Re: exceptions with null pointers

From:

Markus Schoder <a3vr6dsg-usenet@yahoo.de>

Newsgroups:

comp.lang.c++

Date:

Wed, 26 Jul 2006 01:55:47 +0200

Message-ID:

<44c6af84$0$24897$9b4e6d93@newsread4.arcor-online.net>

Peter wrote:

Denis Petronenko wrote:

Hello,
in the following code i have segmentaion fault instead of exception.
Why? What i must to do to catch exceptions in such situation? Used
compiler: gcc version 3.3.6 (Debian 1:3.3.6-13)

int main()
{
  try{
    int* p = NULL;
    *p = 4;
  }
  catch(...){
     cout << "exception" << endl;
  }
  return 0;
}

if you work exclusively on Windows using the microsoft compilers,
you will get an exception.
It is very unclear to me, why on most other systems I'm aware of this
results in a signal.

Because it is much more efficient. If processor faults can throw
exceptions the compiler has no way of limiting which parts of the
code can throw an exception. Therefore Microsoft's compilers need
to generate code to keep track of stack unwind information dynamically
which causes run time overhead.

A exception is considerable more useful than a signal.

Exceptions are of not much use for processor faults because it is
almost impossible to write code that is exception safe against those
exceptions. You will end up terminating the program anyway.

I'm not certain whether it is defined to throw an exception from a
signal handler.

This is a _bad_ idea that is almost guaranteed to fail since it would
introduce the possibility of exceptions at arbitrary machine instructions
which the optimized static unwind information cannot handle.