke a method foo from a class Bar inside a class Baz . Here is basically what I want to achieve:

Baz::doSomething() {
    Bar bar;

    boost::thread qux(bar.foo);
}

And the foo function could be something like:

// bar.cpp

void foo() {
    const int leet = 1337; // Very useful
}

However, when I try to compile it tells me that:

error: no matching function for call to ‘boost::thread::thread(<unresolved overloaded function type>)’
/usr/local/include/boost/thread/detail/thread.hpp:215:9: note: candidates are: boost::thread::thread(boost::detail::thread_move_t<boost::thread>)
/usr/local/include/boost/thread/detail/thread.hpp:201:18: note:                 boost::thread::thread(F, typename boost::disable_if<boost::is_convertible<T&, boost::detail::thread_move_t<T> >, boost::thread::dummy*>::type) [with F = void (Snake::*)(), typename boost::disable_if<boost::is_convertible<T&, boost::detail::thread_move_t<T> >, boost::thread::dummy*>::type = boost::thread::dummy*]
/usr/local/include/boost/thread/detail/thread.hpp:154:9: note:                 boost::thread::thread()
/usr/local/include/boost/thread/detail/thread.hpp:122:18: note:                 boost::thread::thread(boost::detail::thread_data_ptr)
/usr/local/include/boost/thread/detail/thread.hpp:113:9: note:                 boost::thread::thread(boost::thread&)

What am I missing here?

Answer 1

Member functions are different from free functions. You need to use std::mem_fun_ref to get a functor and boost::bind (or std::bind should your compiler support it) to bind the object on which the function should be called on to use them.

The end result should look something like this:

boost::thread qux(boost::bind(&Foo::bar, bar)); // makes a copy of bar
boost::thread qux(boost::bind(&Foo::bar, &bar)); // make no copy of bar and calls the original instance

Or don't use bind and let thread do the binding:

boost::thread qux(&Foo::bar, &bar);

Edit: I remembered wrong: You don't need mem_fun , boost::bind supports pointers to members out of the box.

Thanks for the comments addressing the issue.

Answer 2

boost::thread qux(boost::bind(
    &Bar::foo,      // the method to invoke
    &bar            // the instance of the class
    ));