A little bit of C fun...

A little bit of C fun...

[John Carter]

I'm having a little fun going around hurting peoples brains...

Consider for a moment this program excerpt...
   a(&(b){c})

Is this valid C++?

Is this valid C?

What would you need to do to get this to compile?

What does it do?

Could it be tweaked into something useful? (apart from using it to
hurt people's brains with.)



John Carter                             Phone : (64)(3) 358 6639
Tait Electronics                        Fax   : (64)(3) 359 4632
PO Box 1645 Christchurch                Email : john.carter@tait.co.nz
New Zealand

Re: A little bit of C fun...

[me22]

On Wed, Oct 22, 2008 at 00:44, John Carter <john.carter@tait.co.nz> wrote:
>
> Consider for a moment this program excerpt...
>  a(&(b){c})
>
> Is this valid C++?
>
> Is this valid C?
>
> What would you need to do to get this to compile?
>

Use the preprocessor.  Otherwise you can't get braces inside parens.

#define c return 0;
#define b d)
#define a(T) int d; if (T

int main() {
    a(&(b){c})
}

> What does it do?
>

Whatever you want.

> Could it be tweaked into something useful? (apart from using it to
> hurt people's brains with.)
>

No.

Re: A little bit of C fun...

[John Carter]

On Wed, 22 Oct 2008, me22 wrote:

> Use the preprocessor.  Otherwise you can't get braces inside parens.

Nope. I didn't use preprocessor. But warped kudos to you for thinking
of it.

Since you are all struggling, I'll make it easier for you.

I shorten it by one character....
    a(&(b){})

... (but then it does something subtly more that the previous
one...oooh I'm evil!)


John Carter                             Phone : (64)(3) 358 6639
Tait Electronics                        Fax   : (64)(3) 359 4632
PO Box 1645 Christchurch                Email : john.carter@tait.co.nz
New Zealand

RE: A little bit of C fun...

[Austin, Alex]

A guess:
b is a type, and a is a function that takes a pointer to a function that returns b?

-----Original Message-----
From: gcc-help-owner@gcc.gnu.org [mailto:gcc-help-owner@gcc.gnu.org] On Behalf Of John Carter
Sent: Wednesday, October 22, 2008 2:38 PM
To: me22
Cc: gcc-help@gcc.gnu.org
Subject: Re: A little bit of C fun...

On Wed, 22 Oct 2008, me22 wrote:

> Use the preprocessor.  Otherwise you can't get braces inside parens.

Nope. I didn't use preprocessor. But warped kudos to you for thinking
of it.

Since you are all struggling, I'll make it easier for you.

I shorten it by one character....
    a(&(b){})

... (but then it does something subtly more that the previous
one...oooh I'm evil!)


John Carter                             Phone : (64)(3) 358 6639
Tait Electronics                        Fax   : (64)(3) 359 4632
PO Box 1645 Christchurch                Email : john.carter@tait.co.nz
New Zealand

RE: A little bit of C fun...

[Austin, Alex]

Oh, no... I'm dumb.

typedef struct {
        int x;
} b;

int a(b *param)
{
        return printf("%d\n", b->x);
}

int print_number(int c)
{
        return a(&(b){c});
}

-----Original Message-----
From: gcc-help-owner@gcc.gnu.org [mailto:gcc-help-owner@gcc.gnu.org] On Behalf Of Austin, Alex
Sent: Wednesday, October 22, 2008 3:13 PM
To: John Carter; me22
Cc: gcc-help@gcc.gnu.org
Subject: RE: A little bit of C fun...

A guess:
b is a type, and a is a function that takes a pointer to a function that returns b?

-----Original Message-----
From: gcc-help-owner@gcc.gnu.org [mailto:gcc-help-owner@gcc.gnu.org] On Behalf Of John Carter
Sent: Wednesday, October 22, 2008 2:38 PM
To: me22
Cc: gcc-help@gcc.gnu.org
Subject: Re: A little bit of C fun...

On Wed, 22 Oct 2008, me22 wrote:

> Use the preprocessor.  Otherwise you can't get braces inside parens.

Nope. I didn't use preprocessor. But warped kudos to you for thinking
of it.

Since you are all struggling, I'll make it easier for you.

I shorten it by one character....
    a(&(b){})

... (but then it does something subtly more that the previous
one...oooh I'm evil!)


John Carter                             Phone : (64)(3) 358 6639
Tait Electronics                        Fax   : (64)(3) 359 4632
PO Box 1645 Christchurch                Email : john.carter@tait.co.nz
New Zealand

Re: A little bit of C fun...

[me22]

On Wed, Oct 22, 2008 at 15:37, John Carter <john.carter@tait.co.nz> wrote:
> On Wed, 22 Oct 2008, me22 wrote:
>
>> Use the preprocessor.  Otherwise you can't get braces inside parens.
>
> Nope. I didn't use preprocessor. But warped kudos to you for thinking
> of it.
>

Say, what about -std=gnu++0x?  Then the braces can be an initializer list...

Re: A little bit of C fun...

[John Carter]

On Wed, 22 Oct 2008, me22 wrote:

> On Wed, Oct 22, 2008 at 15:37, John Carter <john.carter@tait.co.nz> wrote:
>> On Wed, 22 Oct 2008, me22 wrote:
>>
>>> Use the preprocessor.  Otherwise you can't get braces inside parens.
>>
>> Nope. I didn't use preprocessor. But warped kudos to you for thinking
>> of it.
>>
>
> Say, what about -std=gnu++0x?  Then the braces can be an initializer list...
>

I compiled this with gcc 3 and gcc 4 using -std=c89 and -std=c99 with
-Wall and -W.

gcc-2.95 failed
   a(&(b){c}) 
but passed
   a((b){c})


-W warns about a(&(b){}) but that is one of those cases where -W
  warns about a potential omission in a legal operation.

And yes, you're on the right track now, the braces are an initializer list.



John Carter                             Phone : (64)(3) 358 6639
Tait Electronics                        Fax   : (64)(3) 359 4632
PO Box 1645 Christchurch                Email : john.carter@tait.co.nz
New Zealand

Re: A little bit of C fun...

[John Carter]

On Thu, 23 Oct 2008, John Carter wrote:

> I compiled this with gcc 3 and gcc 4 using -std=c89 and -std=c99 with
> -Wall and -W.
> -W warns about a(&(b){}) but that is one of those cases where -W
> warns about a potential omission in a legal operation.

Ah. I forgot to say -pedantic with the -std=

If I say -pedantic gcc only accepts this stuff for -std=c99 and
doesn't accept the {} empty initializer. (Not that it matters, in that
something still interesting occurs with the {c} version if it contains
more than one field.)



John Carter                             Phone : (64)(3) 358 6639
Tait Electronics                        Fax   : (64)(3) 359 4632
PO Box 1645 Christchurch                Email : john.carter@tait.co.nz
New Zealand

code snippet

[sagrav]

I need a C code snippet to display a *.html file in the web browser. 

Help will be appreciated,

thanks in advance.

Re: code snippet

[Sven Eschenberg]

Wrong list!

This is a gcc specific help list - you might want to try something like 
a general purpose C help list.

-Sven


sagrav schrieb:
> I need a C code snippet to display a *.html file in the web browser.
> Help will be appreciated,
>
> thanks in advance.

RE: A little bit of C fun...

[John Carter]

On Wed, 22 Oct 2008, Austin, Alex wrote:

> b is a type, and a is a function that takes a pointer to a function
> that returns b?

b is a type.
a is a function that takes a pointer to...

So far so good. Nearly, but not quite, keep trying.


John Carter                             Phone : (64)(3) 358 6639
Tait Electronics                        Fax   : (64)(3) 359 4632
PO Box 1645 Christchurch                Email : john.carter@tait.co.nz
New Zealand

RE: A little bit of C fun...

[John Carter]

On Wed, 22 Oct 2008, Austin, Alex wrote:

> Oh, no... I'm dumb.
>
> typedef struct {
>        int x;
> } b;
>
> int a(b *param)
> {
>        return printf("%d\n", b->x);
> }
>
> int print_number(int c)
> {
>        return a(&(b){c});
> }

Great! You've got it!

Now for extra credit...

Where would this trick be sort of useful?

> I shorten it by one character....
>    a(&(b){})
>
> ... (but then it does something subtly more that the previous
> one...oooh I'm evil!)

What would your program print if you took out the c and why?

int print_number(void)
{
        return a(&(b){});
}




John Carter                             Phone : (64)(3) 358 6639
Tait Electronics                        Fax   : (64)(3) 359 4632
PO Box 1645 Christchurch                Email : john.carter@tait.co.nz
New Zealand