How is the comma operator being used here?

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C++ Comma Operator
Uses of C comma operator

I am not new to C++, but this is the first time I see the following code:

int a=0;
int b=(a=2,a+1);

That is C++ code. Can you tell me what is going on here? And how variable b gets value 3?

That was the code I saw. And what do you mean by horrible to read? You mean not to use comma operator in that case or what? — seeker, Oct 10 '12 at 17:12
@seeker - If we have to ask what the code does, it *is* horrible code. — Bo Persson, Oct 10 '12 at 17:25

Coding Mash · Accepted Answer · 2012-10-10T17:04:08.693

13

This code is equivalent to this:

int a = 2 ; 
int b = a + 1 ;

First expression to the left of comma gets evaluated, then the one to its right. The result of the right most expression is stored in the variable to the left of = sign.

Look up the comma operator for more details.

http://en.wikipedia.org/wiki/Comma_operator

edited Oct 10 '12 at 17:04

answered Oct 10 '12 at 16:49

Coding Mash

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Are you sure? I think the code is equivalent to `int b = a = 2; int b = a + 1;` notice the subtle difference – kimbaudi Jul 01 '16 at 17:27

score 3 · Answer 2 · answered Oct 10 '12 at 16:51

3

(a = 2, a + 1); return 3 because in general case operator (a, b) return b, and calculation in (a, b) started from right to left. So, in your case, (a = 2, a + 1) return a + 1, and after operator a = 2 was executed a + 1 return 3.

answered Oct 10 '12 at 16:51

Mikhail Viceman

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How is the comma operator being used here?

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