bug: stack overflow in std::auto_ptr

[Bronek Kozicki]

Hi
Please try this code. I think that it's perfectly legal. However when
compiled under MSVC71 stack overflow happens in first line of main, thus
second line is never executed.
B.

#include <iostream>
#include <memory>

using namespace std;

struct A
{
virtual ~A() {}
};

struct B : public A
{
};

auto_ptr<B> test()
{
return auto_ptr<B>(new B);
};

int main()
{
auto_ptr<A> r = test();
std::cout << "You won't see this!" << std::endl;
}

[David Lowndes]

Bronek,

Compiling your code with VC7.1 gives this warning:

warning C4717: 'std::auto_ptr< B>::operator<A > std::auto_ptr_r ef<A>' :
recursive on all control paths, function will cause runtime stack
overflow

.... which is what's happening to you in practice.

The online Comeau compiler won't compile your code, saying:

""ComeauTest.c" , line 23: error: class "std::auto_ptr< A>" has no
suitable copy constructor
auto_ptr<A> r = test();
"

Dave
--
MVP VC++ FAQ: http://www.mvps.org/vcfaq

[Bronek Kozicki]

On Thu, 22 Jan 2004 14:49:54 +0000, David Lowndes wrote:

warning C4717: 'std::auto_ptr< B>::operator<A > std::auto_ptr_r ef<A>' :
recursive on all control paths, function will cause runtime stack
overflow

... which is what's happening to you in practice.
.... and puts us in the realm of Undefined Behaviour.
""ComeauTest.c" , line 23: error: class "std::auto_ptr< A>" has no
suitable copy constructor
auto_ptr<A> r = test();

which means that code is illegal. Is it ? Anyway I'd say that
"std::auto_ ptr is flawed and has to be fixed" :((
B.

[David Lowndes]

>> ""ComeauTest.c" , line 23: error: class "std::auto_ptr< A>" has no

suitable copy constructor
auto_ptr<A> r = test();
which means that code is illegal. Is it ?

Not being intimately familiar with the standards I can't say - but the
Comeau compiler is usually right.
Anyway I'd say that
"std::auto_p tr is flawed and has to be fixed" :((

From what I've read about std::auto_ptr, it has many gotchas and can
be more trouble than its worth.

Dave
--
MVP VC++ FAQ: http://www.mvps.org/vcfaq

[Hendrik Schober]

David Lowndes <da****@mvps.or g> wrote:

Bronek,

Compiling your code with VC7.1 gives this warning:

warning C4717: 'std::auto_ptr< B>::operator<A > std::auto_ptr_r ef<A>' :
recursive on all control paths, function will cause runtime stack
overflow
Funny. From VC I get this:

test.cpp(22) : error C2664: 'std::auto_ptr< _Ty>::auto_ptr( std::auto_ptr<_ Ty> &) throw()' :
cannot convert parameter 1 from 'std::auto_ptr< _Ty>' to 'std::auto_ptr< _Ty> &'
[...]

The online Comeau compiler won't compile your code, saying:

""ComeauTest.c" , line 23: error: class "std::auto_ptr< A>" has no
suitable copy constructor
auto_ptr<A> r = test();
"

while Comeau here says this:

Comeau C/C++ 4.3.3 (Aug 10 2003 15:39:53) for _MS_WINDOWS_x86 _Beta8
Copyright 1988-2003 Comeau Computing. All rights reserved.
MODE:non-strict warnings microsoft C++

"test.cpp", line 22: warning: initial value of reference to non-const must be
an lvalue
auto_ptr<A> r = test();
^
However, if I change this line

auto_ptr<A> r = test();

into this one

auto_ptr<A> r( test() );

I get your warning with VC7.1, and

initial value of reference to non-const must be an lvalue

from Comeau.
Now, when I tried this

auto_ptr<B> r = test();
auto_ptr<A> s(r);

both Comeau and VC7.1 accept the code.
I'm not sure what to make of this, but it
seems to be a work-around.
If you want to know chapter and verse of
the standard, I'd suggest you ask in either
comp.lang.c++.m oderated or comp.std.c++. I
have decided long ago that the std doc is
far beyond my abilities to digest English.
Dave

Schobi

--
Sp******@gmx.de is never read
I'm Schobi at suespammers dot org

"Sometimes compilers are so much more reasonable than people."
Scott Meyers

[David Lowndes]

> Funny. From VC I get this:

test.cpp(22) : error C2664: 'std::auto_ptr< _Ty>::auto_ptr( std::auto_ptr<_ Ty> &) throw()' :
cannot convert parameter 1 from 'std::auto_ptr< _Ty>' to 'std::auto_ptr< _Ty> &'
Mighty odd that we've got different results :(

If I get time I'll have to check what I tried again.
I have decided long ago that the std doc is far beyond my abilities to digest English.

<

Mine too.

Dave
--
MVP VC++ FAQ: http://www.mvps.org/vcfaq

[David Lowndes]

> Funny. From VC I get this:

test.cpp(22) : error C2664: 'std::auto_ptr< _Ty>::auto_ptr( std::auto_ptr<_ Ty> &) throw()' :
cannot convert parameter 1 from 'std::auto_ptr< _Ty>' to 'std::auto_ptr< _Ty> &'

I've tried again and VC7.1 (version 13.10.3077) reports the "recursive
on all control paths, function will cause runtime stack overflow"
warning for me.

The Comeau online (version 4.3.3) error is as I originally posted too.

I wonder what we have done differently?

Dave
--
MVP VC++ FAQ: http://www.mvps.org/vcfaq

[Bronek Kozicki]

On Fri, 23 Jan 2004 22:44:32 +0000, David Lowndes wrote:

I've tried again and VC7.1 (version 13.10.3077) reports the "recursive
on all control paths, function will cause runtime stack overflow"
warning for me.

The Comeau online (version 4.3.3) error is as I originally posted too.

I wonder what we have done differently?

Maybe that question should be passed to Mr. Plauger ?
B.

[Hendrik Schober]

Bronek Kozicki <br**@rubikon.p l> wrote:

On Fri, 23 Jan 2004 22:44:32 +0000, David Lowndes wrote:
[David, haven't seen your posting, so I
don't know if you wrote anything else
which I missed.]

I've tried again and VC7.1 (version 13.10.3077) reports the "recursive
on all control paths, function will cause runtime stack overflow"
warning for me.
That's funny.
I tried it again: Copy & paste the code
from Bronek's original posting int a my
test project, compile it, and get this:

------ Build started: Project: Test, Configuration: Debug Win32 ------

Compiling...
Microsoft (R) 32-bit C/C++ Optimizing Compiler Version 13.10.3077 for 80x86
Copyright (C) Microsoft Corporation 1984-2002. All rights reserved.
cl /Od /I "..\.." /D "WIN32" /D "_DEBUG" /D "_CONSOLE" /D "_MBCS" /Gm /EHsc /RTC1 /MLd /GS /Za /Zc:wchar_t /Zc:forScope /GR
/Fo"C:\Temp\Test \Debug\Test/" /Fd"C:\Temp\Test \Debug\Test/vc70.pdb" /W4 /c /Wp64 /Zi /TP
\Develop\test.c pp
test.cpp
\Develop\test.c pp(22) : error C2664: 'std::auto_ptr< _Ty>::auto_ptr( std::auto_ptr<_ Ty> &) throw()' : cannot convert parameter 1
from 'std::auto_ptr< _Ty>' to 'std::auto_ptr< _Ty> &'
with
[
_Ty=A
]
and
[
_Ty=A
]
and
[
_Ty=A
]
A reference that is not to 'const' cannot be bound to a non-lvalue

[Damn, I hate the IDE trying to copy formatted text
to the clipboard! OE is just to stupid to deal with
it. Can I have a switch to turn this off, please?!]

My "yvals.h" file has a

#define _CPPLIB_VER 313

in it.
The Comeau online (version 4.3.3) error is as I originally posted too.
Yeah:

Comeau C/C++ 4.3.3 (Aug 6 2003 15:13:37) for ONLINE_EVALUATI ON_BETA1
Copyright 1988-2003 Comeau Computing. All rights reserved.
MODE:strict errors C++

"ComeauTest .c", line 18: error: extra ";" ignored,
In C: A function definition does not end with a semicolon
In C++: A function definition, extern "C" or namespace, does not end with a semicolon
};
^

"ComeauTest .c", line 22: error: class "std::auto_ptr< A>" has no suitable copy
constructor
auto_ptr<A> r = test();
^

2 errors detected in the compilation of "ComeauTest .c".

I wonder what we have done differently?

For Comeau I know. I was using this:

Comeau C/C++ 4.3.3 (Aug 10 2003 15:39:53) for _MS_WINDOWS_x86 _Beta8
Copyright 1988-2003 Comeau Computing. All rights reserved.
MODE:non-strict warnings microsoft C++

That's what I have on disk, and I think it's
using VC's std lib. AFAIK, Comeau Online uses
libcomo, which is a derivate of SGI's std lib.
Maybe that question should be passed to Mr. Plauger ?
This might be true for the difference between
Comeau Online and my version, which does use
Plauger's std lib. (You might want to post
your question in the STL group. Or go and ask
on comp.lang.c++.m oderated ot comp.std.c++.)
However, I am still puzzled why David gets
different results with VC.
B.

Schobi

--
Sp******@gmx.de is never read
I'm Schobi at suespammers dot org

"Sometimes compilers are so much more reasonable than people."
Scott Meyers

[David Lowndes]

> That's funny.

OK, I see what the difference is now - you have the /Za "Disable
Language Extensions" compiler options set.

If I change that setting in my test project, I get the same error as
you.

I'd tested the code by creating a Win32 console application and
pasting the code it.

Dave
--
MVP VC++ FAQ: http://www.mvps.org/vcfaq