[LLVMbugs] [Bug 17625] Precompiler Error "##"

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=17625

jonathan.sauer at gmx.de changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |jonathan.sauer at gmx.de
         Resolution|---                         |INVALID

--- Comment #1 from jonathan.sauer at gmx.de ---
I get with clang r192574 on Mac OS X:

% ~/LLVM/build/Release+Asserts/bin/clang -c clang.c clang.c:9:3: error: pasting
formed '"Hello""World"', an invalid preprocessing token
  TESTDEFINE2("Hello", "World");
  ^
clang.c:4:41: note: expanded from macro 'TESTDEFINE2'
#define TESTDEFINE2(a,b) printf("%s", a ## b) 
                                        ^
1 error generated.


I think that clang's behavior is correct, as per C11 §6.10.3.3p3 the result of
the token pasting operator ## must be a valid preprocessing token or the
behavior is undefined; and while a single string literal is a valid
preprocessing token (as defined in §6.4p3), two string literals are not (they
would be if they were *two separate* tokens, but ## produces a *single* token).

If you are coming from Visual C, this might help you:
http://stackoverflow.com/questions/1206624/differences-in-macro-concatenation-operator-between-visual-c-and-gcc

To get the code to work with clang, simply remove the "##", as string literals
next to each other will  automatically be concatenated.

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