Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.c > #65881

Re: Error messages

From Keith Thompson <kst-u@mib.org>
Newsgroups comp.lang.c
Subject Re: Error messages
Date 2015-07-18 20:59 -0700
Organization None to speak of
Message-ID <lna8ushk5l.fsf@kst-u.example.com> (permalink)
References (1 earlier) <moa2c9$lir$1@dont-email.me> <moabue$e75$1@dont-email.me> <6e397d0b-4082-4915-97e1-0db8020b4241@googlegroups.com> <ln615ihz3g.fsf@kst-u.example.com> <50f83997-f446-4ad1-a418-f35d51f0bd1f@googlegroups.com>

Show all headers | View raw

David Kleinecke <dkleinecke@gmail.com> writes:
> On Friday, July 17, 2015 at 9:25:01 PM UTC-7, Keith Thompson wrote:
>> David Kleinecke <dkleinecke@gmail.com> writes:
>> [...]
>> > A compiler implementation could have a dictionary of all the identifiers
>> > in the Standard Library (and feel free to extend to any other units 
>> > you like) so that if it sees an identifier in a position where it is not
>> > being declared it could search for the identifier in the dictionary and 
>> > add the needed header before proceeding. The compiler must emit a 
>> > message (warning?) teeling you what it did.  
>> >
>> > Anybody ever done that?
>> 
>> Certainly.
>> 
>> $ cat c.c
>> int main(void) {
>>     printf("hello\n");
>> }
>> $ c gcc -c c.c
>> c.c: In function 'main':
>> c.c:2:5: warning: incompatible implicit declaration of built-in function
>> 'printf' [enabled by default]
>>      printf("hello\n");
>        ^
>
> Well at least it recognized that "printf" was a library (built-in!)
> function. It didn't, as I asked, correct the code and continue. The 
> error description is very confusing. At that position the statement 
> cannot be a function declaration because it's inside a compound 
> statement. The compliler seems to think it is the old (now dropped) 
> form of a function definition.

Yes, that's what the error message indicates.  gcc is using the old
"implicit int" rule (but with a warning).  It needs to be able to
recognize it because it still supports C90.  I'm not 100% happy with the
way it does this (even with "-std=c99" or "-std=c11"), but it doesn't
seem to affect anything other than the wording of diagnostics.

> But it does not make the easy repair and continue.

I missed the part where you suggested the compiler should add the needed
header.

Personally, I'm glad it doesn't.  I presume you're not suggesting that
the compiler should modify the source file.  But even having the
compiler *assume* the presence of a missing #include would encourage
sloppy coding.  IMHO gcc is too lax as it is.

>> It happens to do this for "printf" but not for FILE -- though if you
>> write
>> 
>>     FILE *tmp;
>> 
>> without the proper #include, it does recognize that it's a type name.
>  
> It sounds like the libraray identifier data base may only cover
> function names. It is inconvenient for me to run a test just now -
> does it recognize a macro, say, EOF or NULL, without an #include?  

I suspect the existing behavior is based on C90 rules, where functions
declarations may be omitted but other declarations cannot.

I suppose it would be nice if gcc recognized other declarations from
standard headers and tailored its diagnostic messages accordingly.  On
the other hand, if the compiler complains that it doens't recognize NULL
or EOF, the fix is obvious -- at least to me.

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Working, but not speaking, for JetHead Development, Inc.
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"

Back to comp.lang.c | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

Error messages jacobnavia <jacob@jacob.remcomp.fr> - 2015-07-17 02:36 +0200
  Re: Error messages Richard Heathfield <rjh@cpax.org.uk> - 2015-07-17 01:51 +0100
    Re: Error messages Keith Thompson <kst-u@mib.org> - 2015-07-16 18:24 -0700
      Re: Error messages Lőrinczy Zsigmond <nospam@for.me> - 2015-07-17 09:31 +0200
        Re: Error messages Richard Heathfield <rjh@cpax.org.uk> - 2015-07-17 08:35 +0100
          Re: Error messages glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-07-17 09:11 +0000
            Re: Error messages Richard Heathfield <rjh@cpax.org.uk> - 2015-07-17 10:30 +0100
            Re: Error messages Ian Collins <ian-news@hotmail.com> - 2015-07-17 21:44 +1200
              Re: Error messages Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-07-17 12:55 +0100
              Re: Error messages Melzzzzz <mel@zzzzz.com> - 2015-07-17 19:53 +0200
              Re: Error messages glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-07-17 17:55 +0000
                Re: Error messages James Kuyper <jameskuyper@verizon.net> - 2015-07-17 14:19 -0400
            Re: Error messages raltbos@xs4all.nl (Richard Bos) - 2015-07-19 21:44 +0000
        Re: Error messages gazelle@shell.xmission.com (Kenny McCormack) - 2015-07-17 07:38 +0000
          Re: Error messages Noob <root@127.0.0.1> - 2015-07-17 09:58 +0200
            Re: Error messages gazelle@shell.xmission.com (Kenny McCormack) - 2015-07-17 13:32 +0000
      Re: Error messages Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-07-18 11:13 +0100
  Re: Error messages James Kuyper <jameskuyper@verizon.net> - 2015-07-16 22:36 -0400
  Re: Error messages Reinhardt Behm <rbehm@hushmail.com> - 2015-07-17 13:05 +0800
    Re: Error messages jacobnavia <jacob@jacob.remcomp.fr> - 2015-07-17 09:48 +0200
      Re: Error messages David Kleinecke <dkleinecke@gmail.com> - 2015-07-17 19:23 -0700
        Re: Error messages Keith Thompson <kst-u@mib.org> - 2015-07-17 21:24 -0700
          Re: Error messages David Kleinecke <dkleinecke@gmail.com> - 2015-07-18 18:29 -0700
            Re: Error messages Keith Thompson <kst-u@mib.org> - 2015-07-18 20:59 -0700
              Re: Error messages David Kleinecke <dkleinecke@gmail.com> - 2015-07-19 19:22 -0700
            Re: Error messages David Brown <david.brown@hesbynett.no> - 2015-07-21 11:40 +0200
              Compiler conformance (Was: Error messages) gazelle@shell.xmission.com (Kenny McCormack) - 2015-07-21 11:40 +0000
                Re: Compiler conformance Noob <root@127.0.0.1> - 2015-07-21 14:01 +0200
                Re: Compiler conformance gazelle@shell.xmission.com (Kenny McCormack) - 2015-07-21 13:47 +0000
        Re: Error messages Reinhardt Behm <rbehm@hushmail.com> - 2015-07-18 13:38 +0800
    Re: Error messages Keith Thompson <kst-u@mib.org> - 2015-07-17 07:54 -0700
      Re: Error messages raltbos@xs4all.nl (Richard Bos) - 2015-07-19 22:00 +0000
        Re: Error messages Richard Damon <Richard@Damon-Family.org> - 2015-07-19 19:47 -0400
  Re: Error messages jacobnavia <jacob@jacob.remcomp.fr> - 2015-07-17 10:06 +0200
  Re: Error messages Bartc <bc@freeuk.com> - 2015-07-17 12:07 +0100
  Re: Error messages Noob <root@127.0.0.1> - 2015-07-17 13:14 +0200
    Re: Error messages Bartc <bc@freeuk.com> - 2015-07-17 12:40 +0100
  Re: Error messages gwowen <gwowen@gmail.com> - 2015-07-17 04:32 -0700
    Re: Error messages jacobnavia <jacob@jacob.remcomp.fr> - 2015-07-17 14:15 +0200
      Re: Error messages gwowen <gwowen@gmail.com> - 2015-07-17 05:25 -0700
        Re: Error messages Bartc <bc@freeuk.com> - 2015-07-17 13:34 +0100
          Re: Error messages Keith Thompson <kst-u@mib.org> - 2015-07-17 08:07 -0700
        Re: Error messages jacobnavia <jacob@jacob.remcomp.fr> - 2015-07-17 14:38 +0200
          Re: Error messages Martin Shobe <martin.shobe@yahoo.com> - 2015-07-17 08:50 -0500
            Re: Error messages jacobnavia <jacob@jacob.remcomp.fr> - 2015-07-17 16:08 +0200
              Re: Error messages Martin Shobe <martin.shobe@yahoo.com> - 2015-07-17 09:24 -0500
                Re: Error messages James Kuyper <jameskuyper@verizon.net> - 2015-07-17 12:26 -0400
                Re: Error messages Martin Shobe <martin.shobe@yahoo.com> - 2015-07-17 13:19 -0500
                Re: Error messages James Kuyper <jameskuyper@verizon.net> - 2015-07-17 14:28 -0400
                Re: Error messages James Kuyper <jameskuyper@verizon.net> - 2015-07-17 14:43 -0400
                Re: Error messages Bartc <bc@freeuk.com> - 2015-07-17 20:31 +0100
                Re: Error messages Martin Shobe <martin.shobe@yahoo.com> - 2015-07-18 08:41 -0500
                Re: Error messages David Brown <david.brown@hesbynett.no> - 2015-07-21 12:25 +0200
                Re: Error messages James Kuyper <jameskuyper@verizon.net> - 2015-07-21 13:20 -0400
                Re: Error messages David Brown <david.brown@hesbynett.no> - 2015-07-22 00:05 +0200
          Re: Error messages Noob <root@127.0.0.1> - 2015-07-17 16:16 +0200
            Re: Error messages doctor@doctor.nl2k.ab.ca (The Doctor) - 2015-07-17 14:49 +0000
              Re: Error messages Noob <root@127.0.0.1> - 2015-07-17 20:02 +0200
                Re: Error messages The Doctor <doctor@doctor.nl2k.ab.ca> - 2015-07-17 22:24 +0000
                Re: Error messages Noob <root@127.0.0.1> - 2015-07-20 10:46 +0200
                Re: Error messages doctor@doctor.nl2k.ab.ca (The Doctor) - 2015-07-20 14:59 +0000
          Re: Error messages Keith Thompson <kst-u@mib.org> - 2015-07-17 08:25 -0700
      Re: Error messages raltbos@xs4all.nl (Richard Bos) - 2015-07-19 22:07 +0000
  Re: Error messages Ed Prochak <edprochak@gmail.com> - 2015-07-17 20:11 -0700

csiph-web