BUGS   [plain text]

                                   GCC Bugs

   The   latest   version   of  this  document  is  always  available  at

Table of Contents

     * [2]Reporting Bugs
          + [3]What we need
          + [4]What we DON'T want
          + [5]Where to post it
          + [6]Detailed bug reporting instructions
          + [7]Detailed bug reporting instructions for GNAT
          + [8]Detailed bug reporting instructions when using a precompiled
     * [9]Frequently Reported Bugs in GCC
          + [10]C++
               o [11]Missing features
               o [12]Bugs fixed in the 3.4 series
          + [13]Fortran
     * [14]Non-bugs
          + [15]General
          + [16]C
          + [17]C++
               o [18]Common problems when upgrading the compiler

                                Reporting Bugs

   The main purpose of a bug report is to enable us to fix the bug. The most
   important prerequisite for this is that the report must be complete and

   Before you report a bug, please check the [19]list of well-known bugs and,
   if possible, try a current development snapshot. If you want to report a bug
   with versions of GCC before 3.4 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.

Summarized bug reporting instructions

   After this summary, you'll find detailed bug reporting instructions, that
   explain how to obtain some of the information requested in this summary.

  What we need

   Please include in your bug report all of the following items, the first
   three of which can be obtained from the output of gcc -v:
     * the exact version of GCC;
     * the system type;
     * the options given when GCC was configured/built;
     * the complete command line that triggers the bug;
     * the compiler output (error messages, warnings, etc.); and
     * the preprocessed file (*.i*) that triggers the bug, generated by adding
       -save-temps to the complete compilation command, or, in the case of a
       bug report for the GNAT front end, a complete set of source files (see

  What we do not want

     * A source file that #includes header files that are left out of the bug
       report (see above)
     * That source file and a collection of header files.
     * An attached archive (tar, zip, shar, whatever) containing all (or some
       :-) of the above.
     * A code snippet that won't cause the compiler to produce the exact output
       mentioned in the bug report (e.g., a snippet with just a few lines
       around  the one that apparently triggers the bug, with some pieces
       replaced with ellipses or comments for extra obfuscation :-)
     * The  location  (URL) of the package that failed to build (we won't
       download it, anyway, since you've already given us what we need to
       duplicate the bug, haven't you? :-)
     * An error that occurs only some of the times a certain file is compiled,
       such that retrying a sufficient number of times results in a successful
       compilation; this is a symptom of a hardware problem, not of a compiler
       bug (sorry)
     * Assembly files (*.s) produced by the compiler, or any binary files, such
       as object files, executables, core files, or precompiled header files
     * Duplicate  bug  reports,  or  reports of bugs already fixed in the
       development tree, especially those that have already been reported as
       fixed last week :-)
     * Bugs in the assembler, the linker or the C library. These are separate
       projects,  with separate mailing lists and different bug reporting
     * Bugs in releases or snapshots of GCC not issued by the GNU Project.
       Report them to whoever provided you with the release
     * Questions about the correctness or the expected behavior of certain
       constructs that are not GCC extensions. Ask them in forums dedicated to
       the discussion of the programming language

  Where to post it

   Please  submit  your  bug report directly to the [20]GCC bug database.
   Alternatively, you can use the gccbug script that mails your bug report to
   the bug database.
   Only  if  all  this  is absolutely impossible, mail all information to

Detailed bug reporting instructions

   Please refer to the [22]next section when reporting bugs in GNAT, the Ada
   compiler, or to the [23]one after that when reporting bugs that appear when
   using a precompiled header.

   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

     gcc -v -save-temps all-your-options source-file

   The only excuses to not send us the preprocessed sources are (i) if you've
   found a bug in the preprocessor, (ii) if you've reduced the testcase to a
   small file that doesn't include any other file or (iii) if the bug appears
   only when using precompiled headers. 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
   .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

   Please avoid posting an archive (.tar, .shar or .zip); we generally need
   just a single file to reproduce the bug (the .i/.ii/.f 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. This is, for example, the case if you
   are using INCLUDE directives in Fortran code, which are not processed by the
   preprocessor, but the compiler. In that case, we need the main file and all
   INCLUDEd files. 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.

Detailed bug reporting instructions for GNAT

   See the [24]previous section for bug reporting instructions for GCC language
   implementations other than Ada.

   Bug reports have to contain at least the following information in order to
   be useful:
     * the exact version of GCC, as shown by "gcc -v";
     * the system type;
     * the options when GCC was configured/built;
     * the exact command line passed to the gcc program triggering the bug (not
       just the flags passed to gnatmake, but gnatmake prints the parameters it
       passed to gcc)
     * a collection of source files for reproducing the bug, preferably a
       minimal set (see below);
     * a description of the expected behavior;
     * a description of actual behavior.

   If  your  code  depends  on  additional  source files (usually package
   specifications), submit the source code for these compilation units in a
   single file that is acceptable input to gnatchop, i.e. contains no non-Ada
   text. If the compilation terminated normally, you can usually obtain a list
   of dependencies using the "gnatls -d main_unit" command, where main_unit is
   the file name of the main compilation unit (which is also passed to gcc).

   If you report a bug which causes the compiler to print a bug box, include
   that bug box in your report, and do not forget to send all the source files
   listed after the bug box along with your report.

   If you use gnatprep, be sure to send in preprocessed sources (unless you
   have to report a bug in gnatprep).

   When you have checked that your report meets these criteria, please submit
   it according to our [25]generic instructions. (If you use a mailing list for
   reporting, please include an "[Ada]" tag in the subject.)

Detailed bug reporting instructions when using a precompiled header

   If you're encountering a bug when using a precompiled header, the first
   thing to do is to delete the precompiled header, and try running the same
   GCC command again. If the bug happens again, the bug doesn't really involve
   precompiled headers, please report it without using them by following the
   instructions [26]above.

   If you've found a bug while building a precompiled header (for instance, the
   compiler crashes), follow the usual instructions [27]above.

   If you've found a real precompiled header bug, what we'll need to reproduce
   it is the sources to build the precompiled header (as a single .i file), the
   source file that uses the precompiled header, any other headers that source
   file includes, and the command lines that you used to build the precompiled
   header and to use it.

   Please don't send us the actual precompiled header. It is likely to be very
   large and we can't use it to reproduce the problem.

                        Frequently Reported Bugs in GCC

   This is a list of bugs in GCC 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.

   There are many reasons why a reported bug doesn'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 code have a simple work-around: fix the code.


  Missing features

   The export keyword is not implemented.
          Most C++ compilers (G++ included) do not yet implement export, which
          is necessary for separate compilation of template declarations and
          definitions. Without export, a template definition must be in scope
          to be used. The obvious workaround is simply to place all definitions
          in the header itself. Alternatively, the compilation unit containing
          template definitions may be included from the header.

  Bugs fixed in the 3.4 series

   The following bugs are present up to (and including) GCC 3.3.x. They have
   been fixed in 3.4.0.

   Two-stage name-lookup.
          GCC did not implement two-stage name-lookup (also see [28]below).

   Covariant return types.
          GCC did not implement non-trivial covariant returns.

   Parse errors for "simple" code.
          GCC gave parse errors for seemingly simple code, such as

struct A

struct B
  void foo();

A bar()
  B b(A(),A(1));  // Variable b, initialized with two temporaries
  B(A(2)).foo();  // B temporary, initialized with A temporary
  return (A());   // return A temporary

          Although being valid code, each of the three lines with a comment was
          rejected  by  GCC. The work-arounds for older compiler versions
          proposed below do not change the semantics of the programs at all.

          The problem in the first case was that GCC started to parse the
          declaration  of  b as a function called b returning B, taking a
          function returning A as an argument. When it encountered the 1, it
          was too late. To show the compiler that this should be really an
          expression, a comma operator with a dummy argument could be used:

B b((0,A()),A(1));

          The work-around for simpler cases like the second one was to add
          additional parentheses around the expressions that were mistaken as


          In the third case, however, additional parentheses were causing the
          problems: The compiler interpreted A() as a function (taking no
          arguments, returning A), and (A()) as a cast lacking an expression to
          be casted, hence the parse error. The work-around was to omit the

return A();

          This problem occurred in a number of variants; in throw statements,
          people also frequently put the object in parentheses.


   G77 bugs are documented in the G77 manual rather than explicitly listed
   here. Please see [29]Known Causes of Trouble with GNU Fortran in the G77


   The  following are not actually bugs, but are reported often enough to
   warrant a mention here.

   It is not always a bug in the compiler, if code which "worked" in a previous
   version, is now rejected. Earlier versions of GCC sometimes were less picky
   about standard conformance and accepted invalid source code. In addition,
   programming languages themselves change, rendering code invalid that used to
   be conforming (this holds especially for C++). In either case, you should
   update your code to match recent language standards.


   Problems with floating point numbers - the [30]most often reported non-bug.
          In  a  number  of  cases, GCC appears to perform floating point
          computations incorrectly. For example, the C++ program

#include <iostream>

int main()
  double a = 0.5;
  double b = 0.01;
  std::cout << (int)(a / b) << std::endl;
  return 0;

          might print 50 on some systems and optimization levels, and 49 on

          This is the result of rounding: The computer cannot represent all
          real numbers exactly, so it has to use approximations. When computing
          with  approximation, the computer needs to round to the nearest
          representable number.

          This is not a bug in the compiler, but an inherent limitation of the
          floating  point  types.  Please  study  [31]this paper for more


   Increment/decrement operator (++/--) not working as expected - a [32]problem
          with many variations.
          The following expressions have unpredictable results:

i*(++i)                 /* special case with foo=="operator*" */
std::cout << i << ++i   /* foo(foo(std::cout,i),++i)          */

          since the i without increment can be evaluated before or after ++i.

          The  C  and C++ standards have the notion of "sequence points".
          Everything that happens between two sequence points happens in an
          unspecified order, but it has to happen after the first and before
          the second sequence point. The end of a statement and a function call
          are examples for sequence points, whereas assignments and the comma
          between function arguments are not.

          Modifying a value twice between two sequence points as shown in the
          following examples is even worse:

(++i)*(++i)               /* special case with foo=="operator*" */
std::cout << ++i << ++i   /* foo(foo(std::cout,++i),++i)        */

          This leads to undefined behavior (i.e. the compiler can do anything).

   Casting does not work as expected when optimization is turned on.
          This is often caused by a violation of aliasing rules, which are part
          of the ISO C standard. These rules say that a program is invalid if
          you try to access a variable through a pointer of an incompatible
          type. This is happening in the following example where a short is
          accessed through a pointer to integer (the code assumes 16-bit shorts
          and 32-bit ints):

#include <stdio.h>

int main()
  short a[2];


  *(int *)a = 0x22222222; /* violation of aliasing rules */

  printf("%x %x\n", a[0], a[1]);
  return 0;

          The aliasing rules were designed to allow compilers more aggressive
          optimization. Basically, a compiler can assume that all changes to
          variables happen through pointers or references to variables of a
          type compatible to the accessed variable. Dereferencing a pointer
          that violates the aliasing rules results in undefined behavior.

          In the case above, the compiler may assume that no access through an
          integer pointer can change the array a, consisting of shorts. Thus,
          printf may be called with the original values of a[0] and a[1]. What
          really happens is up to the compiler and may change with architecture
          and optimization level.

          Recent versions of GCC turn on the option -fstrict-aliasing (which
          allows alias-based optimizations) by default with -O2. And some
          architectures  then really print "1111 1111" as result. Without
          optimization the executable will generate the "expected" output "2222

          To disable optimizations based on alias-analysis for faulty legacy
          code, the option -fno-strict-aliasing can be used as a work-around.

          The option -Wstrict-aliasing (which is included in -Wall) warns about
          some  - but not all - cases of violation of aliasing rules when
          -fstrict-aliasing is active.

          To fix the code above, you can use a union instead of a cast (note
          that  this  is  a GCC extension which might not work with other

#include <stdio.h>

int main()
    short a[2];
    int i;
  } u;


  u.i = 0x22222222;

  printf("%x %x\n", u.a[0], u.a[1]);
  return 0;

          Now the result will always be "2222 2222".

          For  some  more insight into the subject, please have a look at
          [33]this article.

   Cannot use preprocessor directive in macro arguments.
          Let me guess... you used an older version of GCC to compile code that
          looks something like this:

  memcpy(dest, src,
#ifdef PLATFORM1

          and you got a whole pile of error messages:

test.c:11: warning: preprocessing directive not recognized within macro arg
test.c:11: warning: preprocessing directive not recognized within macro arg
test.c:11: warning: preprocessing directive not recognized within macro arg
test.c: In function `foo':
test.c:6: undefined or invalid # directive
test.c:8: undefined or invalid # directive
test.c:9: parse error before `24'
test.c:10: undefined or invalid # directive

          This is because your C library's <string.h> happens to define memcpy
          as a macro - which is perfectly legitimate. In recent versions of
          glibc,  for  example, printf is among those functions which are
          implemented as macros.

          Versions of GCC prior to 3.3 did not allow you to put #ifdef (or any
          other preprocessor directive) inside the arguments of a macro. The
          code therefore would not compile.

          As of GCC 3.3 this kind of construct is always accepted and the
          preprocessor will probably do what you expect, but see the manual for
          detailed semantics.

          However,  this  kind  of code is not portable. It is "undefined
          behavior" according to the C standard; that means different compilers
          may do different things with it. It is always possible to rewrite
          code which uses conditionals inside macros so that it doesn't. You
          could write the above example

#ifdef PLATFORM1
   memcpy(dest, src, 12);
   memcpy(dest, src, 24);

          This is a bit more typing, but I personally think it's better style
          in addition to being more portable.

   Cannot initialize a static variable with stdin.
          This has nothing to do with GCC, but people ask us about it a lot.
          Code like this:

#include <stdio.h>

FILE *yyin = stdin;

          will not compile with GNU libc, because stdin is not a constant. This
          was  done  deliberately,  to  make it easier to maintain binary
          compatibility  when  the  type  FILE needs to be changed. It is
          surprising for people used to traditional Unix C libraries, but it is
          permitted by the C standard.

          This construct commonly occurs in code generated by old versions of
          lex  or yacc. We suggest you try regenerating the parser with a
          current version of flex or bison, respectively. In your own code, the
          appropriate fix is to move the initialization to the beginning of

          There  is  a  common  misconception that the GCC developers are
          responsible for GNU libc. These are in fact two entirely separate
          projects; please check the [34]GNU libc web pages for details.


   Nested classes can access private members and types of the containing class.
          Defect report 45 clarifies that nested classes are members of the
          class  they are nested in, and so are granted access to private
          members of that class.

   G++ emits two copies of constructors and destructors.
          In general there are three types of constructors (and destructors).

         1. The complete object constructor/destructor.
         2. The base object constructor/destructor.
         3. The allocating constructor/deallocating destructor.

          The first two are different, when virtual base classes are involved.

   Global destructors are not run in the correct order.
          Global  destructors should be run in the reverse order of their
          constructors  completing. In most cases this is the same as the
          reverse  order  of  constructors  starting, but sometimes it is
          different, and that is important. You need to compile and link your
          programs with --use-cxa-atexit. We have not turned this switch on by
          default, as it requires a cxa aware runtime library (libc, glibc, or

   Classes in exception specifiers must be complete types.
          [15.4]/1  tells you that you cannot have an incomplete type, or
          pointer  to  incomplete  (other than cv void *) in an exception

   Exceptions don't work in multithreaded applications.
          You  need  to  rebuild g++ and libstdc++ with --enable-threads.
          Remember, C++ exceptions are not like hardware interrupts. You cannot
          throw an exception in one thread and catch it in another. You cannot
          throw an exception from a signal handler and catch it in the main

   Templates, scoping, and digraphs.
          If you have a class in the global namespace, say named X, and want to
          give it as a template argument to some other class, say std::vector,
          then std::vector<::X> fails with a parser error.

          The reason is that the standard mandates that the sequence <: is
          treated  as  if  it  were  the token [. (There are several such
          combinations of characters - they are called digraphs.) Depending on
          the version, the compiler then reports a parse error before the
          character : (the colon before X) or a missing closing bracket ].

          The simplest way to avoid this is to write std::vector< ::X>, i.e.
          place  a  space between the opening angle bracket and the scope

   Copy constructor access check while initializing a reference.
          Consider this code:

class A

  A(const A&);   // private copy ctor

A makeA(void);
void foo(const A&);

void bar(void)
  foo(A());       // error, copy ctor is not accessible
  foo(makeA());   // error, copy ctor is not accessible

  A a1;
  foo(a1);        // OK, a1 is a lvalue

          Starting with GCC 3.4.0, binding an rvalue to a const reference
          requires an accessible copy constructor. This might be surprising at
          first sight, especially since most popular compilers do not correctly
          implement this rule.

          The C++ Standard says that a temporary object should be created in
          this context and its contents filled with a copy of the object we are
          trying to bind to the reference; it also says that the temporary copy
          can be elided, but the semantic constraints (eg. accessibility) of
          the copy constructor still have to be checked.

          For further information, you can consult the following paragraphs of
          the C++ standard: [dcl.init.ref]/5, bullet 2, sub-bullet 1, and

  Common problems when upgrading the compiler

    ABI changes

   The C++ application binary interface (ABI) consists of two components: the
   first defines how the elements of classes are laid out, how functions are
   called, how function names are mangled, etc; the second part deals with the
   internals of the objects in libstdc++. Although we strive for a non-changing
   ABI, so far we have had to modify it with each major release. If you change
   your compiler to a different major release you must recompile all libraries
   that contain C++ code. If you fail to do so you risk getting linker errors
   or malfunctioning programs. Some of our Java support libraries also contain
   C++ code, so you might want to recompile all libraries to be safe. It should
   not be necessary to recompile if you have changed to a bug-fix release of
   the same version of the compiler; bug-fix releases are careful to avoid ABI
   changes. See also the [35]compatibility section of the GCC manual.

   Remark: A major release is designated by a change to the first or second
   component  of the two- or three-part version number. A minor (bug-fix)
   release is designated by a change to the third component only. Thus GCC 3.2
   and 3.3 are major releases, while 3.3.1 and 3.3.2 are bug-fix releases for
   GCC 3.3. With the 3.4 series we are introducing a new naming scheme; the
   first release of this series is 3.4.0 instead of just 3.4.

    Standard conformance

   With each release, we try to make G++ conform closer to the ISO C++ standard
   (available  at  [36]http://www.ncits.org/cplusplus.htm).  We have also
   implemented  some of the core and library defect reports (available at
   [37]http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html     &

   Non-conforming legacy code that worked with older versions of GCC may be
   rejected by more recent compilers. There is no command-line switch to ensure
   compatibility in general, because trying to parse standard-conforming and
   old-style  code  at  the  same  time  would  render  the  C++ frontend
   unmaintainable. However, some non-conforming constructs are allowed when the
   command-line option -fpermissive is used.

   Two  milestones in standard conformance are GCC 3.0 (including a major
   overhaul of the standard library) and the 3.4.0 version (with its new C++

    New in GCC 3.0

     * The  standard  library is much more conformant, and uses the std::
       namespace (which is now a real namespace, not an alias for ::).
     * The standard header files for the c library don't end with .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 <sstream> instead.
     * streambuf::seekoff  &  streambuf::seekpos are private, instead use
       streambuf::pubseekoff & streambuf::pubseekpos respectively.
     * If std::operator << (std::ostream &, long long) doesn't exist, you need
       to recompile libstdc++ with --enable-long-long.

   If you get lots of errors about things like cout not being found, you've
   most likely forgotten to tell the compiler to look in the std:: namespace.
   There are several ways to do this:
     * Say std::cout at the call. This is the most explicit way of saying what
       you mean.
     * Say using std::cout; somewhere before the call. You will need to do this
       for each function or type you wish to use from the standard library.
     * Say  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 every user of your header file
       will be affected by this decision.

    New in GCC 3.4.0

   The  new  parser  brings  a lot of improvements, especially concerning
     * The "implicit typename" extension got removed (it was already deprecated
       since GCC 3.1), so that the following code is now rejected, see [14.6]:

template <typename> struct A
    typedef int X;

template <typename T> struct B
    A<T>::X          x;  // error
    typename A<T>::X y;  // OK

B<void> b;

     * For  similar reasons, the following code now requires the template
       keyword, see [14.2]:

template <typename> struct A
    template <int> struct X {};

template <typename T> struct B
    typename A<T>::X<0>          x;  // error
    typename A<T>::template X<0> y;  // OK

B<void> b;

     * We  now  have two-stage name-lookup, so that the following code is
       rejected, see [14.6]/9:

template <typename T> int foo()
    return i;  // error

     * This also affects members of base classes, see [14.6.2]:

template <typename> struct A
    int i, j;

template <typename T> struct B : A<T>
    int foo1() { return i; }       // error
    int foo2() { return this->i; } // OK
    int foo3() { return B<T>::i; } // OK
    int foo4() { return A<T>::i; } // OK

    using A<T>::j;
    int foo5() { return j; }       // OK

   In addition to the problems listed above, the manual contains a section on
   [39]Common Misunderstandings with GNU C++.


   1. http://gcc.gnu.org/bugs.html
   2. http://gcc.gnu.org/bugs.html#report
   3. http://gcc.gnu.org/bugs.html#need
   4. http://gcc.gnu.org/bugs.html#dontwant
   5. http://gcc.gnu.org/bugs.html#where
   6. http://gcc.gnu.org/bugs.html#detailed
   7. http://gcc.gnu.org/bugs.html#gnat
   8. http://gcc.gnu.org/bugs.html#pch
   9. http://gcc.gnu.org/bugs.html#known
  10. http://gcc.gnu.org/bugs.html#cxx
  11. http://gcc.gnu.org/bugs.html#missing
  12. http://gcc.gnu.org/bugs.html#fixed34
  13. http://gcc.gnu.org/bugs.html#fortran
  14. http://gcc.gnu.org/bugs.html#nonbugs
  15. http://gcc.gnu.org/bugs.html#nonbugs_general
  16. http://gcc.gnu.org/bugs.html#nonbugs_c
  17. http://gcc.gnu.org/bugs.html#nonbugs_cxx
  18. http://gcc.gnu.org/bugs.html#upgrading
  19. http://gcc.gnu.org/bugs.html#known
  20. http://gcc.gnu.org/bugzilla/
  21. mailto:gcc-bugs@gcc.gnu.org
  22. http://gcc.gnu.org/bugs.html#gnat
  23. http://gcc.gnu.org/bugs.html#pch
  24. http://gcc.gnu.org/bugs.html#detailed
  25. http://gcc.gnu.org/bugs.html#where
  26. http://gcc.gnu.org/bugs.html#detailed
  27. http://gcc.gnu.org/bugs.html#detailed
  28. http://gcc.gnu.org/bugs.html#new34
  29. http://gcc.gnu.org/onlinedocs/gcc-3.4.6/g77/Trouble.html
  30. http://gcc.gnu.org/PR323
  31. http://www.validlab.com/goldberg/paper.ps
  32. http://gcc.gnu.org/PR11751
  33. http://mail-index.NetBSD.org/tech-kern/2003/08/11/0001.html
  34. http://www.gnu.org/software/libc/
  35. http://gcc.gnu.org/onlinedocs/gcc/Compatibility.html
  36. http://www.ncits.org/cplusplus.htm
  37. http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html
  38. http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html
  39. http://gcc.gnu.org/onlinedocs/gcc/C_002b_002b-Misunderstandings.html