How does comma operator work during assignment?

Question

int a = 1;
int b = (1,2,3);
cout << a+b << endl; // this prints 4

1. Is (1,2,3) some sort of structure in c++ (some pri

Answer 1

(1,2,3) is an expression using two instances of the comma operator. The comma operator evaluates its left operand, then there's a sequence point and then it evaluates its right operand. The value of the comma operator is the result of the evaluation of the right hand operand, the result of evaluating the left operand is discarded.

int b = (1,2,3);

is, therefore, equivalent to:

int b = 3;

Most compilers will warn about such a use of the comma operand as there is only ever a point to using a comma operator if the left hand expression has some side effect.