Bug#151065: marked as done (g++: destructor called twice)
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and subject line Not a bug: Re: Bug#151065: g++: destructor called twice
has caused the attached Bug report to be marked as done.
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Received: (at submit) by bugs.debian.org; 26 Jun 2002 13:06:47 +0000
>From peter@luft.iwr.uni-heidelberg.de Wed Jun 26 08:06:47 2002
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From: Peter Bastian <peter@luft.iwr.uni-heidelberg.de>
To: Debian Bug Tracking System <submit@bugs.debian.org>
Subject: g++: destructor called twice
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Date: Wed, 26 Jun 2002 15:06:30 +0200
Message-Id: <E17NCVC-00020q-00@luft.iwr.uni-heidelberg.de>
Delivered-To: submit@bugs.debian.org
Package: g++
Version: 2:2.95.4-14
Severity: normal
Hi !
We have problems with a C++ program reported in detail below.
It is not a Debian specific problem. In particular we checked:
- there is the same problem using GNU C++ compiler on SuSE Linux
and MacOS X
- Code compiles and executes properly on MacOS using the
CodeWarrior compiler
- Problem does not go away with g++ version 3.0
The code below compiles but when the expression
z = 3.0*x in the main function is executed the destructur of some
temporary object is called twice, leading to a segmentation
fault.
In addition there is a second problem: When the line
z = 3.0*x in main() is changed to z = x*3.0 the compiler
tries to instantiate the function template
T_leaftype operator* (double alpha, T_leaftype x) with
T_leaftype=double, but it should use the method operator*(double)
of class ScalarVector which is inherited from Vector<ScalarVector>
The code compiles and executes properly with the
CodeWarrior compiler on MacOS.
Thanks for considering this problem
------------------------>---<-----------------------------
#include<iostream>
#include<string>
using namespace std;
// The base class
template <class T_leaftype>
class Vector {
public:
T_leaftype operator* (double alpha);
protected:
Vector () {}
private:
T_leaftype& asLeaf ()
{ return static_cast<T_leaftype&>(*this);}
} ;
template <class T_leaftype>
inline T_leaftype Vector<T_leaftype>::operator* (double alpha)
{
T_leaftype z(asLeaf());
return z;
}
template <class T_leaftype>
inline T_leaftype operator* (double alpha, T_leaftype x)
{
return x.operator*(alpha);
}
// The derived class
class ScalarVector : public Vector<ScalarVector> {
public:
ScalarVector (int elements);
ScalarVector (const ScalarVector&);
~ScalarVector ();
private:
int n; // number of doubles
double *v; // array of values
} ;
ScalarVector::ScalarVector (int elements)
{
n = elements;
v = new double[n];
cout << "making ScalarVector v=" << v << endl;
}
ScalarVector::ScalarVector (const ScalarVector& x)
{
n = x.n;
v = new double[n];
for (int i=0; i<n; i++) v[i] = x.v[i];
cout << "making ScalarVector v=" << v << endl;
}
ScalarVector::~ScalarVector ()
{
cout << "delete ScalarVector v=" << v << endl;
delete[] v;
}
// main program
int main ()
{
ScalarVector x(3), z(3);
z = 3.0*x;
}
-- System Information
Debian Release: 3.0
Architecture: i386
Kernel: Linux luft 2.4.18 #1 Wed Jun 12 14:53:15 CEST 2002 i686
Locale: LANG=de_DE, LC_CTYPE=de_DE
Versions of packages g++ depends on:
ii cpp 2:2.95.4-14 The GNU C preprocessor.
ii g++-2.95 1:2.95.4-7 The GNU C++ compiler.
ii gcc-2.95 1:2.95.4-7 The GNU C compiler.
---------------------------------------
Received: (at 151065-done) by bugs.debian.org; 12 Jul 2002 10:05:12 +0000
>From doko@cs.tu-berlin.de Fri Jul 12 05:05:12 2002
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Fri, 12 Jul 2002 09:37:52 +0200 (MEST)
From: Matthias Klose <doko@cs.tu-berlin.de>
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Message-ID: <15662.34640.753151.411760@gargle.gargle.HOWL>
Date: Fri, 12 Jul 2002 09:37:52 +0200
To: Philip Martin <philip@codematters.co.uk>, 151065-done@bugs.debian.org
Cc: Peter Bastian <peter@luft.iwr.uni-heidelberg.de>
Subject: Not a bug: Re: Bug#151065: g++: destructor called twice
In-Reply-To: <87k7oj3s0o.fsf@codematters.co.uk>
References: <87k7oj3s0o.fsf@codematters.co.uk>
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Delivered-To: 151065-done@bugs.debian.org
therefore closing the report.
Philip Martin writes:
> The segmentation fault is a bug in your code, not in gcc. A temporary
> is getting constructed, and you are using the compiler generated
> assignment operator, so you get two instances deallocating the same
> memory. Try adding a private operator=
>
> class ScalarVector : public Vector<ScalarVector> {
> private:
> ScalarVector& operator=(const ScalarVector&);
> };
>
> and your code will fail to compile. Provide a suitable public
> operator= and your code should work.
>
>
> I believe the other problem can be simplified to
>
> struct A {
> double operator*(double);
> };
>
> template<typename T> T operator*(double, T);
>
> int main() {
> A a;
> a * 3.0;
> }
>
> which gives the error
> z2.cc: In function `int main()':
> z2.cc:5: `T operator*(double, const T&) [with T = double]' must have an
> argument of class or enumerated type
>
> --
> Philip
>
>
> --
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