[Bug c++/31652] New: postfix increment semantics implemented incorrectly

["gcc-bugzilla at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org>]

g++ parses the code correctly and calls the correct overloaded
increment operators, but in the wrong postfix order.  The semantics of
postfix are to take the rvalue before invoking the method.  Note this
is not related to multiple reference ordering between sequence points
as the object is only referenced once.  Although I have not checked
postfix decrement, it may have the same semantic problem and it is
trivial to adapt the supplied code.

Environment:
System: Linux dbox 2.6.18-3-686 #1 SMP Sun Dec 10 19:37:06 UTC 2006 i686
GNU/Linux
Architecture: i686


host: i486-pc-linux-gnu
build: i486-pc-linux-gnu
target: i486-pc-linux-gnu
configured with: ../src/configure -v
--enable-languages=c,c++,fortran,objc,obj-c++,treelang --prefix=/usr
--enable-shared --with-system-zlib --libexecdir=/usr/lib
--without-included-gettext --enable-threads=posix --enable-nls
--program-suffix=-4.1 --enable-__cxa_atexit --enable-clocale=gnu
--enable-libstdcxx-debug --enable-mpfr --with-tune=i686
--enable-checking=release i486-linux-gnu

How-To-Repeat:
cat > a.cpp
#include <iostream>

class C
{
public:
  int v;

  C( int v ) : v( v ) {}

  C & operator++( void ) { v++;      return *this; }
  C & operator++( int )  { v += 100; return *this; }
};

main()
{
  C a( 0 );
  C b( 0 );

  std::cout << "a:" << a.v << std::endl;  // 0
  std::cout << "b:" << b.v << std::endl;  // 0

  b = ++a;

  std::cout << "a:" << a.v << std::endl;  // 1
  std::cout << "b:" << b.v << std::endl;  // 1

  b = a++;

  std::cout << "a:" << a.v << std::endl;  // 101
  std::cout << "b:" << b.v << std::endl;  // should be 1, not 101!
}
^D
> g++ a.cpp ; ./a.out
a:0
b:0
a:1
b:1
a:101
b:101


------- Comment #1 from hayward at loup dot net  2007-04-21 23:39 -------
Fix:
Execute postfix methods *after* evaluating the expression they are in.


-- 
           Summary: postfix increment semantics implemented incorrectly
           Product: gcc
           Version: 4.1.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: hayward at loup dot net
 GCC build triplet: i486-pc-linux-gnu
  GCC host triplet: i486-pc-linux-gnu
GCC target triplet: i486-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31652