#ifdef with multiple tokens, is this legal?

c++ c-preprocessor language-lawyer conditional-compilation
Jeremy Friesner picture Jeremy Friesner · Oct 11, 2013 · Viewed 7k times · Source

Today I came across some C++ code that contains an #ifdef clause like this:

#ifdef DISABLE_UNTIL OTHER_CODE_IS_READY
   foo();
#endif

Note the space between "DISABLE_UNTIL" and "OTHER_CODE_IS_READY". Essentially there are two tokens specified in the #ifdef line.

My question is, is this legal C++ code? (g++ compiles it without any errors, and it apparently just ignores the second token). And if it is legal, should the second token have any effect?

Answer

abelenky picture abelenky · Oct 11, 2013

The syntax you posted is not legal, and the intended meaning is unclear.

Depending on what you hope to accomplish, can you use || or && to combine them?
(of course if this is someone else's code, I'd just reject it as inappropriate / unusable)

#if defined(DISABLE_UNTIL) || defined(OTHER_CODE_IS_READY)
    foo();
#endif

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