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By accident I came across a bug like this in some Linux code I'd
written today. All that had happened is I forgot the "else" yet the
code still compiled and ran. A simplified example is below.

#include <stdio.h>

main()
{
int a;
if (1 == 1) a = 1;
{
a = 2;
}
printf("a = %d\n",a);
}

When run it will print "a = 2". Should it compile at all or is GCCs
parser broken?

B2003

In article <a28f28eb-52b0-4fd3-b045->,
Boltar <> wrote:
>By accident I came across a bug like this in some Linux code I'd
>written today. All that had happened is I forgot the "else" yet the
>code still compiled and ran. A simplified example is below.
>
>#include <stdio.h>
>
>main()
>{
> int a;
> if (1 == 1) a = 1;
> {
> a = 2;
> }
> printf("a = %d\n",a);
>}
>
>When run it will print "a = 2". Should it compile at all or is GCCs
>parser broken?
>
>B2003

Time for me to re-post my "I wrote this hello, world program and it
compiled and ran just fine; why?" post.

On 27 Feb, 09:44, gaze...@xmission.xmission.com (Kenny McCormack)
wrote:
> Time for me to re-post my "I wrote this hello, world program and it
> compiled and ran just fine; why?" post.

I should've known better than to expect a sensible answer from this
group.

Anyway , I just realised its treating the bracketed part as a seperate
block so you can save anymore sarcastic responses.

B2003

Boltar wrote:
> By accident I came across a bug like this in some Linux code I'd
> written today. All that had happened is I forgot the "else" yet the
> code still compiled and ran. A simplified example is below.
>
> #include <stdio.h>
>
> main()
> {
> int a;
> if (1 == 1) a = 1;
here you assign 1 to a, always, as 1 always equals 1

> {
> a = 2;
here you assign 2 to a, always

> }
> printf("a = %d\n",a);
> }
>
> When run it will print "a = 2". Should it compile at all or is GCCs
> parser broken?
Why do you think it is broken or should print something else?

Bye, Jojo

Boltar <> writes:

> By accident I came across a bug like this in some Linux code I'd
> written today. All that had happened is I forgot the "else" yet the
> code still compiled and ran. A simplified example is below.
>
> #include <stdio.h>
>
> main()
> {
> int a;
> if (1 == 1) a = 1;
> {
> a = 2;
> }
> printf("a = %d\n",a);
> }
>
> When run it will print "a = 2". Should it compile at all or is GCCs
> parser broken?

It is entirely legal. A compound statement (braces containing other
statements) is just another valid option where a statement is
required.

--
Ben.

Boltar said:

> By accident I came across a bug like this in some Linux code I'd
> written today. All that had happened is I forgot the "else" yet the
> code still compiled and ran. A simplified example is below.
>
> #include <stdio.h>
>
> main()
> {
> int a;
> if (1 == 1) a = 1;
> {
> a = 2;
> }
> printf("a = %d\n",a);
> }
>
> When run it will print "a = 2". Should it compile at all or is GCCs
> parser broken?

It's legal.

{
a = 2;
}

is a compound statement. You can have these pretty much anywhere you can
have an ordinary statement. If you like, you can do this:

#include <stdio.h>
int main(void)
{
{ printf("Hello, world!\n"); }
{ puts("How are you today?"); }
{ puts("Earthquake in UK - film at 11"); }
{ return 0; }
}

Although the above is a pastiche, this facility is nevertheless useful and
powerful, but does have the unfortunate consequence you have noted -
forgetting an "else" doesn't necessarily give you the syntax error you'd
have hoped for!

--
Richard Heathfield <http://www.cpax.org.uk>
Email: -http://www. +rjh@
Google users: <http://www.cpax.org.uk/prg/writings/googly.php>
"Usenet is a strange place" - dmr 29 July 1999

Boltar said:

> On 27 Feb, 09:44, gaze...@xmission.xmission.com (Kenny McCormack)
> wrote:
>> Time for me to re-post my "I wrote this hello, world program and it
>> compiled and ran just fine; why?" post.
>
> I should've known better than to expect a sensible answer from this
> group.

Mr McCormack is a troll. You get them in any group.

I have already posted a sensible answer.

--
Richard Heathfield <http://www.cpax.org.uk>
Email: -http://www. +rjh@
Google users: <http://www.cpax.org.uk/prg/writings/googly.php>
"Usenet is a strange place" - dmr 29 July 1999

Boltar wrote:

> By accident I came across a bug like this in some Linux code I'd
> written today. All that had happened is I forgot the "else" yet the
> code still compiled and ran. A simplified example is below.
>
> #include <stdio.h>
>
> main()
> {
> int a;
> if (1 == 1) a = 1;
> {
> a = 2;
> }
> printf("a = %d\n",a);
> }
>
> When run it will print "a = 2". Should it compile at all or is GCCs
> parser broken?

No this is legal C. A opening { starts a compound statement or block,
closed by the next }. It's sometimes useful for data confinement.

<OT>
There *is* a related GCC extension which allows a compound statement
enclosed in parenthesis as an expression, but this is not an
illustration of one. This is pure Standard C.
</OT>

In article <a28f28eb-52b0-4fd3-b045->,
Boltar <> wrote:
>By accident I came across a bug like this in some Linux code I'd

>main()
>{
> int a;
> if (1 == 1) a = 1;
> {
> a = 2;
> }
> printf("a = %d\n",a);
>}

Perhaps you should run it through an indenting tool for enlightenment:

main()
{
int a;

if (1 == 1)
a = 1;

{
a = 2;
}

printf("a = %d\n",a);
}

-- Richard
--
:wq

Richard Heathfield wrote:
>
> Boltar said:
>
> > By accident I came across a bug like this in some Linux code I'd
> > written today. All that had happened is I forgot the "else" yet the
> > code still compiled and ran. A simplified example is below.
> >
> > #include <stdio.h>
> >
> > main()
> > {
> > int a;
> > if (1 == 1) a = 1;
> > {
> > a = 2;
> > }
> > printf("a = %d\n",a);
> > }
> >
> > When run it will print "a = 2". Should it compile at all or is GCCs
> > parser broken?
>
> It's legal.
>
> {
> a = 2;
> }
>
> is a compound statement. You can have these pretty much anywhere you can
> have an ordinary statement. If you like, you can do this:
>
> #include <stdio.h>
> int main(void)
> {
> { printf("Hello, world!\n"); }
> { puts("How are you today?"); }
> { puts("Earthquake in UK - film at 11"); }
> { return 0; }
> }
>
> Although the above is a pastiche, this facility is nevertheless useful and
> powerful, but does have the unfortunate consequence you have noted -
> forgetting an "else" doesn't necessarily give you the syntax error you'd
> have hoped for!

In case the OP (or anyone else) is wondering where this would be
useful, consider:

#if ENABLE_SOME_FEATURE
if ( new_feature_is_enabled() )
{
do_it_the_new_way();
do_another_thing_the_new_way();
}
else
#endif
{
do_it_the_old_way();
do_the_other_thing_the_old_way();
}

Compare this "clean" version to how you would have to write it if
compound statements weren't legal on their own.

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