Are assignment operators "required" to return?

Question

According to the C++ standard, can I be sure that assignment operators for built-in variables return (the original value)?

Or is this implementation dependent (yet simply have most popular compilers implemented this)?

Answer 1

Yes, it is guaranteed:

5.17 Assignment and compound assignment operators

The assignment operator (=) and the compound assignment operators all group right-to-left. All require a modifiable lvalue as their left operand and return an lvalue referring to the left operand.

This applies to built-in types. With user-defined types it can return anything.

Answer 2

It depends on what you mean by "the original value".

For example:

#include <iostream>
int main() {
    int i;
    std::cout << (i = 1.9) << "\n";
}

prints 1. The assignment expression yields the new value of the LHS (namely 1), not the "original value" of the RHS (1.9).

I'm not sure whether that's what you meant to ask about.