Hello, I have the source code of an application written in C++ and I just want to comment something using:
#ifdef 0
...
#endif
And I get this error
error: macro names must be identifiers
Why is this happening this?. Thanks
views:
4648answers:
2
+6
A:
Use the following to evaluate an expression (constant 0 evaluates to false).
#if 0
...
#endif
tvanfosson
2009-01-09 01:33:51
+5
A:
The #ifdef directive is used to check if a pre-processor symbol is defined. It's possible that your C compiler allows pre-processor symbols that start with a digit (but unlikely since it would seriously screw up the parser) and your C++ compiler doesn't.
The correct form for using the pre-processor to block out code is:
#if 0
: : :
#endif
or
#ifdef NO_CHANCE_THAT_THIS_SYMBOL_WILL_EVER_EXIST
: : :
#endif
paxdiablo
2009-01-09 01:38:49
I have some code that I compile occasionally that is compiled with -DNEVER_USED. I haven't investigated why - I hate to guess.
Jonathan Leffler
2009-01-09 02:27:43
@Pax: actually, it is very unlikely that the C compiler allows the notation - it would be erroneous if it did. See also my comment to the question. I suggest removing your sentence "It's likely that...".
Jonathan Leffler
2009-01-09 06:19:08
Not all C compilers are ANSI-compliant. I've used plenty of embedded compilers that allow all sorts of trickiness like that. But I'll fix it.
paxdiablo
2009-01-09 06:29:34