Johan Råde wrote:

I'm using Boost 1.38 and Visual Studio 2008. The following code

[includes and usings omitted]

ostream& operator<<(ostream& os, const vector<int>& v) {

[function body omitted]

}

void f() { vector<int> v; str(format("%1%") % v);

}

fails to compile with the error message

1>c:\libraries\boost\boost_1_38_0\boost\format\feed_args.hpp(100) : error C2679: binary '<<' : no operator found which takes a right-hand operand of type 'const std::vector<_Ty>' (or there is no acceptable conversion) 1> with 1> [ 1> _Ty=int 1> ]

Why? How do I fix this?

The problem is that in feed_args.hpp when operator<< is called, the compiler looks in the namespaces boost and std. The former because that's the current namespace, and std because that's the namespace of the vector argument. It finds some candidates, none of which work for vector<int> and throws the error. It never bothers to check the global namespace. I don't know if there's a recommended solution for this, but you can try specializing the operator<< in std namespace namespace std { template<> ostream & operator<<(ostream & os, const vector<int>& v) { // Your code here } } I believe that is allowed because you are fully specializing the template. You aren't allowed to overload for a general vector<T> though. For a better explanation, check out this old GotW: http://www.gotw.ca/publications/mill08.htm -- Anthony Foglia Princeton Consultants (609) 987-8787 x233