Breaking out of a nested loop

The Comet · 2016-07-18T21:55:55

I'm a little disappointed to say the least that breaking from a nested loop feels this dirty in C/C++. It's not an uncommon occurrence, and yet, the "cleanest" solution we have is to use a label and a goto statement. (Obligatory xkcd joke) In C/C++ the "cleanest" code for breaking from an inner loop: int i, j; for(i = 0; i < 10; i++) { for(j = 0; j < 10; j++) { if(i - 1 == j + 1) goto outer; } } outer: I feel like we need a new keyword. Perhaps a break_harder or combo_break keyword to break from 2 loops or something? Turns out PHP has this feature. In PHP: <?php for($i = 0; $i < 10; $i++) { for($j = 0; $j < 10; $j++) { if($i - 1 == $j + 1) break 2; } } ?> In Java you can use named blocks to achieve the same result: outer: { for(int i = 0; i < 10; i++) { for(int j = 0; j < 10; j++) { if(i - 1 == j + 1) break outer; } } } How do you guys do this in C/C++? Do you think having a break statement like in PHP would be beneficial in C/C++? People have told me to extract the loops into a separate static function and use return instead of a goto. Do you think this is better practice?

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Started by TheComet July 25, 2015 06:13 PM

50 comments, last by ExErvus 7 years, 9 months ago

owiley

257

May 27, 2016 08:59 PM

Just replace the for loops with if goto pairs so that goto won't look so lonely.

So...
int i = 0, j = 0;
    loop:
        if(i - 1 == j + 1)
            goto outer;
    ++j;
    if(j < 10)
        goto loop;
    ++i;
    if(i < 10)
        goto loop;

outer:
Seems pretty clean to me!

you have to set j back to zero tho else it does the job. Also this is how assembly would work

Bring more Pain

MarkS_

3,509

May 27, 2016 10:24 PM

you have to set j back to zero tho else it does the job. Also this is how assembly would work

Oh crap! :unsure:

ExErvus

696

July 18, 2016 09:55 PM

So... int i = 0, j = 0; loop: if(i - 1 == j + 1) goto outer; ++j; if(j < 10) goto loop; j = 0; ++i; if(i < 10) goto loop; outer: Seems pretty clean to me!

That looks terrifying

Breaking out of a nested loop

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