Re: c++/5995: double call of copy constructor

Re: c++/5995: double call of copy constructor

[jason]

Synopsis: double call of copy constructor

State-Changed-From-To: analyzed->closed
State-Changed-By: jason
State-Changed-When: Mon Mar 18 08:58:14 2002
State-Changed-Why:
    duplicate of 4222.

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=5995

Re: c++/5995: double call of copy constructor

[jason]

Synopsis: double call of copy constructor

Responsible-Changed-From-To: unassigned->jason
Responsible-Changed-By: jason
Responsible-Changed-When: Mon Mar 18 06:27:17 2002
Responsible-Changed-Why:
    x
State-Changed-From-To: open->analyzed
State-Changed-By: jason
State-Changed-When: Mon Mar 18 06:27:17 2002
State-Changed-Why:
    yep, that's a bug.

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=5995

c++/5995: double call of copy constructor

[martin.gerbershagen]

>Number:         5995
>Category:       c++
>Synopsis:       double call of copy constructor
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          wrong-code
>Submitter-Id:   net
>Arrival-Date:   Mon Mar 18 03:16:01 PST 2002
>Closed-Date:
>Last-Modified:
>Originator:     Martin Gerbershagen
>Release:        g++-3.0.3
>Organization:
>Environment:
sparc-sun-solaris2.6
>Description:
The attached test program x.C generates the following output:

O::O()
o1(getOcopy())
O::O(const O& s)
O::O(const O& s)
O::~O()
o2(getOref())
O::O(const O& s)
&o3(getOref())
o4 = getOref()
O::O(const O& s)
&o5 = getOcopy()
O::O(const O& s)
o6 = getOcopy()
O::O(const O& s)
o7 = getOcopy()
O::O()
O::O(const O& s)
O::operator=
O::~O()
o7 = getOref()
O::operator=
(void)getOcopy()
O::O(const O& s)
O::~O()
end
O::~O()
O::~O()
O::~O()
O::~O()
O::~O()
O::~O()
O::~O()

The output shows, that the copy constructor of O is called
twice during the initialization of o1. This should not be the case and can result in performance degradation, if the class used has complex members. The test program works
properly, if it is compiled with g++ 2.95.3.
>How-To-Repeat:
g++ -O x.C && a.out
>Fix:

>Release-Note:
>Audit-Trail:
>Unformatted:
----gnatsweb-attachment----
Content-Type: text/plain; name="x.C"
Content-Disposition: inline; filename="x.C"

#include <iostream.h>

class O {
public:
   O& operator=(const O&);
   O(const O&);
   O();
   ~O();
};

O& O::operator=(const O& s)
{
   cout << "O::operator=" << endl;
   if (this != &s) {
   }
   return *this;
}

O::O(const O& s)
{
   cout << "O::O(const O& s)" << endl;
}

O::O()
{
   cout << "O::O()" << endl;
}

O::~O()
{
   cout << "O::~O()" << endl;
}

class A {
   O o;
public:
   O getOcopy() const;
   const O& getOref() const;
   A& operator=(const A&);
   A(const A&);
   A();
   ~A();
};

inline O A::getOcopy() const {
   return o;
}

inline const O& A::getOref() const {
   return o;
}

A& A::operator=(const A& s)
{
   if (this != &s) {
      o = s.o;
   }
   return *this;
}

A::A(const A& s):
   o(s.o) {
}

A::A()
{
}

A::~A()
{
}


int main() {
   A a;
   cout << "o1(getOcopy())" << endl;
   O o1(a.getOcopy());

   cout << "o2(getOref())" << endl;
   O o2(a.getOref());

   cout << "&o3(getOref())" << endl;
   const O &o3(a.getOref());

   cout << "o4 = getOref()" << endl;
   O o4 = a.getOref();

   cout << "&o5 = getOcopy()" << endl;
   const O &o5 = a.getOcopy();

   cout << "o6 = getOcopy()" << endl;
   O o6 = a.getOcopy();

   cout << "o7 = getOcopy()" << endl;
   O o7;
   o7 = a.getOcopy();

   cout << "o7 = getOref()" << endl;
   o7 = a.getOref();

   cout << "(void)getOcopy()" << endl;
   a.getOcopy();

   cout << "end" << endl;
   return 0;
}