Simplest way to create class that behaves like stringstream - c++

Question

I'm making a simple Error class that should be thrown using throw statement, logged or written in console. The basic idea of the usage is:
//const char* filename is function argument
if(!file_exists(filename))
throw Error(line, file, severity)<<"Invalid argument: the file does not exist: "<<filename;
I originally wanted to extend stringstream, but my searches indicate that it's impossible to extend on streams.
I'd really like to make the error class as convenient as you can see above, which means able to "eat" various types and append them to internal error message.

Answer 1

So actually it's not so hard. You can't inherit from stringstream directly - or I just didn't find out how. You'll soon drown in std template system...
template<class _Elem,
class _Traits,
class _Alloc>
// ... mom help me!
But, you can make a template:
template <class T>
Error& Error::operator<<(T const& value) {
//private std::stringstream message
message<<value;
//You can also trigger code for every call - neat, ain't it?
}
You'll be adding all values from this method to private variable within the class:
class Error
{
public:
Error(int, const char*, int);
~Error(void);
std::string file;
unsigned int line;
//Returns message.str()
std::string what();
//Calls message.operator<<()
template <class T>
Error& operator<< (T const& rhs);
private:
std::stringstream message;
};
There's still something I'm missing - how to distinguish between types supported by stringstream and others and throw error on the line of call, rather than in Error class. Also I'd like to write own handlers for unsupported types.