Use OR among with #ifdef

Question

I suppose you can add code which will get executed only if 2 terms are simultaneously declared this way:

#ifdef X
#ifdef Y

//code to execute

#endif
#endif

I wonder if there's a way to execute the code if at least X or Y is declared (also consider xor), something like:

#ifdef X or #ifdef Y

// code

#endif

?

You can ignore parenthesis if you wants: `#if defined X || defined Y` , don't forget endif — Grijesh Chauhan, Jul 16 '13 at 11:19

score 18 · Accepted Answer · answered Jul 16 '13 at 11:17

18

Using defined:

#if defined(X) || defined(Y)

answered Jul 16 '13 at 11:17

Eli Iser

2

So I observed I can even use ^ for an exclusive or. – kaspersky Jul 16 '13 at 11:22
Interesting, didn't know that, thanks for the find. – Eli Iser Jul 16 '13 at 11:23
@gg.kaspersky That's probably because `defined(X)` will expand to an integer 1 or 0, so technically any operator that works with integer types will work here. You can even do `#if defined(X) + defined(Y)` to get an "or" effect. – Rapptz Jul 16 '13 at 11:26

score 3 · Answer 2 · answered Jul 16 '13 at 11:17

3

You can use operator|| like this:

#if defined(X) || defined(Y)

answered Jul 16 '13 at 11:17

Rapptz

score 1 · Answer 3 · answered Jul 16 '13 at 11:17

1

You can do this with:

#if defined(X) || defined(Y)
...
#endif

answered Jul 16 '13 at 11:17

Mats Petersson

score 0 · Answer 4 · answered Jul 16 '13 at 11:18

0

You need to say:

#if defined(X) || defined(Y)

The following 2 forms are equivalent:

#ifdef identifier
#if defined identifier

answered Jul 16 '13 at 11:18

devnull

4 Answers4