Re: c++/6340: copy constructor vs non-default constructor

Re: c++/6340: copy constructor vs non-default constructor

[nathan]

Synopsis: copy constructor vs non-default constructor

State-Changed-From-To: open->closed
State-Changed-By: nathan
State-Changed-When: Thu Apr 18 00:58:37 2002
State-Changed-Why:
    not a bug.
    	Thing2 b = a;
    is formally
    	Thing2 b(Thing2 (a));
    i.e. convert a to Thing2 then copy construct b with
    that. [8.5]/14 class copy initialization case.
    But we are allowed to elide that temporary Thing2.
    See [12.8]/15 of the std. The copy ctor must
    exist and be accessible though.

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=6340

c++/6340: copy constructor vs non-default constructor

[swhite]

>Number:         6340
>Category:       c++
>Synopsis:       copy constructor vs non-default constructor
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed Apr 17 12:16:02 PDT 2002
>Closed-Date:
>Last-Modified:
>Originator:     stephen white
>Release:        3.02
>Organization:
>Environment:
red hat linux 7.1
kernel 2.4.2-2
>Description:
the attached code generates the following error:

foo.cpp: In function `int main (int, char **)':
foo.cpp:16: `Thing2::Thing2 (const Thing2 &)' is private
foo.cpp:25: within this context

while the copy constructor is private, it should never 
be called.  in fact, if it is made public, it *is*
never called.  it seems as if g++ just wants there to be 
a public copy constructor to give it a warm fuzzy feeling.

the workaround is to use:

Thing2 b( a );
>How-To-Repeat:
g++ -lstdc++ foo.cpp
>Fix:

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

#include <iostream.h>

class Thing1
{
};

class Thing2
{
public: 

   Thing2( const Thing1& r ) {
      cout << "constructing Thing2 from const Thing1&\n";
   }

private:
   Thing2( const Thing2& r ) {
      cout << "copy constructor (PROHIBITED)\n";
   }
};

int
main(int argc, char **argv)
{
   Thing1 a;
   Thing2 b = a;
}