Re: Exception handling problem

From:
"Thomas J. Gritzan" <phygon_antispam@gmx.de>
Newsgroups:
comp.lang.c++
Date:
Thu, 04 Jul 2013 00:25:35 +0200
Message-ID:
<kr28d0$7td$1@newsreader4.netcologne.de>
Am 03.07.2013 23:29, schrieb woodbrian77@gmail.com:

On Wednesday, July 3, 2013 9:18:30 PM UTC, Victor Bazarov wrote:

You're supposed to catch what's thrown. I didn't see the code that
throws. Did you write it? Or does it come from the system?


       throw eof("sockRead -- rc == 0. len: ") << len; // <-- this line

Sorry. The line with the comment throws. I get the
same message/what string/ either way and I've checked
that that message is only thrown in this one place.


Throwing together a short example with the same problem:

#include <iostream>

struct failure {
     failure& self() {
         return *this;
     }
};
struct eof : failure {};

int main()
{
     try {
         throw eof().self();
     }
     catch (eof const&) {
         std::cout << "ok!" << std::endl;
     }
     catch (...) {
         std::cout << "problem!" << std::endl;
     }
}

You don't throw an /eof/, you throw a /failure/ because operator<<
returns a failure&. This is called slicing.

--
Thomas

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