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No match for operator "<<"

Hello,
Im trying to compile boost's variant example which is given in boost web site.

#include "boost/variant.hpp"
#include <iostream>

class my_visitor : public boost::static_visitor<int>
{
public:
    int operator()(int i) const
    {
        return i;
    }
    
    int operator()(const std::string & str) const
    {
        return str.length();
    }
};

int main()
{
    boost::variant< int, std::string > u("hello world");
    std::cout << u; // output: hello world

    int result = boost::apply_visitor( my_visitor(), u );
    std::cout << result; // output: 11 (i.e., length of "hello world")
}

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But it gives an error like this

No match for operator "<<" ... ... .... variant_io.hpp

What could be the problem?

Kind regards

HappyCactus

Here it compiles and work fine:

HappyCactus$ g++ --version
i686-apple-darwin10-g++-4.2.1 (GCC) 4.2.1 (Apple Inc. build 5659)
Copyright (C) 2007 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

anaconda:b HappyCactus$ grep BOOST_LIB_VERSION /usr/local/include/boost/version.hpp
// BOOST_LIB_VERSION must be defined to be the same as BOOST_VERSION
#define BOOST_LIB_VERSION "1_44"
anaconda:b HappyCactus$

Check carefully your compilation options and the include path. If you have multiple version of boost, remove all but the most recent. and upgrade boost.

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