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| From | James Kuyper <jameskuyper@verizon.net> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: What a stupid gcc! |
| Date | 2012-06-19 13:59 -0400 |
| Organization | A noiseless patient Spider |
| Message-ID | <4FE0BDEE.4000301@verizon.net> (permalink) |
| References | (9 earlier) <jrpino$1lj$1@dont-email.me> <0.0ff9867a492014af7e6b.20120619134530BST.87395rsc5x.fsf@bsb.me.uk> <jrq23v$rtv$1@dont-email.me> <slrn3vfsju19bv.j4j.ike@iceland.freeshell.org> <jrqb9i$oop$1@dont-email.me> |
On 06/19/2012 01:01 PM, BartC wrote:
> "Ike Naar" <ike@iceland.freeshell.org> wrote in message
> news:slrn3vfsju19bv.j4j.ike@iceland.freeshell.org...
...
>> 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.
You can, anywhere a declaration is permitted, but only if such a
declaration gives the variable's name sufficient scope to cover all
subsequent uses.
Declarations are permitted at file scope and as elements of blocks, but
there are a number of places in the grammar where a statement is
permitted, but a declaration is not: all declarations of x in following
lines are syntax errors:
label: int x=0;
if(i==3) int x=0;
else double x = 0;
while(a>3) int x = a--;
do int x = a++;
while(a < 100);
for(int i=0; i<100; i++) int x = i;
switch(a) int x=a;
switch(b)
{
case 25: int x = a;
break;
default: int x = b;
}
Every one of those cases can be dealt with by enclosing the declaration
in a block; in which case it would have a scope restricted to that
block. That would be pretty pointless unless that same block also
contained at least one statement that actually uses the variable.
...
> 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.
Then it's not a conforming C compiler. There are only two C grammar
productions for an if statement, and that code doesn't fit either one:
if ( expression ) statement
if ( expression ) statement else statement
"int z=3;" is a declaration, not a statement. C++ has a concept of a
declaration-statement, which does not exist in C, so
if (x)
int z=3;
is permitted, but the C standard defines it as equivalent of
if (x)
{
int z=3;
}
so we can't explain DMC's behavior by assuming that it follows C++ rules.
Such a declaration would be pretty pointless in C, even if it were
allowed. However, in C++, if z had a type with a non-trivial constructor
or a non-trivial destructor, such a declaration could actually make sense.
...
> 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.
That's true, and well understood. Declaring variables at first use is
only possible when first use occurs at a location that would give the
variable sufficient scope to cover all subsequent uses. This is often
possible, but not always.
Back to comp.lang.c | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll 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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