Comment On A Common C Dilemma

Ahh you youngsters probably don't remember the for-while loop. The good olde days.

This code ain't for no boundary overrun prevention, nossir! It's actually a very clever, ingenious, way to add a NOP on the program, so that the snipped become 32bit-aligned!

I always use these when I only want my code to run for a while.

It took me a few moments to understand the "Gordon's c/w came up w/ this".

It's too long this way! Just take away some vowels, nobody will notice. :-)

I once wrote this for loop:

for (byte b = 0; b <= 255; b++) {

// code

}

Re:José Rodrigues

a good compiler would optimize that instruction out

SlyEcho:

I once wrote this for loop:

for (byte b = 0; b <= 255; b++) {

// code

}

I haven't used C for a while so I had to think for a second. That's nice.

"a good compiler would optimize that instruction out"

A bad programmer would forget to use the good compiler's optimization flags.

You remembered that only fools assume bytes are 8 bits?

while (1); or any other number probably didn't work, but 0 appeared to correct the problem.

noob question: the byte is signed, right?

tldr

ledhund:

noob question: the byte is signed, right?

It's probably not signed. But it is always going to be less than or equal to 255. Since the range of values is 0~255

Heh, I had a boundary overflow problem once or twice with Delphi code.

I wrote this apparently simple snippet of code:

for i:=start to end do
// code

which however appeared to freeze everything, as if start > end when the loop is started it will apparently run forever...or for very long, depending on what i is (an Integer however will take pretty long...). Why? Because Delphi implies only a precise equality as the loop ending condition. No "greater or equal" here. The solution was to either replace the for loop with a "while (condition) do" construct, or explicitly checking for the start>end condition before the if.

What are you doing?
Rdng TDWTF n lol @ code

ledhund:

noob question: the byte is signed, right?

Thinking here. I never did do C, but I did teach C++ once on TV.

The byte is NOT signed, but it will overflow (the b++ overflows the byte), so it should go to 0. Infinite loop.

Nice.
Jim.

jimlangrunner:

ledhund:

noob question: the byte is signed, right?

Thinking here. I never did do C, but I did teach C++ once on TV.

The byte is NOT signed, but it will overflow (the b++ overflows the byte), so it should go to 0. Infinite loop.

Nice.
Jim.

doh! I didn't read the = so imagined the overflow already at 127++

Flanged Magnet:

You remembered that only fools assume bytes are 8 bits?

Also old farts like me. But then it's not an exclusive or.

tl;dr

Kiss me I'm Polish:

It took me a few moments to understand the "Gordon's c/w came up w/ this".

I'm scared that I read and understood it without even realizing they were abbreviated. o_o

I did that once. Took me far too long to figure out why it wouldn't end.

lolwtf:

Kiss me I'm Polish:

It took me a few moments to understand the "Gordon's c/w came up w/ this".

I'm scared that I read and understood it without even realizing they were abbreviated. o_o

Reminds me of this fortune:
[Temperature 13 C][16:28:13 01-April-09][/home/adam]
[adam@owl]$ fortune -m "f u cn"
%% (fortunes)
f u cn rd ths, u cn gt a gd jb n cmptr prgrmmng.

Flanged Magnet:

You remembered that only fools assume bytes are 8 bits?

Don't be silly. Eight bits is a dollar.

SlyEcho:

I once wrote this for loop:

for (byte b = 0; b <= 255; b++) {

// code

}

I once saw this while loop:

int n = 0;

while(n >= 0) n++;

G++ with -O3 turned it into an infinite loop. It's not even a bug.

My favourite is always this one - I keep finding that my finigers typo it!

for(int i=0; i<end; i++); 

{

    // code

}

At first I thought I was looking at a for...while loop. But it turns out the ; substitutes for the body of the while loop, so it's exactly the same as:

for (int i=0;i<max; i++) {

   ...

} 



while(0) {}

Plus this way it works in Java as well as C.

Um, no. While the terminating condition of a for loop is strict equality in Delphi, the runtime also checks that Start <= End. If Start > End, then it will skip the loop altogether. Also, End is only evaluated once for for loops in Delphi (e.g. If End is really a function call, the function is only called once at the first check.). For a while loop, the condition is evaluated for every iteration.

Ergo, checking for Start > End before entering a for loop doesn't do anything unless End is a function call with a side effect, and while loops have subtly different semantics that can make a difference.

the e in olde: extra character!

I call Shenanigans. The

while(0)

was very obviously and poorly Photoshopped in.

It's too long to re-tweet.

Um, no. While the terminating condition of a for loop is strict equality in Delphi, the runtime also checks that Start <= End. If Start > End, then it will skip the loop altogether. Also, End is only evaluated once for for loops in Delphi (e.g. If End is really a function call, the function is only called once at the first check.). For a while loop, the condition is evaluated for every iteration.

Delphi 7, d'oh. And it just froze when ran: debugging the loop revealed that the index variable was merrily stepping its way up to MAXINT and then from -MAXINT...go figure.

Start and End were variables in my case, and I used the default project options. It sure made me go "WTF" when I realized it, and chose the easiest workaround, since I really needed the index variable inside the loop, and felt that increasing them myself just made the whole code look uglier.

Everybody's routing through Twitter now.

One of the nastiest practical jokes I ever read about was how to totally confuse C programmers. To do this, you bury this DEFINE in some ob

scure header file:

#DEFINE do if

I once did this...

    #define EverAndEver ;;

Then you can do...

    for (EverAndEver) {  

        }

A coworker saw it and added the comment:

    for (EverAndEver) {  // Hallelujah, Hallelujah!

        }

Actually, if you count all new lines its 142 characters, and if this was encoded in windows format, its more like 149 characters. There's the real WTF.

Evo:

I once saw this while loop:

int n = 0;

while(n >= 0) n++;

G++ with -O3 turned it into an infinite loop. It's not even a bug.

Hey, it works just as coded. :-)

Random guy:

Evo:

I once saw this while loop:

int n = 0;

while(n >= 0) n++;

G++ with -O3 turned it into an infinite loop. It's not even a bug.

Hey, it works just as coded. :-)

Only on slow machines.

MrEricSir:

while(0) {}

Plus this way it works in Java as well as C.

No. In Java it doesn't. Boolean values in Java are really true or false, not 0 or !0.

If you put a newline before the while(0); it will be immediately obvious what this code does. But when you first look at it, it does make you go "huh".

It is a fair criticism of C/C++ that non-standard indentation can mislead you as to what the code is doing. This code is a good example of that.

Ouch... yet another python fanatic

This was also posted on April 1st but there is no such thing as a for...while construct and they are two separate loops in the code.

This is C++ mate :). Strictly, you can only declare variables in the beginning of a code block / function and not in the head of a for loop (for (int i = 0 ...). Thats wtf :P

pbi:

This is C++ mate :). Strictly, you can only declare variables in the beginning of a code block / function and not in the head of a for loop (for (int i = 0 ...). Thats wtf :P

EDIT: ..Strictly speaking, you can only declare variables ....

ugg boots:

...

And your Captcha was..?

I'm sure the performance boost was amazing too

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