Thread: Throwing an exception in int main()

I noticed that I don't have to explicitly catch an exception thrown in the main() function. I just throw it, and what was thrown is outputted to screen, and the program is automatically terminated prematurely.

Why is this?

An uncaught exception is required by the standard to result in stack unwinding (e.g. all local variables or objects are cleaned up for all call functions) and program termination.

Presumably your implementation (compiler, library, etc) also causes relevant output to occur. The standard does not require that, so such behaviour is not guaranteed with other implementations.

Originally Posted by grumpy

An uncaught exception is required by the standard to result in stack unwinding and program termination.

Yes to termination, but whether stack unwinding happens is implementation-defined. (IIRC, GCC will unwind, VC++ won't.)

Originally Posted by CornedBee

Yes to termination, but whether stack unwinding happens is implementation-defined. (IIRC, GCC will unwind, VC++ won't.)

Not true. The standard requires stack unwinding (or, more precisely, an equivalent observable effect of invoking destructors for all auto variables in sequence). If VC++ does not do that, then VC++ is not standard-compliant.

From [except.handle]p9:

If no matching handler is found, the function std::terminate() is called; whether or not the stack is unwound before this call to std::terminate() is implementation-defined (15.5.1).

I don't make claims about the standard without first looking things up.

Thanks guys. I appreciate the info.

Originally Posted by Mozza314

There is never a requirement in C++ to catch exceptions, if you don't catch it, your program terminates.

Maybe your programs do, mine crash if i don't catch a thrown exception!

Crashing is just one form of terminating.

Originally Posted by CornedBee

Crashing is just one form of terminating.

... Oh, ok. I just figured that "termination" means "user-friendly program exit".

All my main() functions look the same:

Code:

int main(int argc, char** argv) 
{
	using namespace std;
	try {
		return main_program(argc,argv);
	}
	catch (runtime_error& e) {
		cerr << RED << "Run-time error : " << e.what() << NORMAL << endl;
	}
	catch (bad_alloc&) {
		statusFailed();
		cerr << RED << "Out of memory." << NORMAL << endl;
	}
	catch (exception& e) {
		cerr << RED << "Exception : " << e.what() << NORMAL << endl;
	}
	catch (...) {
		cerr << RED << "Unknown error" << NORMAL << endl;
	}
	return 1;
}

Then main_program takes the role of the main function.