different result in gcc & icc in throwing exceptions

[Milind_Kulkarni__Int]

Hi,

I have following code which gives different output for g++ and icc across all versions of the compilers in Linux*.

//////////////////////////////////////

[bash]#include 

using namespace std;

int getInt(int i) throw(int) {
	throw i;
	return i;
}

int main() {
	try {
		try {
			cout << getInt(10) << " " << getInt(20) << endl;
		}
		catch(int f) {
			cout << "int: " << f << endl;
			throw;
		}
		
	}
	catch(int i) {
		cout << "outer int: " << i << endl;
	}
	

	return 0;
}
[/bash]

/////////////////////////////////

With g++ any version:-- output is

./a.out

int: 20

outer int: 20

With icc any version, output is:--

./a.out

int: 10

outer int: 10

Is that the icc seems to work right.

What is the reason for this difference in results.

[Milind_Kulkarni__Int]

When I use:--

int getInt(int i) throw()

instead of

int getInt(int i) throw(int)

I get this following error for both g++ and icc/icpc

./a.out

terminate called after throwing an instance of 'int'

Aborted

But the throw() syntax should also work. Please correct me if wrong.

Thanks

[Judith_W_Intel]

To answer the last question the throw() specification syntax means this function should not throw anything. So terminate is called when any throw occurs, no matter what the type.

[Milind_Kulkarni__Int]

Hi Judy,

The same throw() syntax works correctly in Windows* systems for icl and Microsoft* compilers , and also the runtime output also seems to be the same for both.

Then why does throw() syntax not work in Linux*.

Thanks

[Judith_W_Intel]

It is actually working correctly on Linux andincorrectly on Windows, because the Microsoft compiler allows one to specify throw specifications but omits the standard-mandate runtime behaviorif you violate them.

Judy

[Milind_Kulkarni__Int]

Okay thanks got it. I will have to throw differently in Linux* & Windows* , applying slightly different syntax, and it will work.

My only more question that is unanswered is:--

I get different result in icc vs g++ (across all versions).

In the former, I get 10, in the latter I get 20. What can be the logic for this.
Which is the correct result.

Thanks

[Judith_W_Intel]

According to the standard the behaviour is undefined here (and if you promote the remark to warning by using the -ww981 option you'll see our compiler gives a diagnostic):

t.cpp(11): warning #981: operands are evaluated in unspecified order
printf("%d %d\n",getInt(10),getInt(20));

But I think we should try to match the behaviour of Gnu in our Linux compiler.

A possible workaround for now is to use the -rev_arg_eval option which reverse the order of evaluation of the arguments so getInt(20) is evaluated first.

Judy

[kfsone]

I interviewed for Yahoo! in 2004, and they used this as an interview question :) I thought it was defined, but the behavior is undefined because of the way arguments are passed under different environments/calling conventions :)

For instance - if the values are being passed via the stack, they may be loaded backwards, whereas if they are being passed in registers, they may be loaded in the written order.