Wrong result when XOR'ing two std::bitset

Question

#include <bitset>
#include <iostream>

int main() {
    std::bitset<8> a = 10101010;
    std::bitset<8> b = 11111111;

    std::cout << (a ^ b);
}

When running the following code the result is:

11010101

Expected output is:

01010101

Am I doing something wrong?

Answer 1

You initialize a and b with values which are decimal int literals (10101010, 11111111).

In order to use binary literals you need the 0b prefix:

#include <bitset>
#include <iostream>

int main() {
    std::bitset<8> a = 0b10101010;
    std::bitset<8> b = 0b11111111;

    std::cout << (a ^ b);
}

Output:

01010101

Live demo

More info about such literals: Integer literal.

A side note:
As mentioned above the current values you use are decimal integer literals.
But there is also the 0 prefix (without b) for octal literals.
So if you used e.g. 01010101 to initialize a or b, it would have been interpreted as an octal (base 8) value.