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Groups > comp.lang.c > #101324
| From | BartC <bc@freeuk.com> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: Macro Expansion |
| Date | 2017-01-09 01:11 +0000 |
| Organization | A noiseless patient Spider |
| Message-ID | <o4unsf$p2j$1@dont-email.me> (permalink) |
| References | <o4rcbl$4cp$1@dont-email.me> <o4ufvd$geq$1@z-news.wcss.wroc.pl> <o4ujb6$d72$1@dont-email.me> |
On 08/01/2017 23:53, BartC wrote:
> On 08/01/2017 22:54, antispam@math.uni.wroc.pl wrote:
>> BartC <bc@freeuk.com> wrote:
>
>>> * The result is now scanned again looking for new macros to expand.
>>> However, once any name (eg. M and W) has been expanded once, it is
>>> never expanded again (in a subsequent pass). So only XX is changed
>>> to result in:
>>>
>>> 10 20 "10" 99 M(a,b) W+W+20+x
>>
>> AFAICS this is your interetation, which is mostly correct but
>> in corner cases may produce wrong result and seem to be much
>> less efficient then what standard says:
>>
>> : After all parameters in the replacement list have been substituted
>> : and # and ## processing has taken place, all placemarker preprocessing
>> : tokens are removed. The resulting preprocessing token sequence is
>> : then rescanned, along with all subsequent preprocessing tokens of
>> : the source file, for more macro names to replace.
>>
>> So, after macro expanded parameters are substituted and # and ##
>> handling is done you simply prepend the result to source text
>> following macro call and start reading from the start of resulting
>> token list. In other words there are _no_ repeated rescanning,
>> rescanning is done just once and during rescanning you may have
>> macro call which begins withing replacement list but ends in the
>> source text.
Yes, this is an good example of that:
#define A(x,y) if(x==y)
#define B A(
int main(void){
B 10,20);
}
The expanded code should be 'if(10==20)'. But out of six compilers I
tried, 3 had problems. (One crashed, one ran out of memory, another -
MSVC 2008 - reported an error about A not having enough arguments.
However this variation:
#define A(x,y) if(x==y)
#define B A
int main(void){
B (10,20);
}
was generally OK. The new macro call is still split like this:
A / (10,20) # A in replacement sequence, rest in main source
but that seems to be less objectionable.
Also, K&R2, page 230, says this:
"In both kinds of macro, the replacement token sequence is repeatedly
rescanned for more defined identifiers." (Then going on about only
replacing each identifier once.)
I think I might go with my current scheme for now (which has a tweak to
fix the second case above where the replacement text ends with a new
macro name, and the "(...)" follows in the main text). Because I've
already solved the problems with controlling macro replacement, which
will be harder when it's mixed with the main text.
(I need to get on with the rest of my compiler and can live with a not
quite perfect preprocessor until I can return to it later on when
everything else is finished, and try a different approach. I think if it
was OK for Microsoft - in 2008 anyway - it'll do for me!)
--
Bartc
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Macro Expansion BartC <bc@freeuk.com> - 2017-01-07 18:35 +0000
Re: Macro Expansion Thiago Adams <thiago.adams@gmail.com> - 2017-01-07 11:23 -0800
Re: Macro Expansion Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-01-07 21:28 +0000
Re: Macro Expansion Siri Cruise <chine.bleu@yahoo.com> - 2017-01-07 11:45 -0800
Re: Macro Expansion BartC <bc@freeuk.com> - 2017-01-07 20:16 +0000
Re: Macro Expansion Siri Cruise <chine.bleu@yahoo.com> - 2017-01-07 12:23 -0800
Re: Macro Expansion BartC <bc@freeuk.com> - 2017-01-07 20:31 +0000
Re: Macro Expansion Siri Cruise <chine.bleu@yahoo.com> - 2017-01-07 12:42 -0800
Re: Macro Expansion Ian Collins <ian-news@hotmail.com> - 2017-01-08 14:42 +1300
Re: Macro Expansion BartC <bc@freeuk.com> - 2017-01-08 13:18 +0000
Re: Macro Expansion BartC <bc@freeuk.com> - 2017-01-07 20:15 +0000
Re: Macro Expansion Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-01-07 20:42 +0000
Re: Macro Expansion BartC <bc@freeuk.com> - 2017-01-07 22:50 +0000
Re: Macro Expansion Ian Collins <ian-news@hotmail.com> - 2017-01-08 11:59 +1300
Re: Macro Expansion Malcolm McLean <malcolm.mclean5@btinternet.com> - 2017-01-07 15:10 -0800
Re: Macro Expansion supercat@casperkitty.com - 2017-01-07 17:24 -0800
Re: Macro Expansion Tim Rentsch <txr@alumni.caltech.edu> - 2017-01-15 21:55 -0800
Re: Macro Expansion supercat@casperkitty.com - 2017-01-16 09:06 -0800
Re: Macro Expansion Tim Rentsch <txr@alumni.caltech.edu> - 2017-01-31 08:51 -0800
Re: Macro Expansion supercat@casperkitty.com - 2017-01-31 13:06 -0800
Re: Macro Expansion Tim Rentsch <txr@alumni.caltech.edu> - 2017-02-03 07:49 -0800
Re: Macro Expansion supercat@casperkitty.com - 2017-02-03 12:03 -0800
Re: Macro Expansion Tim Rentsch <txr@alumni.caltech.edu> - 2017-02-09 09:00 -0800
Re: Macro Expansion Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-01-08 01:37 +0000
Re: Macro Expansion Jean-Marc Bourguet <jm@bourguet.org> - 2017-01-08 10:22 +0100
Re: Macro Expansion Thiago Adams <thiago.adams@gmail.com> - 2017-01-07 12:18 -0800
Re: Macro Expansion BartC <bc@freeuk.com> - 2017-01-07 20:28 +0000
Re: Macro Expansion Thiago Adams <thiago.adams@gmail.com> - 2017-01-07 12:36 -0800
Re: Macro Expansion BartC <bc@freeuk.com> - 2017-01-07 22:59 +0000
Re: Macro Expansion Thiago Adams <thiago.adams@gmail.com> - 2017-01-08 00:20 -0800
Re: Macro Expansion BartC <bc@freeuk.com> - 2017-01-08 13:30 +0000
Re: Macro Expansion BartC <bc@freeuk.com> - 2017-01-10 14:00 +0000
Re: Macro Expansion Thiago Adams <thiago.adams@gmail.com> - 2017-01-10 07:43 -0800
Re: Macro Expansion BartC <bc@freeuk.com> - 2017-01-10 17:47 +0000
Re: Macro Expansion Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-01-10 22:49 +0000
Re: Macro Expansion BartC <bc@freeuk.com> - 2017-01-10 23:28 +0000
Re: Macro Expansion "James R. Kuyper" <jameskuyper@verizon.net> - 2017-01-10 18:51 -0500
Re: Macro Expansion BartC <bc@freeuk.com> - 2017-01-11 00:06 +0000
Re: Macro Expansion BartC <bc@freeuk.com> - 2017-01-10 20:30 +0000
Re: Macro Expansion Thiago Adams <thiago.adams@gmail.com> - 2017-04-26 10:04 -0700
Re: Macro Expansion Keith Thompson <kst-u@mib.org> - 2017-04-26 12:00 -0700
Re: Macro Expansion Thiago Adams <thiago.adams@gmail.com> - 2017-04-26 12:24 -0700
Re: Macro Expansion bartc <bc@freeuk.com> - 2017-04-26 20:12 +0100
Re: Macro Expansion Thiago Adams <thiago.adams@gmail.com> - 2017-04-26 12:34 -0700
Re: Macro Expansion jameskuyper@verizon.net - 2017-04-26 13:46 -0700
Re: Macro Expansion Jean-Marc Bourguet <jm@bourguet.org> - 2017-01-08 10:13 +0100
Re: Macro Expansion BartC <bc@freeuk.com> - 2017-01-08 13:10 +0000
Re: Macro Expansion Jean-Marc Bourguet <jm@bourguet.org> - 2017-01-08 15:51 +0100
Re: Macro Expansion BartC <bc@freeuk.com> - 2017-01-08 17:17 +0000
Re: Macro Expansion supercat@casperkitty.com - 2017-01-08 11:04 -0800
Re: Macro Expansion Malcolm McLean <malcolm.mclean5@btinternet.com> - 2017-01-08 11:10 -0800
Re: Macro Expansion supercat@casperkitty.com - 2017-01-08 14:08 -0800
Re: Macro Expansion BartC <bc@freeuk.com> - 2017-01-08 19:49 +0000
Re: Macro Expansion supercat@casperkitty.com - 2017-01-08 14:17 -0800
Re: Macro Expansion BartC <bc@freeuk.com> - 2017-01-08 19:19 +0000
Re: Macro Expansion Jean-Marc Bourguet <jm@bourguet.org> - 2017-01-08 21:43 +0100
Re: Macro Expansion supercat@casperkitty.com - 2017-01-08 10:43 -0800
Re: Macro Expansion Keith Thompson <kst-u@mib.org> - 2017-01-08 12:39 -0800
Re: Macro Expansion antispam@math.uni.wroc.pl - 2017-01-08 22:54 +0000
Re: Macro Expansion "James R. Kuyper" <jameskuyper@verizon.net> - 2017-01-08 18:36 -0500
Re: Macro Expansion antispam@math.uni.wroc.pl - 2017-01-09 01:15 +0000
Re: Macro Expansion "James R. Kuyper" <jameskuyper@verizon.net> - 2017-01-08 20:49 -0500
Re: Macro Expansion BartC <bc@freeuk.com> - 2017-01-08 23:53 +0000
Re: Macro Expansion BartC <bc@freeuk.com> - 2017-01-09 01:11 +0000
Re: Macro Expansion antispam@math.uni.wroc.pl - 2017-01-09 01:31 +0000
Re: Macro Expansion BartC <bc@freeuk.com> - 2017-01-10 11:28 +0000
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