"Warning: Comma within array index expression" but comma is separating function arguments

Question

MSVC reports

warning C4709: comma operator within array index expression

on the following line:

intersections[img::at(rotJ, rotI)];

Without knowing more, is there any chance that this warning is valid?

"any chance"? Sure, for example you could have `#define at x +` which would make this not actually a function call. But that doesn't seem likely to be the case. — interjay, Jun 27 '20 at 09:41
@interjay Haha, I just *knew* someone would come up with some weird `#define`. — Museful, Jun 27 '20 at 09:47

score 2 · Accepted Answer · answered Jun 27 '20 at 09:59

2

The warning C4709: comma operator within array index expression is a rather buggy warning and has numerous reports all over the internet. See for e.g this or this or this (9 years old).

So the answer is, it is misleading.

Note that if someone were to use the comma-operator within the array index:

int a[3] = {1, 2, 3};
cout << a[1, 2]; // outputs 3

answered Jun 27 '20 at 09:59

Waqar

1

Maybe interesting to know is that the use of the comma operator in the operator[] is deprecated in C++20 – JVApen Jun 27 '20 at 10:35
Good things happening ;) – Waqar Jun 27 '20 at 10:36

1 Answers1