[Bug c++/34180] New: Default copy constructor copies const auto_ptr members

[jeidsath at gmail dot com]

It is an error to assign or copy a const auto_ptr. g++ should refuse to compile
the following code:

bug.cpp:
#include memory
int main()
{
class A
{
const std::auto_ptrint a;
};
A a;
}

Compiled with:
g++ bug.cpp

This code compiles, incorrectly, on the following version of gcc:

Using built-in specs.
Target: i386-redhat-linux
Configured with: ../configure --prefix=/usr --mandir=/usr/share/man
--infodir=/usr/share/info --enable-shared --enable-threads=posix
--enable-checking=release --with-system-zlib --enable-__cxa_atexit
--disable-libunwind-exceptions
--enable-languages=c,c++,objc,obj-c++,java,fortran,ada --enable-java-awt=gtk
--disable-dssi --enable-plugin
--with-java-home=/usr/lib/jvm/java-1.5.0-gcj-1.5.0.0/jre
--enable-libgcj-multifile --enable-java-maintainer-mode
--with-ecj-jar=/usr/share/java/eclipse-ecj.jar --with-cpu=generic
--host=i386-redhat-linux
Thread model: posix
gcc version 4.1.2 20070502 (Red Hat 4.1.2-12)


-- 
   Summary: Default copy constructor copies const auto_ptr members
   Product: gcc
   Version: 4.1.2
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: jeidsath at gmail dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34180

[Bug c++/34180] Default copy constructor copies const auto_ptr members

[jeidsath at gmail dot com]

--- Comment #1 from jeidsath at gmail dot com  2007-11-21 22:45 ---
I apologize, a line was incorrectly cut from the copy and paste, here is the
full code that should not compile, but does:

#include memory
int main()
{
class A
{
const std::auto_ptrint a;
};
A a;
A b = a;
}


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34180

[Bug c++/34180] Default copy constructor copies const auto_ptr members

[jeidsath at gmail dot com]

--- Comment #3 from jeidsath at gmail dot com  2007-11-21 23:52 ---
(In reply to comment #2)
 I think this is the issue, nothing specific to std::auto_ptr:
 
 struct G { G() { } G(G) { } };
 
 int main()
 {
   class A
   {
 const G g;
   };
   A a;
   A b = a;
 }
 

No, copying of const values is certainly allowed:

const int i = 5;
const int i2 = i; //SHOULD compile

Your struct G can also be created and copied:

G g;
G g2 = g;

However, the same does not work with const auto_ptr, because copying
is a non-const operation for auto_ptrs:

const auto_ptrint i;
const auto_ptrint i2 = i; //ERROR

Did you mean to make the copy constructor private? In that case, G
certainly won't work in my example, const or not, and g++ catches
this.

Now, if you're trying to make a more general example, try this:

#include iostream
struct H
{
   H()
   { a=5; } ;
   H(H rhs)
   { rhs.a=10; };
   int a;
};

int main()
{
   struct B
   {
   const H h;
   };
   B b;
   B b2 = b;
   std::cout  b.h.a  \n;//ERROR prints out 10,
   //b.h has been changed despite constness
}


The copy constructor for H does not take a const reference because I
am modelling auto_ptr -- compare gcc's definition of the auto_ptr copy
constructor in memory:
 auto_ptr(auto_ptr __a) throw() : _M_ptr(__a.release()) { }

Joel Eidsath


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34180

[Bug c++/34180] Default copy constructor copies const auto_ptr members

[jeidsath at gmail dot com]

--- Comment #5 from jeidsath at gmail dot com  2007-11-22 00:24 ---
 Of course, and of course. But that has nothing to do with my reduced snippet,
 which is equivalent to our standard-conforming implementation of 
 std::auto_ptr,
 as far as I can see, and, does compile, whereas it should not - to be clear, I
 think you are therefore right, just there is nothing wrong with our
 implementation of std::auto_ptr, if anything, this is a front-end issue. By 
 the
 way, ICC rejects my reduced snippet.

My fault, I see now -- I should have noticed that your copy constructor was a
non-const function. I agree that this is a front-end issue.


-- 

jeidsath at gmail dot com changed:

   What|Removed |Added

 CC||jeidsath at gmail dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34180