Re: How to determine where an exception is thrown?

From:

Ulrich Eckhardt <eckhardt@satorlaser.com>

Newsgroups:

microsoft.public.vc.language

Date:

Tue, 02 Jun 2009 10:20:39 +0200

Message-ID:

<nv3ff6-eg6.ln1@satorlaser.homedns.org>

Fred wrote:

[...] I'm wondering how to determine where an exception is thrown.
It's difficult to judge the throw point when lots of statement may
throw same exception. For example:

try
{
    vector<int> vec_foo;
    vec_foo.puch_back( 1 );
    vec_foo.puch_back( 2 );
    std::cout << vec_foo.at(3); // pos1
    ......
    std::cout << vec_foo.at(4); // pos2
}

catch( std::exception& e )
{
    ... // log error
}

When check the log, it's possible to find something like "Exception in
file: main.cpp, Line:73, Function:main, message : invalid vector<T>
subscript", but how to determine whether the exception is thrown in
pos1 or pos2?

You can't. It could even be the pos0 or pos-1, i.e. the push_back's, or
maybe even the constructor. Further, neither line will ever throw an
exception, as there is no throw statement. Rather, it will be inside
vector<int>::at(), or a subroutine thereof, where the exception is thrown,
i.e. the same position in both cases.

That said, you could create a log entry before and after each call you
expect to trigger an exception. That way you would see where the exception
came from. A very simple (a.k.a. hacking) way would be this:

  unsigned step = 0;
  try {
     foo();
     ++step;
     bar();
     ++step;
     baz();
     ++step;
  } catch(...) {
     std::cout << "exception after step #" << step << std::endl;
     throw;
  }

Uli

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