On Fri, Oct 23, 2009 at 09:58:55PM +0800, Zhang Lin wrote: > Hello, > I have encountered an issue when building ACE with MinGW and GCC 4.4.1 > The following macro was not accepted by the preprocessor and it reported such > an error: "error: operator '==' has no left operand". > > #if !defined (ACE_HAS_NONSTATIC_OBJECT_MANAGER) > # define ACE_HAS_NONSTATIC_OBJECT_MANAGER > #elif (ACE_HAS_NONSTATIC_OBJECT_MANAGER == 0) > # undef ACE_HAS_NONSTATIC_OBJECT_MANAGER > #endif /* ACE_HAS_NONSTATIC_OBJECT_MANAGER */ > > As I think, since ACE_HAS_NONSTATIC_OBJECT_MANAGER isn't defined, the #elif > branch should not be processed.
You are wrong. The C/C++ standards actually require it to be constant-expression, ( == 0) is not a valid constant expression. See http://gcc.gnu.org/PR36320 for details. > This macro is accepted by VC7.1 and Sun Studio 12. That doesn't mean this code is not buggy. Just use #else #if ... ... #endif instead of #elif ... ... Jakub
