Enforce sequencing between operand

本文总结能够保证evaluation order的方式。

stackoverflow Is comma operator free from side effect?

For example for such statement:

c += 2, c -= 1

Is it true that c += 2 will be always evaluated first, and c in second expression c-= 1 will always be updated value from expression c += 2?

A

Yes, it is guaranteed by the standard, as long as that comma is a non-overloaded comma operator. Quoting n3290 §5.18:

josephmansfield C++ sequenced-before graphs

Example: i++ || i++

i++ || i++

This demonstrates the ability of some operators (namely ||, &&, and ,) to enforce sequencing between their operands. The standard states that every value computation and side effect associated with the left operand is sequenced before those of the right operand.