Boost Exception

namespace
boost
    {
    class
    exception
        {
        protected:
    
        exception();
        exception( exception const & x );    
        ~exception();    
        };    
    
    template <class Tag,class T>
    class error_info;    
    
    typedef error_info<struct tag_throw_function,char const *> throw_function;
    typedef error_info<struct tag_throw_file,char const *> throw_file;
    typedef error_info<struct tag_throw_line,int> throw_line;
    }