[cfe-commits] r172643 - /cfe/trunk/docs/LanguageExtensions.rst

[Aaron Ballman]

Yeah, I didn't want to get too technical because I think it gets even
more confusing at that point.  It can be macro expanded, so long as
the expansion happens as part of the expression in a #if or #elif.
Put another way, it can't be used as a constant expression outside of
a preprocessor directive.

If anyone can think of a better wording for the docs, I'd be all ears!

~Aaron

On Wed, Jan 16, 2013 at 3:01 PM, Jordan Rose <jordan_rose at apple.com> wrote:
> This confused me because I thought it implied that this was disallowed:
>
> #define HAS_STDIO __has_include(<stdio.h>)
> #if HAS_STDIO
> // do something
> #endif
>
> But this is still allowed. I'm not sure how to rephrase this to make it clearer, though.
>
>
> On Jan 16, 2013, at 11:51 , Aaron Ballman <aaron at aaronballman.com> wrote:
>
>> Author: aaronballman
>> Date: Wed Jan 16 13:51:19 2013
>> New Revision: 172643
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=172643&view=rev
>> Log:
>> Adding verbiage to the Language Extensions document about __has_include and __has_include_next only being allowed within preprocessor directives.
>>
>> Modified:
>>    cfe/trunk/docs/LanguageExtensions.rst
>>
>> Modified: cfe/trunk/docs/LanguageExtensions.rst
>> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/docs/LanguageExtensions.rst?rev=172643&r1=172642&r2=172643&view=diff
>> ==============================================================================
>> --- cfe/trunk/docs/LanguageExtensions.rst (original)
>> +++ cfe/trunk/docs/LanguageExtensions.rst Wed Jan 16 13:51:19 2013
>> @@ -140,7 +140,8 @@
>> Not all developments systems have the same include files.  The
>> :ref:`langext-__has_include` and :ref:`langext-__has_include_next` macros allow
>> you to check for the existence of an include file before doing a possibly
>> -failing ``#include`` directive.
>> +failing ``#include`` directive.  Include file checking macros must be used
>> +as expressions in #if or #elif preprocessing directives.
>>
>> .. _langext-__has_include:
>>
>>
>>
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