http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51823
Bug #: 51823
Summary: reverse iterator instantiated with POD type returns
uninitialized values + work around
Classification: Unclassified
Product: gcc
Version: 4.6.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: jakobsyb...@gmail.com
Created attachment 26299
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=26299
*.i* output of minimal example that reproduces the bug
System info:
$ uname -a
Linux ****** 3.0.0-14-generic #23-Ubuntu SMP Mon Nov 21 20:28:43 UTC 2011
x86_64 x86_64 x86_64 GNU/Linux
$ g++ -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/4.6.1/lto-wrapper
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu/Linaro
4.6.1-9ubuntu3' --with-bugurl=file:///usr/share/doc/gcc-4.6/README.Bugs
--enable-languages=c,c++,fortran,objc,obj-c++,go --prefix=/usr
--program-suffix=-4.6 --enable-shared --enable-linker-build-id
--with-system-zlib --libexecdir=/usr/lib --without-included-gettext
--enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.6
--libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu
--enable-libstdcxx-debug --enable-libstdcxx-time=yes --enable-plugin
--enable-objc-gc --disable-werror --with-arch-32=i686 --with-tune=generic
--enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu
--target=x86_64-linux-gnu
Thread model: posix
gcc version 4.6.1 (Ubuntu/Linaro 4.6.1-9ubuntu3)
Attachment:
* ostream_iterator_reverse_iterator.ii: output of:
g++ -save-temps -o ostream_iterator_reverse_iterator -Wall
ostream_iterator_reverse_iterator.cc
where ostream_iterator_reverse_iterator.cc is a minimal example that
reproduces the bug.
Headerfiles involved:
<iterator>
Compile command: g++ -o ostream_iterator_reverse_iterator -Wall
ostream_iterator_reverse_iterator.cc
Description:
Consider an iterator class that implements the requirements of a
forward_iterator. We underlying datatype is always POD and the operator*()
member of the iterator returns the results by value, since it is POD anyway.
Upon creating a reverse_iterator from this class a simple for-loop produces the
expected results:
Returning 9 9
Returning 8 8
Returning 7 7
Returning 6 6
Returning 5 5
Returning 4 4
Returning 3 3
Returning 2 2
Returning 1 1
Returning 0 0
but using the reverse_iterator in std::copy() with std::ostream_iterator
produces:
Returning 9 32767
Returning 8 32767
Returning 7 32767
Returning 6 32767
Returning 5 32767
Returning 4 32767
Returning 3 32767
Returning 2 32767
Returning 1 32767
Returning 0 32767
It seems that the internal value does not get copied. When using -O3 both the
for-loop and the copy() construct produce 0 (zero) for each call to operator*()
in the reverse_iterator, but not in the normal iterator.
The 'work-around' forces the use of forwarding. I put it as comment in the
minimum example. If I should have attached a separate source file with just the
operator*()-line replaced, I wish to express my apologies in advance.
The source file with the work-around instead of the original version of
operator*() needs an additional compiler option though: -std=c++0x
However, even with this version, the result with -O3 is still all zeros; not
what I expected, but since that is the same as before, I guess that is more
likely to be me misunderstanding what is supposed to happen with -O3 switched
on.
