Re: What a stupid gcc!

From	"BartC" <bc@freeuk.com>
Newsgroups	comp.lang.c
Subject	Re: What a stupid gcc!
Date	2012-06-19 18:01 +0100
Organization	A noiseless patient Spider
Message-ID	<jrqb9i$oop$1@dont-email.me> (permalink)
References	(8 earlier) <slrn3vfsju0eu7.9cu.ike@sverige.freeshell.org> <jrpino$1lj$1@dont-email.me> <0.0ff9867a492014af7e6b.20120619134530BST.87395rsc5x.fsf@bsb.me.uk> <jrq23v$rtv$1@dont-email.me> <slrn3vfsju19bv.j4j.ike@iceland.freeshell.org>

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"Ike Naar" <ike@iceland.freeshell.org> wrote in message
news:slrn3vfsju19bv.j4j.ike@iceland.freeshell.org...
> On 2012-06-19, BartC <bc@freeuk.com> wrote:

>> if my understanding of how
>> it works is correct, the following code is wrong:
>>
>> void fn(void){
>> int x=1,y=2;
>>
>> if (x) {
>>  int z=3;
>> }
>> else {
>>  z=4;
>
> This is a syntax error; this z is undeclared.
> The scope of the previous z ended at the closing brace of the block
> where it was declared.
>
> It is also a design error; if z is used in both branches of the
> if statement, and also in the printf after the if statement,
> it does not make sense to declare it in the first branch of the if
> statement,
> it has to be declared at the level of the function body (where
> the declarations of x and y are).

So, this is a restriction on the ability to be able to declare variables
'anywhere'. Either it's an immediate error (a later use of the variable
brings it up), or the later variable mistakenly uses a more global version
(for example, a file-scope variable), or it works, but subsequent editing
removes/introduces/moves blocks around. Then you really need to keep an eye
on those declarations.

I thought it was supposed to make life easier?

> It only makes sense to declare z in the first branch of the if statement
> if z is only used in that branch and nowhere else.

As I'd understood it (up to now anyway), you could turn the first assignment
to a variable, into a declaration.

>> }
>>
>> printf("X,Y,Z = %d %d %d\n", x, y, z);
>> }
>>
>> 'z' is declared on it's first use, but because that happens inside a pair
>> of
>> braces, then it's scope is limited to that block.
>>
>> In that case, the problems are worse than I thought; if someone first
>> writes:
>>
>>  if (x)
>>   int z=3;
>
> This is not valid C; the grammar for an if statement is
>
>  if (expression) statement

The following code compiles and works under Digital Mars' compiler:

void fn(void){
int x=1,y=2;

if (x)
 int z=3;
else {
 z=4;
}

printf("X,Y,Z = %d %d %d\n", x, y, z);
}

with a subsequent error after 'int z=3' is enclosed in braces.

> The situation that you describe can not occur. The brace-enclosed block
> has to be there in the first place.

Maybe that's another DMC bug. I couldn't reproduce it with other compilers,
but that might have been them rejecting such declarations anyway.

In any case, it does highlight some issues when trying to declare variables
at first use; it's not always possible, or introduces restrictions on use.

-- 
Bartc

Thread

What a stupid gcc! zgene <nospam@nospam.com> - 2012-06-13 21:41 +0000
  Re: What a stupid gcc! James Kuyper <jameskuyper@verizon.net> - 2012-06-13 18:01 -0400
    Re: What a stupid gcc! Noob <root@127.0.0.1> - 2012-06-14 13:00 +0200
      Re: What a stupid gcc! Nomen Nescio <nobody@dizum.com> - 2012-06-14 14:33 +0200
        Re: What a stupid gcc! Rui Maciel <rui.maciel@gmail.com> - 2012-06-14 14:46 +0100
        Re: What a stupid gcc! Noob <root@127.0.0.1> - 2012-06-14 18:19 +0200
  Re: What a stupid gcc! Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-06-13 18:06 -0400
  Re: What a stupid gcc! jt@toerring.de (Jens Thoms Toerring) - 2012-06-13 22:19 +0000
    Re: What a stupid gcc! Rui Maciel <rui.maciel@gmail.com> - 2012-06-14 09:47 +0100
      Re: What a stupid gcc! Rui Maciel <rui.maciel@gmail.com> - 2012-06-14 14:37 +0100
  Re: What a stupid gcc! Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2012-06-13 17:05 -0600
  Re: What a stupid gcc! Nick Bowler <nbowler@draconx.ca> - 2012-06-14 00:09 +0000
  Re: What a stupid gcc! Varun Tewari <tewari.varun@gmail.com> - 2012-06-14 03:14 -0700
    Re: What a stupid gcc! James Kuyper <jameskuyper@verizon.net> - 2012-06-14 06:56 -0400
    Re: What a stupid gcc! Jorgen Grahn <grahn+nntp@snipabacken.se> - 2012-06-17 07:18 +0000
      Re: What a stupid gcc! "BartC" <bc@freeuk.com> - 2012-06-17 11:47 +0100
        Re: What a stupid gcc! James Kuyper <jameskuyper@verizon.net> - 2012-06-17 09:31 -0400
          Re: What a stupid gcc! "BartC" <bc@freeuk.com> - 2012-06-18 12:34 +0100
            Re: What a stupid gcc! James Kuyper <jameskuyper@verizon.net> - 2012-06-18 08:18 -0400
              Re: What a stupid gcc! gwowen <gwowen@gmail.com> - 2012-06-18 05:42 -0700
                Re: What a stupid gcc! James Kuyper <jameskuyper@verizon.net> - 2012-06-18 09:39 -0400
              Re: What a stupid gcc! Rich Webb <bbew.ar@mapson.nozirev.ten> - 2012-06-18 09:06 -0400
                Re: What a stupid gcc! ImpalerCore <jadill33@gmail.com> - 2012-06-18 07:18 -0700
            Re: What a stupid gcc! nick_keighley_nospam@hotmail.com - 2012-06-19 00:13 -0700
              Re: What a stupid gcc! "BartC" <bc@freeuk.com> - 2012-06-19 11:28 +0100
                Re: What a stupid gcc! James Kuyper <jameskuyper@verizon.net> - 2012-06-19 07:30 -0400
                Re: What a stupid gcc! nick_keighley_nospam@hotmail.com - 2012-06-20 00:16 -0700
        Re: What a stupid gcc! Rui Maciel <rui.maciel@gmail.com> - 2012-06-17 15:52 +0100
        Re: What a stupid gcc! Noob <root@localhost> - 2012-06-18 09:07 +0200
        Re: What a stupid gcc! Jorgen Grahn <grahn+nntp@snipabacken.se> - 2012-06-18 09:03 +0000
        Re: What a stupid gcc! Andrew Smallshaw <andrews@sdf.lonestar.org> - 2012-06-18 16:02 +0000
          Re: What a stupid gcc! "BartC" <bc@freeuk.com> - 2012-06-18 19:40 +0100
            Re: What a stupid gcc! Noob <root@localhost> - 2012-06-18 23:52 +0200
            Re: What a stupid gcc! Ike Naar <ike@iceland.freeshell.org> - 2012-06-18 23:09 +0000
              Re: What a stupid gcc! "BartC" <bc@freeuk.com> - 2012-06-19 01:30 +0100
                Re: What a stupid gcc! Ian Collins <ian-news@hotmail.com> - 2012-06-19 13:03 +1200
                Re: What a stupid gcc! James Kuyper <jameskuyper@verizon.net> - 2012-06-19 06:34 -0400
                Re: What a stupid gcc! Ike Naar <ike@sverige.freeshell.org> - 2012-06-19 08:43 +0000
                Re: What a stupid gcc! "BartC" <bc@freeuk.com> - 2012-06-19 11:00 +0100
                Re: What a stupid gcc! James Kuyper <jameskuyper@verizon.net> - 2012-06-19 07:05 -0400
                Re: What a stupid gcc! Ian Collins <ian-news@hotmail.com> - 2012-06-19 23:21 +1200
                Re: What a stupid gcc! Ian Collins <ian-news@hotmail.com> - 2012-06-19 23:22 +1200
                Re: What a stupid gcc! Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-06-19 13:45 +0100
                Re: What a stupid gcc! "BartC" <bc@freeuk.com> - 2012-06-19 15:23 +0100
                Re: What a stupid gcc! Ike Naar <ike@iceland.freeshell.org> - 2012-06-19 16:14 +0000
                Re: What a stupid gcc! "BartC" <bc@freeuk.com> - 2012-06-19 18:01 +0100
                Re: What a stupid gcc! James Kuyper <jameskuyper@verizon.net> - 2012-06-19 13:59 -0400
                Re: What a stupid gcc! Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2012-06-19 15:29 -0600
                Re: What a stupid gcc! Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-06-19 18:22 +0100
                Re: What a stupid gcc! "BartC" <bc@freeuk.com> - 2012-06-19 21:13 +0100
                Re: What a stupid gcc! Lew Pitcher <lpitcher@teksavvy.com> - 2012-06-19 16:27 -0400
                Re: What a stupid gcc! James Kuyper <jameskuyper@verizon.net> - 2012-06-19 16:38 -0400
                Re: What a stupid gcc! Kenneth Brody <kenbrody@spamcop.net> - 2012-06-20 09:47 -0400
                Re: What a stupid gcc! Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-06-19 22:44 +0100
                Re: What a stupid gcc! nick_keighley_nospam@hotmail.com - 2012-06-21 01:39 -0700
                Re: What a stupid gcc! "BartC" <bc@freeuk.com> - 2012-06-21 10:55 +0100
                Re: What a stupid gcc! nick_keighley_nospam@hotmail.com - 2012-06-21 04:11 -0700
                Re: What a stupid gcc! "BartC" <bc@freeuk.com> - 2012-06-21 12:36 +0100
                Re: What a stupid gcc! David Brown <david@westcontrol.removethisbit.com> - 2012-06-21 15:33 +0200
                Re: What a stupid gcc! Andrew Smallshaw <andrews@sdf.lonestar.org> - 2012-06-21 14:15 +0000
                Re: What a stupid gcc! Kenneth Brody <kenbrody@spamcop.net> - 2012-06-20 09:37 -0400
                Re: What a stupid gcc! "BartC" <bc@freeuk.com> - 2012-06-20 14:54 +0100
                Re: What a stupid gcc! Kenneth Brody <kenbrody@spamcop.net> - 2012-06-20 18:19 -0400
                Re: What a stupid gcc! "BartC" <bc@freeuk.com> - 2012-06-21 00:13 +0100
                Re: What a stupid gcc! Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-06-21 02:09 +0100
                Re: What a stupid gcc! nick_keighley_nospam@hotmail.com - 2012-06-21 02:05 -0700
                Re: What a stupid gcc! "BartC" <bc@freeuk.com> - 2012-06-21 11:49 +0100
                Re: What a stupid gcc! Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-06-21 14:24 +0100
                Re: What a stupid gcc! nick_keighley_nospam@hotmail.com - 2012-06-22 00:38 -0700
                Re: What a stupid gcc! Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-06-22 13:37 +0100
                Re: What a stupid gcc! nick_keighley_nospam@hotmail.com - 2012-06-21 01:57 -0700
                Re: What a stupid gcc! "BartC" <bc@freeuk.com> - 2012-06-21 11:46 +0100
                Re: What a stupid gcc! Kenneth Brody <kenbrody@spamcop.net> - 2012-06-21 14:37 -0400
                Re: What a stupid gcc! Andrew Smallshaw <andrews@sdf.lonestar.org> - 2012-06-21 19:38 +0000
                Re: What a stupid gcc! nick_keighley_nospam@hotmail.com - 2012-06-21 01:41 -0700
                Re: What a stupid gcc! Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-06-21 12:28 +0100
              Re: What a stupid gcc! Kaz Kylheku <kaz@kylheku.com> - 2012-06-19 15:05 +0000
        Re: What a stupid gcc! Ian Collins <ian-news@hotmail.com> - 2012-06-19 09:37 +1200
          Re: What a stupid gcc! ImpalerCore <jadill33@gmail.com> - 2012-06-18 15:18 -0700
          Re: What a stupid gcc! Paul J Gans <gansno@panix.com> - 2012-06-18 23:21 +0000
            Re: What a stupid gcc! Ian Collins <ian-news@hotmail.com> - 2012-06-19 11:26 +1200
              Re: What a stupid gcc! Paul J Gans <gansno@panix.com> - 2012-06-19 01:46 +0000
                Re: What a stupid gcc! James Kuyper <jameskuyper@verizon.net> - 2012-06-19 07:19 -0400
                Re: What a stupid gcc! Stephen Sprunk <stephen@sprunk.org> - 2012-06-19 08:01 -0500
                Re: What a stupid gcc! James Kuyper <jameskuyper@verizon.net> - 2012-06-19 09:25 -0400
                Re: What a stupid gcc! Les Cargill <lcargill99@comcast.com> - 2012-06-19 12:57 -0500
                Re: What a stupid gcc! James Kuyper <jameskuyper@verizon.net> - 2012-06-19 14:59 -0400
            Re: What a stupid gcc! Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-06-19 01:36 +0100
              Re: What a stupid gcc! Paul J Gans <gansno@panix.com> - 2012-06-19 01:48 +0000
          Re: What a stupid gcc! Les Cargill <lcargill99@comcast.com> - 2012-06-18 19:50 -0500
          Re: What a stupid gcc! nick_keighley_nospam@hotmail.com - 2012-06-19 00:19 -0700
            Re: What a stupid gcc! Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-06-19 12:56 +0100
              Re: What a stupid gcc! nick_keighley_nospam@hotmail.com - 2012-06-20 00:26 -0700
                Re: What a stupid gcc! James Kuyper <jameskuyper@verizon.net> - 2012-06-20 06:31 -0400
      Re: What a stupid gcc! Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2012-06-18 00:18 -0600
        Re: What a stupid gcc! Jorgen Grahn <grahn+nntp@snipabacken.se> - 2012-06-18 09:15 +0000
  Re: What a stupid gcc! Kaz Kylheku <kaz@kylheku.com> - 2012-06-14 23:21 +0000

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