Why isn't the OR (||) logical operator being properly computed?

Question

When printing to the terminal, the OR operator is not being applied in C++.

MWE:

#include <iostream>
int main()
{
    std::cout << false || true;
    return 0;
}

https://en.cppreference.com/w/cpp/language/operator_precedence — teapot418, Feb 10 '23 at 22:27
@teapot418 :face-palm: you are right, hope this is not too dumb for SO — Hans, Feb 10 '23 at 22:29
related/dupe: https://stackoverflow.com/questions/75034962/why-vector-comparision-result-shows-error-when-not-put-in-parenthesis — NathanOliver, Feb 10 '23 at 22:31
The lesson to learn is always add ( ) so you never get it wrong :) — Dave S, Feb 10 '23 at 22:31
Unless the brackets make it wrong. But if programming were easy everybody would be doing it. — user4581301, Feb 10 '23 at 22:32

score 3 · Accepted Answer · answered Feb 10 '23 at 22:38

3

Shift operators have higher priority than logical operators.

So this statement

std::cout << false || true;

is equivalent to

( std::cout << false ) || ( true );

As a result the literal false will be outputted as integer 0.

If you want to output the literal true then you should write

std::cout << ( false || true );

answered Feb 10 '23 at 22:38

Vlad from Moscow

1

The answer is correct. To a novice the operator precedence in this case is probably surprising. If the `<<` operator was invented as a streaming operator it would have had lower precedence, but its original and alternative use as a bit-shift operator means that it has the precedence that it has. This is a general issue with operator overloading. As the answer illustrates, better use too many parenthesis than too few. I often put redundant parenthesis so that code can be understood without cross-checking the precedence table. – nielsen Feb 10 '23 at 22:58