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Reporting Bugs | Managing Bugs (GNATS and the test-suite) | Frequently Reported Bugs in GCC 3.0
Our preferred way of receiving bugs is via our GNATS bug reporting system.
Before you report a bug, please check the list of well-known bugs and, if possible in any way, try a current development snapshot or CodeSourcery's Online Test Compilation. If you want to report a bug with egcs 1.x or versions of GCC before 3.0 we strongly recommend upgrading to the current release first.
Before reporting that GCC compiles your code incorrectly, please
compile it with gcc -Wall
and see whether this shows
anything wrong with your code that could be the cause instead of a bug
in GCC.
After this summary, you'll find detailed bug reporting instructions, that explain how to obtain some of the information requested in this summary.
gcc -v
)gcc-lib
in the
output of gcc -v
-save-temps
to the complete
compilation command (see below)Please submit your bug report directly to our
GNATS bug database. If this is not possible,
please mail all information to
In general, all the information we need can be obtained by
collecting the command line below, as well as its output and the
preprocessed file it generates. gcc -v -save-temps all-your-options source-file Typically the preprocessed file (extension The only excuses to not send us the preprocessed sources are
(i) if you've found a bug in the preprocessor, or (ii) if you've
reduced the testcase to a small file that doesn't include any
other file. If you can't post the preprocessed sources because
they're proprietary code, then try to create a small file that
triggers the same problem. Since we're supposed to be able to re-create the assembly output
(extension Whether to use MIME attachments or Please avoid posting an archive (.tar, .shar or .zip); we generally
need just a single file to reproduce the bug (the .i/.ii preprocessed
file), and, by storing it in an archive, you're just making our
volunteers' jobs harder. Only when your bug report requires multiple
source files to be reproduced should you use an archive. In any case,
make sure the compiler version, error message, etc, are included in
the body of your bug report as plain text, even if needlessly
duplicated as part of an archive. The gcc lists have message size limits (200 kbytes) and bug reports
over those limits will currently be bounced. If your bug is larger
than that, please post it directly in GNATS. If you fail to supply enough information for a bug report to be
reproduced, someone will probably ask you to post additional
information (or just ignore your bug report, if they're in a bad day,
so try to get it right on the first posting :-). In this case, please
post the additional information to the bug reporting mailing list, not
just to the person who requested it, unless explicitly told so. If
possible, please include in this follow-up all the information you had
supplied in the incomplete bug report (including the preprocessor
output), so that the new bug report is self-contained. This section contains information mostly intended for GCC
contributors. If you find a bug, but you are not fixing it (yet): If you fix a bug for which there is already a GNATS entry: If you find a bug, and you are fixing it right then: The following bugs are very frequently reported. Fortran bugs are documented in the G77 manual rather than explicitly
listed here. Please see "Known
Causes of Trouble with GNU Fortran" in the
G77 manual.
This is the list of bugs (and non-bugs) in g++ (aka GNU C++) that
are reported very often, but not yet fixed. While it is certainly
better to fix bugs instead of documenting them, this document might
save people the effort of writing a bug report when the bug is already
well-known. How to report bugs tells you how to
report a bug.
There are many reasons why reported bugs don't get fixed. It might
be difficult to fix, or fixing it might break compatibility. Often,
reports get a low priority when there is a simple work-around. In
particular, bugs caused by invalid C++ code have a simple work-around,
fix the code. Now that there is an agreed ISO/ANSI standard
for C++, the compiler has a definitive document to adhere to. Earlier
versions might have accepted source code that is no longer
C++. This means that code which might have `worked' in a previous
version, is now rejected. You should update your code to be C++.
You should try to use the latest stable release of the GNU C++
compiler. This is currently 3.0. Many commonly reported bugs in earlier
releases are fixed in that version.
g++ 3.0 conforms much closer to the ISO C++ standard (available at
http://www.ncits.org/cplusplus.htm).
We have also implemented some of the core and library defect reports (available at
http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/cwg_defects.html
&
http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/lwg-defects.html respectively).
Another example is the parse error for the The problem is that the compiler interprets This problem occurs in a number of variants; in At Detailed bug reporting instructions
.i
for C or
.ii
for C++) will be large, so please compress the
resulting file with one of the popular compression programs such as
bzip2, gzip, zip or compress (in
decreasing order of preference). Use maximum compression
(-9
) if available. Please include the compressed
preprocessor output in your bug report, even if the source code is
freely available elsewhere; it makes the job of our volunteer testers
much easier..s
), you usually should not include
it in the bug report, although you may want to post parts of it to
point out assembly code you consider to be wrong.uuencode
is up to
you. In any case, make sure the compiler command line, version and
error output are in plain text, so that we don't have to decode the
bug report in order to tell who should take care of it. A meaningful
subject indicating language and platform also helps.Managing Bugs (GNATS and the test-suite)
Frequently Reported Bugs in GCC 3.0
General
mbx.c
from the PINE
4.30 or IMAP2000 distribution on Sparc systems running Solaris.Fortran
C++
Common problems updating from g++ 2.95 to g++ 3.0
This means you may get lots of errors about things like
std::
namespace.
std::
is now a real namespace, not an alias for
::
.
.h
, but begin with c
(i.e.
<cstdlib>
rather than <stdlib.h>
).
The .h
names are still available, but are deprecated.
<strstream>
is deprecated, use
<stringstream>
instead.
streambuf::seekoff
&
streambuf::seekpos
are private, instead use
streambuf::pubseekoff
&
streambuf::pubseekpos
respectively.
std::operator << (std::ostream &, long long)
doesn't exist, you need to recompile libstdc++ with
--enable-long-long
.
strcmp
not being found. You've most likely forgotton to
tell the compiler to look in the std::
namespace. There are
several ways to do this,
std::strcmp
at the call. This is the most explicit
way of saying what you mean.
using std::strcmp;
somewhere before the call. You
will need to do this for each function or type you wish to use from the
standard library.
using namespace std;
somewhere before the call.
This is the quick-but-dirty fix. This brings the whole of the
std::
namespace into scope. Never do this in a
header file, as you will be forcing users of your header file to do the
same.
Non-bugs
Here are some features that have been reported as bugs, but are not.
) in an
exception specification.
The first two are different, when virtual base classes are involved.
In some cases we can do better, and this is logged in GNATS.
--use-cxa-atexit
. We have not turned this
switch on by default, as it requires a cxa
aware runtime
library (libc
, glibc
, or equivalent).
Missing features
We know some things are missing from g++.
export
is not implemented.
Parse errors for "simple" code
Up to and including GCC 3.0, the compiler will give "parse error" for
seemingly simple code, such as
struct A{
A();
A(int);
void func();
};
struct B{
B(A);
B(A,A);
void func();
};
void foo(){
B b(A(),A(1)); //Variable b, initialized with two temporaries
B(A(2)).func(); //B temporary, initialized with A temporary
}
The problem is that GCC starts to parse the declaration of
b
as a function b
returning B
,
taking a function returning A
as an argument. When it
sees the 1, it is too late. The work-around in these cases is to add
additional parentheses around the expressions that are mistaken as
declarations:
(B(A(2))).func();
Sometimes, even that is not enough; to show the compiler that this
should be really an expression, a comma operator with a dummy argument
can be used:
B b((0,A()),A(1));
return
statement in
struct A{};
struct B{
A a;
A f1(bool);
};
A B::f1(bool b)
{
if (b)
return (A());
return a;
}
A()
as a
function (taking no arguments, returning A
), and
(A()
) as a cast - with a missing expression, hence the
parse error. The work-around is to omit the parentheses:
if (b)
return A();
throw
statements, people also frequently put the object in parentheses. The
exact error also somewhat varies with the compiler version. The
work-arounds proposed do not change the semantics of the program at
all; they make them perhaps less readable.
Optimization at
-O3
takes a very long time-O3
, all functions are candidates for inlining. The
heuristic used has some deficiencies which show up when allowed such
freedom. This is g++ specific, as it has an earlier inliner than gcc.