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Re: Multi-instructions macro and compiler warning

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On 10/17/11 09:49 AM, Keith Thompson wrote:
> Jean-Christophe<5.d@free.fr>  writes:
>> On 16 oct, 09:09, pozz
>>> I received many warning messages of the type
>>>     W1207C: conditional expression is constant: dowhile
>>> Those messages refer to multi-instructions macros defined as below:
>>>     #define MACRO(a, b)  do { foo(a); bar(b); } while(0)
>>
>> Why not
>>
>> #define MACRO(a,b)  { foo(a); bar(b); }
>
> See question 10.4 of the comp.lang.c FAQ,<http://c-faq.com/>.
>
> The problem is that if you write:
>
>      if(cond)
>          MACRO(arg1, arg2);
>      else
>      /* some other code */
>
> you get a syntax error due to the extra semicolon.  The
>      do /* ... */ while (0)
> idiom avoids that problem.

So do functions!

-- 
Ian Collins

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Multi-instructions macro and compiler warning pozz <pozzugno@gmail.com> - 2011-10-16 09:09 +0200
  Re: Multi-instructions macro and compiler warning Ian Collins <ian-news@hotmail.com> - 2011-10-16 20:31 +1300
    Re: Multi-instructions macro and compiler warning pozz <pozzugno@gmail.com> - 2011-10-16 09:41 +0200
      Re: Multi-instructions macro and compiler warning Ian Collins <ian-news@hotmail.com> - 2011-10-16 20:49 +1300
        Re: Multi-instructions macro and compiler warning pozz <pozzugno@gmail.com> - 2011-10-16 10:16 +0200
          Re: Multi-instructions macro and compiler warning Ian Collins <ian-news@hotmail.com> - 2011-10-16 23:09 +1300
            Re: Multi-instructions macro and compiler warning pozz <pozzugno@gmail.com> - 2011-10-17 02:37 -0700
              Re: Multi-instructions macro and compiler warning Ian Collins <ian-news@hotmail.com> - 2011-10-17 23:04 +1300
              Re: Multi-instructions macro and compiler warning Ben Bacarisse <ben.usenet@bsb.me.uk> - 2011-10-17 11:06 +0100
                Re: Multi-instructions macro and compiler warning pozz <pozzugno@gmail.com> - 2011-10-17 03:23 -0700
              Re: Multi-instructions macro and compiler warning Keith Thompson <kst-u@mib.org> - 2011-10-17 12:30 -0700
      Re: Multi-instructions macro and compiler warning "BartC" <bc@freeuk.com> - 2011-10-16 12:47 +0100
        Re: Multi-instructions macro and compiler warning Jorgen Grahn <grahn+nntp@snipabacken.se> - 2011-10-16 22:16 +0000
        Re: Multi-instructions macro and compiler warning pozz <pozzugno@gmail.com> - 2011-10-17 02:42 -0700
          Re: Multi-instructions macro and compiler warning "BartC" <bc@freeuk.com> - 2011-10-17 13:10 +0100
      Re: Multi-instructions macro and compiler warning bert <bert.hutchings@btinternet.com> - 2011-10-16 05:33 -0700
  Re: Multi-instructions macro and compiler warning Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-10-16 09:02 -0400
  Re: Multi-instructions macro and compiler warning "christian.bau" <christian.bau@cbau.wanadoo.co.uk> - 2011-10-16 07:40 -0700
    Re: Multi-instructions macro and compiler warning ImpalerCore <jadill33@gmail.com> - 2011-10-17 08:07 -0700
      Re: Multi-instructions macro and compiler warning "christian.bau" <christian.bau@cbau.wanadoo.co.uk> - 2011-10-17 09:25 -0700
        Re: Multi-instructions macro and compiler warning James Kuyper <jameskuyper@verizon.net> - 2011-10-17 12:58 -0400
          Re: Multi-instructions macro and compiler warning Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-10-18 07:43 -0400
            Re: Multi-instructions macro and compiler warning Keith Thompson <kst-u@mib.org> - 2011-10-18 11:52 -0700
        Re: Multi-instructions macro and compiler warning ImpalerCore <jadill33@gmail.com> - 2011-10-17 10:41 -0700
  Re: Multi-instructions macro and compiler warning Jean-Christophe <5.d@free.fr> - 2011-10-16 10:02 -0700
    Re: Multi-instructions macro and compiler warning Kleuskes & Moos <kleuske@somewhere.else.net> - 2011-10-16 17:44 +0000
    Re: Multi-instructions macro and compiler warning Keith Thompson <kst-u@mib.org> - 2011-10-16 13:49 -0700
      Re: Multi-instructions macro and compiler warning Ian Collins <ian-news@hotmail.com> - 2011-10-17 10:00 +1300
  Re: Multi-instructions macro and compiler warning Kenneth Brody <kenbrody@spamcop.net> - 2011-10-17 12:50 -0400
    Re: Multi-instructions macro and compiler warning "Morris Keesan" <mkeesan@post.harvard.edu> - 2011-10-17 14:50 -0400

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