RE: problem with macro expansion in GCC

[David Korn <dkorn at pixelpower dot com>]

>Hi David & Puneet,
>
>Thanks for the comments.
>
>I did try with concatenation already. It takes care of
>the space between "N" and the ".".  But, I do get
>a leading space wherever I use this macro.
>
>If I have 
>x = a.XXX(b);
>
>I expect it to change to
>x = a.b.ptr;
>
>but, it changes to
>x = a. b.ptr;
>

   Hi Dhanabal,

 You have to use concatenation *again* to join "a" and "XXX(b)"; it is 
part of how the preprocessor is defined to work that it won't just 
concatenate tokens like that.  Macro definitions are special items and
the spaces are introduced deliberately to prevent them from unexpectedly
joining onto other things.

 x = CAT(a, XXX(b));

        DaveK
-- 
we are not seats or eyeballs or end users or consumers.
we are human beings - and our reach exceeds your grasp.
                    deal with it.                      - cluetrain.org 

>-----Original Message-----
>From: Dhanabal Ekambaram [mailto:Dhanabal@Zambeel.com]
>Sent: 06 February 2001 18:32
>To: David Korn; 'Puneet Singhal'; gcc-help@gcc.gnu.org
>Subject: RE: problem with macro expansion in GCC
>
>
>dhanabal
>
>>   What happens if you try
>>#define XXX(N) N ## .ptr  
>>
>> or perhaps
>>
>>#define CAT(a, b) a ## b
>>#define XXX(N)    CAT(N, .ptr)
>> 
>>  One or other of those should work.  You can't ask macros to 
>concatenate
>>two strings just by writing them next to each other, you have to use
>>the pre-processor pasting command ##.
>


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