is there any array[a,b] syntax in c?

Question

while reading about the c preprocessor I got something like array[x=y,x+1]. I haven't seen this kind of syntax in c before and after searching for many hours I didn't find anything useful.

#include <stdio.h>

int main() {
    int arr[] = {5,10,15};
    printf("%d %d %d",arr[0,1]);
    return 0;
}

outputs: 10 1762365112 1769491896

Can someone elaborate on this?

https://en.cppreference.com/w/c/language/operator_other#Comma_operator — Pignotto, Jan 27 '23 at 08:17
`printf("%d %d %d",arr[0,1]);` Welcome to SO. Don't you get some warning from your compiler that you don't have enough parameters for these 3 format specifiers? Using `%d` without any parameter is causing undefined behaviour. — Gerhardh, Jan 27 '23 at 08:18
@DevSolar Sounds like the well-known code quality metric [WTFs/minute](https://i0.wp.com/commadot.com/wp-content/uploads/2009/02/wtf.png?resize=550%2C433) — Lundin, Jan 27 '23 at 08:34
@Jabberwocky I was unaware of the comma operator, so I was just checking if `array[0,1]` returns the elements from 0 and 1 index...but it was printing the element with the last specified index and two garbage values with no error. — coco, Jan 27 '23 at 14:18
What compiler are you using? How cou you compile? You should increase warning level. For GCC or CLang you can use `-Wall -Wextra -pedantic` — Gerhardh, Jan 27 '23 at 14:21
Alas, not in C, but in `C++` you could... muah hah hah hah... (Don’t though.) — Dúthomhas, Jan 27 '23 at 22:12

score 2 · Accepted Answer · answered Jan 27 '23 at 08:23

Because of how the comma operator (,) works in C, the effect of the (questionable and woefully hard to read) array[x=y,x+1] is to first copy the value of y into x and then use x+1 as the normal (single dimensional, non-ranged, or whatever you were expecting) index in to the array.

(I do not see the need to discuss your experimental code.)

See the link to documentation of comma operator, as kindly provided in comments by Pignotto:
https://en.cppreference.com/w/c/language/operator_other#Comma_operator

thanks @Yunnosch and everyone else for clearing it out! – coco Jan 27 '23 at 14:21 — coco, Jan 27 '23 at 14:21

is there any array[a,b] syntax in c?

1 Answers1