Re: 'Amalgamated' source code

From	Ben Bacarisse <ben.usenet@bsb.me.uk>
Newsgroups	comp.lang.c
Subject	Re: 'Amalgamated' source code
Date	2017-01-05 19:33 +0000
Organization	A noiseless patient Spider
Message-ID	<87k2a9i9ne.fsf@bsb.me.uk> (permalink)
References	(10 earlier) <o4io7d$c95$1@dont-email.me> <c901fe2c-600f-430c-be7c-3bfc274e06e3@googlegroups.com> <8b7b2773-2a60-44c5-a9f4-e5fa23eff966@googlegroups.com> <87bmvlk2cr.fsf@bsb.me.uk> <o4m0c3$saf$1@dont-email.me>

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BartC <bc@freeuk.com> writes:

> On 05/01/2017 14:28, Ben Bacarisse wrote:
>> Thiago Adams <thiago.adams@gmail.com> writes:
>> <snip>
>>> I did one more sample to see what happens:
>>>
>>> #define M(a) X##a
>>> #define M2(a, b) #a a b
>>>
>>> M2(  M ( 1), M(1))
>>>
>>> VC++ preprocessor output:
>>>
>>> "M ( 1)" X1 X1
>>>
>>> The same argument 'a' for macro can or not be expanded before
>>> the macro invocation.
>>>
>>> Today I keep a map "parameter-name:a" - > "expanded:X1"
>>>
>>> To fix my preprocessor I will keep both:
>>>
>>>   "parameter-name:a" - > ["expanded:X1", "not expanded:M ( 1)"]
>>>
>>> and use the appropriated value depending on #a or a.
>>
>> That seems like a very odd way to do it.  Have you read what the C
>> standard says about macro expansion?  It explains the algorithm quite
>> well, in my option.
>
> I couldn't make head or tail of it (6.10.3.1):
>
> "A parameter in the replacement list, unless ... is replaced by the
> corresponding argument after all macros contained therein have been
> expanded. Before being substituted, each argument’s preprocessing
> tokens are completely macro replaced as if they formed the rest of the
> preprocessing file; no other preprocessing tokens are available."
>
> What does the second sentence mean; is it just restating what happens
> in the first?

It says a bit more than the first.  In particular it says the each
argument's token list is treated separately and like a file on it's own.
Maybe you never thought otherwise but perhaps that's been the source of
some confusion in that past.

> And that's not all of it; the process continues in
> 6.10.3.4.
>
> Here's how the gnu CPP docs explain it; I think this covers all of it
> apart from # and ##:

But # and ## are the problem here.  It's much easier to explain
expansion while ignoring or glossing over # and ##.

> "All arguments to a macro are completely macro-expanded before they
> are substituted into the macro body. After substitution, the complete
> text is scanned again for macros to expand, including the arguments."
>
> Of course I will have to try out this second scheme to see if handles
> all the tricky examples.

It's not hard to describe in broad terms.  The problem is saying exactly
what happens and in what order.  If the gcc docs helps then I think
that's great.

-- 
Ben.

Thread

'Amalgamated' source code BartC <bc@freeuk.com> - 2017-01-03 15:14 +0000
  Re: 'Amalgamated' source code Thiago Adams <thiago.adams@gmail.com> - 2017-01-03 08:47 -0800
    Re: 'Amalgamated' source code BartC <bc@freeuk.com> - 2017-01-03 19:47 +0000
      Re: 'Amalgamated' source code Thiago Adams <thiago.adams@gmail.com> - 2017-01-03 12:48 -0800
        Re: 'Amalgamated' source code BartC <bc@freeuk.com> - 2017-01-03 21:36 +0000
          Re: 'Amalgamated' source code Thiago Adams <thiago.adams@gmail.com> - 2017-01-03 16:01 -0800
            Re: 'Amalgamated' source code Keith Thompson <kst-u@mib.org> - 2017-01-03 16:26 -0800
              Re: 'Amalgamated' source code Thiago Adams <thiago.adams@gmail.com> - 2017-01-03 18:00 -0800
                Re: 'Amalgamated' source code Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-01-04 03:34 +0000
                Re: 'Amalgamated' source code Thiago Adams <thiago.adams@gmail.com> - 2017-01-04 03:31 -0800
                Re: 'Amalgamated' source code BartC <bc@freeuk.com> - 2017-01-04 12:03 +0000
                Re: 'Amalgamated' source code Thiago Adams <thiago.adams@gmail.com> - 2017-01-04 05:00 -0800
                Re: 'Amalgamated' source code Thiago Adams <thiago.adams@gmail.com> - 2017-01-05 02:38 -0800
                Re: 'Amalgamated' source code Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-01-05 14:28 +0000
                Re: 'Amalgamated' source code supercat@casperkitty.com - 2017-01-05 08:20 -0800
                Re: 'Amalgamated' source code Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-01-05 17:05 +0000
                Re: 'Amalgamated' source code supercat@casperkitty.com - 2017-01-05 10:11 -0800
                Re: 'Amalgamated' source code Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-01-05 19:46 +0000
                Re: 'Amalgamated' source code Thiago Adams <thiago.adams@gmail.com> - 2017-01-05 12:15 -0800
                Re: 'Amalgamated' source code Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-01-05 21:54 +0000
                Re: 'Amalgamated' source code BartC <bc@freeuk.com> - 2017-01-05 17:40 +0000
                Re: 'Amalgamated' source code Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-01-05 19:33 +0000
            Re: 'Amalgamated' source code BartC <bc@freeuk.com> - 2017-01-04 10:53 +0000
          Re: 'Amalgamated' source code Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-01-04 01:51 +0000
        Re: 'Amalgamated' source code BartC <bc@freeuk.com> - 2017-01-04 11:54 +0000
          Re: 'Amalgamated' source code Thiago Adams <thiago.adams@gmail.com> - 2017-01-04 05:57 -0800
            Re: 'Amalgamated' source code BartC <bc@freeuk.com> - 2017-01-04 14:20 +0000
            Re: 'Amalgamated' source code BartC <bc@freeuk.com> - 2017-01-04 15:07 +0000
              Re: 'Amalgamated' source code Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-01-04 15:34 +0000
                Re: 'Amalgamated' source code Thiago Adams <thiago.adams@gmail.com> - 2017-01-04 08:03 -0800
                Re: 'Amalgamated' source code Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-01-04 17:09 +0000
                Re: 'Amalgamated' source code bart4858@gmail.com - 2017-01-04 08:54 -0800
                Re: 'Amalgamated' source code Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-01-04 17:22 +0000
              Re: 'Amalgamated' source code Thiago Adams <thiago.adams@gmail.com> - 2017-01-04 07:55 -0800
                Re: 'Amalgamated' source code BartC <bc@freeuk.com> - 2017-01-05 18:04 +0000
                Re: 'Amalgamated' source code Thiago Adams <thiago.adams@gmail.com> - 2017-01-05 11:50 -0800
  Re: 'Amalgamated' source code Jorgen Grahn <grahn+nntp@snipabacken.se> - 2017-01-04 16:29 +0000
    Re: 'Amalgamated' source code bart4858@gmail.com - 2017-01-04 09:15 -0800
      Re: 'Amalgamated' source code Ian Collins <ian-news@hotmail.com> - 2017-01-05 08:33 +1300
        Re: 'Amalgamated' source code BartC <bc@freeuk.com> - 2017-01-04 20:26 +0000
          Re: 'Amalgamated' source code supercat@casperkitty.com - 2017-01-04 13:09 -0800
          Re: 'Amalgamated' source code Ian Collins <ian-news@hotmail.com> - 2017-01-05 10:21 +1300
            Re: 'Amalgamated' source code supercat@casperkitty.com - 2017-01-04 13:51 -0800
            Re: 'Amalgamated' source code BartC <bc@freeuk.com> - 2017-01-04 22:02 +0000
              Re: 'Amalgamated' source code Ian Collins <ian-news@hotmail.com> - 2017-01-05 11:15 +1300
      Re: 'Amalgamated' source code Jorgen Grahn <grahn+nntp@snipabacken.se> - 2017-01-07 06:38 +0000
        Re: 'Amalgamated' source code BartC <bc@freeuk.com> - 2017-01-07 11:35 +0000
    Re: 'Amalgamated' source code supercat@casperkitty.com - 2017-01-04 09:53 -0800
    Re: 'Amalgamated' source code Malcolm McLean <malcolm.mclean5@btinternet.com> - 2017-01-04 11:50 -0800
    Re: 'Amalgamated' source code raltbos@xs4all.nl (Richard Bos) - 2017-01-10 01:34 +0000
      Re: 'Amalgamated' source code Malcolm McLean <malcolm.mclean5@btinternet.com> - 2017-01-10 01:59 -0800
      Re: 'Amalgamated' source code Les Cargill <lcargill99@comcast.com> - 2017-01-10 06:55 -0600
      Re: 'Amalgamated' source code Richard Heathfield <rjh@cpax.org.uk> - 2017-01-10 14:48 +0000
  Re: 'Amalgamated' source code Thiago Adams <thiago.adams@gmail.com> - 2017-04-26 07:17 -0700

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