Array Initialization

[Joona I Palaste]

Re: Array Initialization

Jeff <nothing@notexi st.com> scribbled the following:[color=blue]
> "Brett Frankenberger" <rbf@panix.co m> wrote in message
> news:bj3h6s$gi6 $1@reader2.pani x.com...[color=green]
>> In article <20030902214254 .22819.00000248 @mb-m23.aol.com>,
>> Bigdakine <bigdakine@aol. comGetaGrip> wrote:[color=darkred]
>> >
>> >Heck, I'm interested to know how this even compiled.
>> > (void)printf("% d ", array[x,y]);[/color]
>>
>> Why wouldn't it? 'x,y' is a perfectly valid expression (equivalent to
>> 'y'), and array[y] doesn't violate any constraints (and would even be
>> useful, defined behavior under some circumstances), so one wouldn't
>> expect compilation to fail. Of course, array[y] is type (pointer to
>> int), so attempting to print it with "%d" is undefined behavior.[/color][/color]
[color=blue]
> Yes, it can be compiled. The comma between a and b is "comma operator".
> The expression "a,b" will return "b" silently. You can even write[/color]
[color=blue]
> array[ printf("Hello man") , y][/color]
[color=blue]
> To OP :
> It dosen't mean "array[x,y] " is the correct syntax for accessing
> two-dimensional
> array. You should write "array[x][y]".[/color]

However, due to C's wacky ways of working, the following code is
perfectly legal:

#include <stdio.h>
int main(void) {
int array[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 };
printf("%d\n", array[printf("Hello man\n")]);
return 0;
}

This should print out:
Hello man
11

Because "Hello man\n" is 10 printable characters (and a '\0'), and
array[10] is 11.

--
/-- Joona Palaste (palaste@cc.hel sinki.fi) ---------------------------\
| Kingpriest of "The Flying Lemon Tree" G++ FR FW+ M- #108 D+ ADA N+++|
| http://www.helsinki.fi/~palaste W++ B OP+ |
\----------------------------------------- Finland rules! ------------/
"And according to Occam's Toothbrush, we only need to optimise the most frequent
instructions."
- Teemu Kerola

[Martien Verbruggen]

Re: Array Initialization

On Tue, 2 Sep 2003 23:10:21 -0400,
Henry <henryhc@knolog y.net> wrote:[color=blue]
>
> "Irrwahn Grausewitz" <irrwahn@freene t.de> wrote in message
> news:62jalvco4m t87i4994jbbam95 mi808h42a@4ax.c om...[color=green]
>> "Henry" <henryhc@knolog y.net> wrote in
>> <vlaig9e9eht590 @corp.supernews .com>:
>> <SNIP>[color=darkred]
>> >Ok thanks, when I changed the way it was typed it worked much better..
>> >Strangly the array[x,y] came straight from the "Practical C" book.[/color]
>> If there are more flaws like this in the book, get a better one.
>> (Btw.: were the (void) casts for printf straight from that book, too?[/color]
>
> Yes... it seemed strange to me that they would expect a return on printf[/color]

That's not strange, since printf() does return a value. Explicitly
casting it away like that, however, isn't really necessary. It used to
be done a lot to shut up warnings from lint about discarded return
values, but it isn't necessary to do.

Martien
--
|
Martien Verbruggen | The problem with sharks is that they are too
| large to get to the shallow end of the gene
| pool. -- Scott R. Godin

[Jens.Toerring@physik.fu-berlin.de]

Re: Array Initialization

Henry <henryhc@knolog y.net> wrote:[color=blue][color=green][color=darkred]
>> > Ok thanks, when I changed the way it was typed it worked much better..
>> > Strangly the array[x,y] came straight from the "Practical C" book.[/color]
>>
>> Burn your book :-)[/color][/color]
[color=blue]
> Well I started learning C using the K&R book but it assumed too much, so I
> was told "Practical C" would be a much better book to go through because it
> would be more in depth and would cover topics that K&R would seemingly skip
> over. So far "PC" has been compeltly different.. using commands such as
> scanf and fgets which K&R didn't even mention[/color]

You better have a another look at your K&R2 (I hope you have the second
edition), and go to section 7.4 (completely devoted to scanf()) and 7.7
(discusses fgets() and fputs()). K&R probably doesn't introduce these
functions earlier because you need to have understood about pointers
and arrays before you can use them. I guess that a lot of the questions
you see asked in clc why stuff like

char *my_string;
double my_float;
scanf( "%f %s", my_float, my_string );

does not work may be due to books introducing scanf() too early...

Regards, Jens
--
_ _____ _____
| ||_ _||_ _| Jens.Toerring@p hysik.fu-berlin.de
_ | | | | | |
| |_| | | | | | http://www.physik.fu-berlin.de/~toerring
\___/ens|_|homs|_|oe rring

[Irrwahn Grausewitz]

Re: Array Initialization

"Henry" <henryhc@knolog y.net> wrote in
<vlamrim0cu7ec3 @corp.supernews .com>:
[color=blue][color=green][color=darkred]
>> > Ok thanks, when I changed the way it was typed it worked much better..
>> > Strangly the array[x,y] came straight from the "Practical C" book.[/color]
>>
>> Burn your book :-)
>>
>> [snip]
>>
>> --
>> Jeff[/color]
>
>LOL
>
>Well I started learning C using the K&R book but it assumed too much, so I
>was told "Practical C" would be a much better book to go through because it
>would be more in depth and would cover topics that K&R would seemingly skip
>over. So far "PC" has been compeltly different.. using commands such as
>scanf and fgets which K&R didn't even mention[/color]

Huh? You must own a very rare preliminary version of K&R! :)

In my copy of K&R2 fgets and (f)scanf are used frequently in
the examples. scanf has a section dedicated to it as well:
Chapter 7.4: Formatted Input - Scanf
And in 7.7 the source code for a possible fgets/fputs
implementation is given...


--
No sig today.

[Stuart]

Re: Array Initialization

rbf@panix.com (Brett Frankenberger) wrote in message news:<bj3h6s$gi 6$1@reader2.pan ix.com>...[color=blue]
> In article <20030902214254 .22819.00000248 @mb-m23.aol.com>,
> Bigdakine <bigdakine@aol. comGetaGrip> wrote:[color=green]
> >
> >Heck, I'm interested to know how this even compiled.
> > (void)printf("% d ", array[x,y]);[/color]
>
> Why wouldn't it? 'x,y' is a perfectly valid expression (equivalent to
> 'y'), and array[y] doesn't violate any constraints (and would even be
> useful, defined behavior under some circumstances), so one wouldn't
> expect compilation to fail. Of course, array[y] is type (pointer to
> int), so attempting to print it with "%d" is undefined behavior.
>
> -- Brett[/color]

I forgot about the "," operator.

Thanx. Be that as it may, if the intent is to print an element of a
2-d array, it should be written as [x][y]

Stuart