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how warp a name by spaces in preprocessor mode

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  how warp a name by spaces in preprocessor mode Arek <oczykota@gmail.com> - 2012-03-21 08:20 -0700
    Re: how warp a name by spaces in preprocessor mode jt@toerring.de (Jens Thoms Toerring) - 2012-03-21 16:07 +0000
      Re: how warp a name by spaces in preprocessor mode Arek <oczykota@gmail.com> - 2012-03-21 09:41 -0700
        Re: how warp a name by spaces in preprocessor mode James Kuyper <jameskuyper@verizon.net> - 2012-03-21 13:47 -0400

#18929 — how warp a name by spaces in preprocessor mode

Hi,
  How can I warp a name by space using preprocessor?
for example:
How write macro:
GET_LAST_ELEMENT(A B C D)
that it return
D

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#18931

Arek <oczykota@gmail.com> wrote:
>   How can I warp a name by space using preprocessor?
> for example:
> How write macro:
> GET_LAST_ELEMENT(A B C D)

The arghuments of a macro must be separated by commas, so this
one won't work. And what's the "name" here?

> that it return

A macro doesn't return anything, it's not a function but does
just textual replacement.

> D

You can have macro like

#define GET_LAST)F_FOUR( A, B, C, D ) D

and when called e.g. as

   int x = GET_LAST_OF_FOUR( 1, 2, 3, 4 );

this will be replaced by

   int x = 4;

But I have a feeling that this isn't what you had in mind...

If you're looking for a macro that takes apart a string,
e.g. something that, when given an argument of "A B C D",
will replace it by "D" (the part of the string after the
last space) then you're rather likely out of luck, better
write a function.
                           Regards, Jens
-- 
  \   Jens Thoms Toerring  ___      jt@toerring.de
   \__________________________      http://toerring.de

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#18932

On 21 Mar, 17:07 (Jens Thoms Toerring) wrote:

> If you're looking for a macro that takes apart a string,
> e.g. something that, when given an argument of "A B C D",
> will replace it by "D" (the part of the string after the
> last space) then you're rather likely out of luck, better
> write a function.

yes. something like that.
if i make:
#define w _a _b _c
then w will be replaced by "_a _b _c"
I want to have macro
GET_LAST_ELEMENT(w)
which will be replaced by _c

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#18933

On 03/21/2012 12:41 PM, Arek wrote:
> On 21 Mar, 17:07 (Jens Thoms Toerring) wrote:
> 
>> If you're looking for a macro that takes apart a string,
>> e.g. something that, when given an argument of "A B C D",
>> will replace it by "D" (the part of the string after the
>> last space) then you're rather likely out of luck, better
>> write a function.
> 
> yes. something like that.
> if i make:
> #define w _a _b _c
> then w will be replaced by "_a _b _c"
> I want to have macro
> GET_LAST_ELEMENT(w)
> which will be replaced by _c

As he said, you're out of luck - C's preprocessing capabilities are
quite limited, they're not powerful enough to do that. Possibly you're
taking the wrong approach to this; possibly C isn't the right language
for what you want to do. You might need to use some other preprocessor
such as m4, or you might need to write your own preprocessor program to
automatically generate the C code that you want GET_LAST_ELEMENT() to
generate.

If you could give some context, we might be able to suggest an
alternative approach. You can't #define GET_LAST_ELEMENT() to work the
way you want it to, but could you provide some example code that shows
us what you would want to do with it, if it could be #defined? The code
should be "real" enough to make it clear to us, not only about what you
want GET_LAST_ELEMENT() to do, but more importantly, why you want it to
do that.

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