[boost] compiler bug with shared_ptr

From: Sam Partington (Sam.Partington_at_[hidden])
Date: 2002-07-05 05:40:45

Hi all,

I came across an interesting compiler bug recently with MSVC 6 SP5 and
version 1.27 of boost:

#include <boost/smart_ptr.hpp>

class A {};
typedef boost::shared_ptr<A> my_ptr;

A* f();

int main()
{
        my_ptr a;
        a = f();
        return 0;
}

The code should not compile (shared_ptr does not have an operator= which
takes a T*) and should not link ( f() is not defined anywhere).

But rather than rejecting it, the compiler happily allows it all, and simply
misses out the offending line. (see disassembly at the bottom).  If I change
the ptr type to be auto_ptr, or scoped_ptr then the compiler correctly
rejects it.

I have tested this with boost 1.28 and the compiler correctly rejects it, so
all is well.  But my company is not able at this time to move on to 1.28,
and I suspect others are in similar situations.

Whilst this is clearly a compiler bug, it is such a serious bug (and easily
brought about during migration of an app from plain pointers to
shared_ptr's) would it be possible for a warning in the documentation for
users of MSVC 6 and boost 1.27?

Apologies if this has already been discussed.

Sam

Disassembly:

10:   int main()
11:   {
00401040 55                   push        ebp
00401041 8B EC                mov         ebp,esp
00401043 83 EC 4C             sub         esp,4Ch
00401046 53                   push        ebx
00401047 56                   push        esi
00401048 57                   push        edi
00401049 8D 7D B4             lea         edi,[ebp-4Ch]
0040104C B9 13 00 00 00       mov         ecx,13h
00401051 B8 CC CC CC CC       mov         eax,0CCCCCCCCh
00401056 F3 AB                rep stos    dword ptr [edi]
12:       my_ptr a;
00401058 6A 00                push        0
0040105A 8D 4D F8             lea         ecx,[ebp-8]
0040105D E8 AD FF FF FF       call
@ILT+10(boost::shared_ptr<A>::shared_ptr<A>) (0040100f)
13:       a = f();
14:       return 0;
00401062 C7 45 F4 00 00 00 00 mov         dword ptr [ebp-0Ch],0
00401069 8D 4D F8             lea         ecx,[ebp-8]
0040106C E8 99 FF FF FF       call
@ILT+5(boost::shared_ptr<A>::~shared_ptr<A>) (0040100a)
00401071 8B 45 F4             mov         eax,dword ptr [ebp-0Ch]
15:   }