In C++, is this:
#ifdef COND_A && COND_B
the same as:
#if defined(COND_A) && defined(COND_B)
?
I was thinking it wasn't, but I haven't been able to find a difference with my compiler (VS2005).
views:
499answers:
3
+8
A:
They are not the same. The first one doesn't work (I tested in gcc 4.4.1). Error message was:
test.cc:1:15: warning: extra tokens at end of #ifdef directive
If you want to check if multiple things are defined, use the second one.
Evan Teran
2009-08-21 14:03:36
Thanks for checking. I'm using Microsoft's compiler and it seems to allow it, but it just didn't seem right to me.
criddell
2009-08-21 14:23:30
+6
A:
You can use the defined operator in the #if directive to use expressions that evaluate to 0 or 1 within a preprocessor line. This saves you from using nested preprocessing directives. The parentheses around the identifier are optional. For example:
#if defined (MAX) && ! defined (MIN)Without using the defined operator, you would have to include the following two directives to perform the above example:
#ifdef max #ifndef min
Svetlozar Angelov
2009-08-21 14:03:50
While what you say is correct, this does not answer the question at all, he asked if the two are the same...they are not.
Evan Teran
2009-08-21 14:07:41
Svetlozar Angelov
2009-08-21 14:15:07
If you have a question, feel free to ask it using the "Ask Question" link at the top of every page. To answer this question, no, it doesn't work. `#if[n]def` takes exactly one identifier as its argument.
James McNellis
2010-09-17 02:24:07