Trying to write a class inheriting from std::exception

[dmlandrum]

I'm trying to create a exception handling class for a large-ish project I'm working on which inherits from std::exception. I found this tutorial at cplusplus.com and followed its basic instructions and used its derived class as a template. Here is my Exception class as it stands right now:

#include <exception>
#include "../types.h"

namespace nuclear
{

class Exception : public std::exception
{
public:
	Exception(string_t msg)
	{
		error = msg;
	}
	
	~Exception() throw();
	
	virtual const char* what() const throw()
	{
		return error.c_str();
	}

private:
	string_t error;
};

} // !namespace nuclear

And here is the short test program to try to use it (note the commented-out part):

#include <iostream>
#include "../types.h"
#include "exception.h"

using namespace std;

int main()
{
	nuclear::Exception e("testing...");
	
	/*try
	{
		throw e;
	}
	catch (exception& e)
	{
		cout << e.what() << endl;
	}
	*/
	return 0;
}

No matter what I do, I get this error:

/tmp/ccGK1bXn.o: In function `main':
exception_test.cpp:(.text+0x1d5): undefined reference to `nuclear::Exception::~Exception()'
/tmp/ccGK1bXn.o: In function `nuclear::Exception::Exception(std::basic_string<char, std::char_traits<char>, std::allocator<char> >)':
exception_test.cpp:(.text._ZN7nuclear9ExceptionC1ESs[nuclear::Exception::Exception(std::basic_string<char, std::char_traits<char>, std::allocator<char> >)]+0x1d): undefined reference to `vtable for nuclear::Exception'
collect2: ld returned 1 exit status

What I really want is to be able to define an Exception object as it is thrown, like this:

void dostuff()
{
    // do stuff here... oops, something goes wrong!
    throw nuclear::Exception e("Error: you messed up!");
}

Is that possible? Thank you for your help!

[Duoas]

You have to define the destructor. Change line 15 to ~Exception() throw() { } Hope this helps.

[dmlandrum]

Hey, that helped immensely! Thank you!

Granted, I still have other errors to deal with, but at least they're not as cryptic...

[Duoas]

Heh heh, after a while you'll begin to understand the messages --even really long hairy ones. Then you start to wonder if you've been staring at this stuff too long... :)

[Duoas]

For whom? Me? Or dmlandrum? Please respond via PM to the person of interest.

[dmlandrum]

Yeah, it seems obvious now that I know. :)

I still can't get this to work: throw nuclear::Exception e("error"); But this works just fine: nuclear::Exception e("error"); throw e; Not quite as elegant, but it works.

[Duoas]

It is because you are using a const-string initializer but your ctor argument is not const. Use the following instead: Exception( const string& msg ) Sorry I didn't catch that earlier.

[dmlandrum]

Actually, as it turns out, this works just fine as my class is now: throw nuclear::Exception("error message"); Apparently, one can throw an object without naming it. I just tested it, and it works. The fellow I'm working with on our largish project pointed this out to me.

Thank you very much again for your help!