Re: Assertion vs Exception Handling

From:

"Leigh Johnston" <leigh@i42.co.uk>

Newsgroups:

comp.lang.c++

Date:

Tue, 16 Mar 2010 22:53:15 -0000

Message-ID:

<X9OdncYryLNFlj3WnZ2dnUVZ7vmdnZ2d@giganews.com>

"James Kanze" <james.kanze@gmail.com> wrote in message
news:2863180e-4a7f-403c-a46e-949fd311457c@b30g2000yqd.googlegroups.com...

On Mar 16, 10:13 pm, "Leigh Johnston" <le...@i42.co.uk> wrote:

"James Kanze" <james.ka...@gmail.com> wrote in message

[...]

To be taken seriously please post a VC++ testcase which
illustrates this problem (dtor not being called with
optimizations turned on) and post a defect report on Microsoft
Connect if you have not already.

http://connect.microsoft.com/VisualStudio/feedback/details/336316/missing-destructor-calls-when-optimization-is-enabled

I'm not the first to have encountered it.

I always compile with optimizations turned on and have not
suffered from this with VC9 at least.

It depends somewhat on your coding style. I'd never have
encountered in my own code, either, because I rigorously use
SESE. But the code in which I encountered it is perfectly legal
C (and arguably a case where not using SESE is valid).

My example code was:
----- CompilerError.cpp -----
#include <iostream>
#include <stdlib.h>

class Tracker
{
public:
   static int instance_count ;
#define TRACK(f) std::cout << "Tracker::" #f << "(), this = " << this
<< std::endl;
   Tracker() { TRACK(ctor); ++ instance_count ;}
   Tracker(Tracker const& ) { TRACK(copy); ++ instance_count ;}
   ~Tracker() { TRACK(dtor); -- instance_count; }
   Tracker const& operator=(Tracker const& ) { TRACK(asgn); return
*this; }
#undef TRACK

};

int Tracker::instance_count = 0;

Tracker f()
{
   for ( int i = 0; i < 2; ++ i )
   {
           std::cout << i << ": start" << std::endl;
           Tracker t;
           if ( i != 0 )
           {
                   std::cout << i << ": returning" << std::endl;
                   return t;
           }
           std::cout << i << ": end" << std::endl;
   }
   std::cerr << "I don't believe it" << std::endl;
   abort();

}

void g()
{
   Tracker t(f());
   std::cout << "After f()" << std::endl;

}

int
main()
{
   g();
   std::cout << Tracker::instance_count << " remaining Trackers" <<
std::endl;
   return 0;
}
----- CompilerError.cpp -----

(Copy pasted from my original posting in
microsoft.public.vc.language. I hope the neither Windows nor
Google introduce any anomalies.)

--
James Kanze

Yeah thanks I found it on Microsoft Connect through a search. The following
is a workaround to the problem:

struct foo
{
    foo() { std::cout << "ctor\n"; }
    ~foo() { std::cout << "dtor\n"; }
};

typedef std::tr1::shared_ptr<foo> MyType;

MyType f(int max_tries)
{
    if (true)
        while (max_tries > 0) {
            MyType p( new foo );
            // The following is actually some fairly
            // complicated calculations...
            --max_tries;
            if (max_tries < 2)
                return p;
        }
    else
        return MyType();
    throw std::runtime_error( "didn't work" );
}

It is very lame of Microsoft that this bug was reported in early 2008 and is
still not fixed.

/Leigh