$#^!% template specialization headache!

The_Nerd · 04-26-2007, 05:24 AM

Okay, I am mad. I am only mad because I've scoured the 'net, read all the books I own, and tried a million different combinations on my code. No avail. No one on the 'net has ever done this. None of the books think you can/should. And I certainly can't figure it out through combinations. So, even though I am certain I am missing something SSOOO simple, how do I do this:

Code:

/* Include nescessary headers */
#define ERROR CErrorHandler()
#define ERR_END CErrorHandler::end

class CErrorHandler
{
	public:
		typedef int end_type;
		static end_type end;
		
		template<typename T> CErrorHandler& operator<<(const T &Val)
		{
			Message << Val;
			return (*this);
		}
		
		template<CErrorHandler::end_type> CErrorHandler& operator<<(const CErrorHandler::end_type &Val)
		{
			Message << "\n";
			cout << "Error: " << this->str();
			throw Message;
		}
		
		string str()
		{
			return Message.str();
		}
		
	private:
		stringstream Message;
};

void main()
{
    ERROR << "This is an error message" << ERR_END;
}

The above code doesn't work. As you can see, I want to make an error handler that works like a stream, and as soon as end_type type is collected in the stream, it will actually THROW the error. However, this doesn't work. I've tried everything, if I do a:

Code:

template<typename T> CErrorHandler& operator<<(const T &Val)
		{
			Message << Val;
			return (*this);
		}
		
		template<> CErrorHandler& operator<< <CErrorHandler::end_type>(const CErrorHandler::end_type &Val)
		{
			Message << "\n";
			cout << "Error: " << this->str();
			throw Message;
		}

Then g++ gives the following errors (that, as usual, are extremely descriptive... right... NOT!):

Code:

In file included from source/main.cpp:5:
include/main.h:27: error: invalid explicit specialization before '>' token
include/main.h:27: error: explicit specialization in non-namespace scope `class CErrorHandler'
include/main.h:28: error: invalid member function declaration
make: *** [source/main.o] Error 1

The_Nerd · 04-27-2007, 03:11 AM

Okay, I am a little cooler now, and I am sorry I exploded, but I still need help just as badly. Please help me if you can.

dmail · 04-27-2007, 04:39 AM

If I wanted to do something like this, then I would code it like the following

Code:

#include <iostream>
#include <sstream>
#include <stdexcept>

#define ERROR CErrorHandler()
#define ERR_END CErrorHandler::end

class CErrorHandler
{
public:
	struct end_type{};
	static end_type end;

	template<typename T> CErrorHandler& operator<<(const T &Val)
	{
		Message << Val;
		return (*this);
	}

	void operator<<(const CErrorHandler::end_type &Val)
	{
		Message << std::endl;
		std::cout << "Error: " << str();
		throw std::runtime_error(Message.str() );
	}

	std::string str()
	{
		return Message.str();
	}

private:
	std::stringstream Message;
};
CErrorHandler::end_type CErrorHandler::end;

int main()
{
	ERROR << "This is an error message" << ERR_END;
}

The_Nerd · 04-27-2007, 03:45 PM

Thank you! I didn't know that was possible... see, you learn something new everyday!

I appreciate the help. I got around my problem by just making "end" a function. Since it threw a exception, it never returned, and that means the return value didn't matter anyhow, plus the return value would never get put in the error stream.

What you posted is allot of help, thanks!