[LLVMbugs] [Bug 12997] New: #define NULL __null gets redefined to 0 in linux

bugzilla-daemon at llvm.org bugzilla-daemon at llvm.org
Thu May 31 10:06:48 PDT 2012


             Bug #: 12997
           Summary: #define NULL __null gets redefined to 0 in linux
           Product: clang
           Version: trunk
          Platform: PC
        OS/Version: Windows XP
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Headers
        AssignedTo: unassignedclangbugs at nondot.org
        ReportedBy: rodrigorivascosta at gmail.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified


I have a problem with the NULL macro in linux. Consider the following program:

    #include <sys/wait.h>
    int main()
        void *p = NULL;

If I precompile it with 'g++ -E a.cpp' I get:

    # 2 "a.cpp" 2
    int main()
        void *p = __null;

Which is the expected result. But with 'clang++ -E a.cpp':

    # 2 "a.cpp" 2
    int main()
        void *p = 0;

Which is wrong!

I've traced the problem, and the NULL macro is redefined in
'/usr/include/linux/stddef.h' in both cases, but after including that that the
system headers have the following code:

    # define __need_NULL
    # include <stddef.h>

The difference here is that the 'stddef.h' from gcc redefines the NULL again,
but the one from clang does not.


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