RE: problem with macro expansion in GCC

RE: problem with macro expansion in GCC

[David Korn]

   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 ##.

       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: Puneet Singhal [ mailto:puneet@opussoft.com ]
>Sent: 06 February 2001 04:54
>To: Dhanabal Ekambaram; gcc-help@gcc.gnu.org
>Subject: RE: problem with macro expansion in GCC
>Importance: High
>
>
>I tried it on my machine (solaris sparc 7 and gcc 2.95.2)
>I get " y .ptr" instead of desirable "y.ptr".
>
>Even I cant figure out why?
>
>Puneet
>
>>-----Original Message-----
>>From: gcc-help-owner@gcc.gnu.org [ mailto:gcc-help-owner@gcc.gnu.org]On
>>Behalf Of Dhanabal Ekambaram
>>Sent: Tuesday, February 06, 2001 8:36 AM
>>To: 'gcc-help@gcc.gnu.org'
>>Subject: problem with macro expansion in GCC
>>
>>
>>Hi,
>>
>>When I use
>>
>>#define XXX(N)  N.ptr
>>
>>XXX(y) gets transformed to " y.ptr" instead of "y.ptr".
>>I am not sure why i am getting this leading space in the 
>expanded string.
>>
>>Can anybody help me to eliminate this problem?
>>
>>Thanks,
>>dhanabal
>
>


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RE: problem with macro expansion in GCC

[David Korn]

>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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This footnote also confirms that this email message has been swept by
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Re: problem with macro expansion in GCC

[Alexandre Oliva]

On Feb  6, 2001, Dhanabal Ekambaram <Dhanabal@Zambeel.com> wrote:

> #define XXX(N)  N.ptr

> XXX(y) gets transformed to " y.ptr" instead of "y.ptr".

That's to prevent unwanted token pasting, if XXX(y) happens to be
preceded by something that might be seem like the same token.  This
would unlikely be the case for this particular macro, but how is the
preprocessor to know that?

In any case, the extra space shouldn't be a problem for you; the
compiler will simply discard it.

-- 
Alexandre Oliva   Enjoy Guarana', see http://www.ic.unicamp.br/~oliva/
Red Hat GCC Developer                  aoliva@{cygnus.com, redhat.com}
CS PhD student at IC-Unicamp        oliva@{lsd.ic.unicamp.br, gnu.org}
Free Software Evangelist    *Please* write to mailing lists, not to me

RE: problem with macro expansion in GCC

[Dhanabal Ekambaram]

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;

Thanks,
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 ##.

RE: problem with macro expansion in GCC

[Puneet Singhal]

I tried it on my machine (solaris sparc 7 and gcc 2.95.2)
I get " y .ptr" instead of desirable "y.ptr".

Even I cant figure out why?

Puneet

>-----Original Message-----
>From: gcc-help-owner@gcc.gnu.org [ mailto:gcc-help-owner@gcc.gnu.org]On
>Behalf Of Dhanabal Ekambaram
>Sent: Tuesday, February 06, 2001 8:36 AM
>To: 'gcc-help@gcc.gnu.org'
>Subject: problem with macro expansion in GCC
>
>
>Hi,
>
>When I use
>
>#define XXX(N)  N.ptr
>
>XXX(y) gets transformed to " y.ptr" instead of "y.ptr".
>I am not sure why i am getting this leading space in the expanded string.
>
>Can anybody help me to eliminate this problem?
>
>Thanks,
>dhanabal

problem with macro expansion in GCC

[Dhanabal Ekambaram]

Hi,

When I use

#define XXX(N)  N.ptr

XXX(y) gets transformed to " y.ptr" instead of "y.ptr".
I am not sure why i am getting this leading space in the expanded string.

Can anybody help me to eliminate this problem?

Thanks,
dhanabal