<bitset> is a fixed-size bitfield: each bit is independently addressable and can be set, cleared, or tested. It's more memory-efficient than std::vector<bool> for large fixed-size bit arrays.

Use it for flags, masks, or when you need to track individual bits of a large quantity—like tracking active threads in a thread pool or implementing a sparse boolean matrix.

This example sets and manipulates individual bits in an 8-bit set, checking values, counting set bits, and flipping bits.

// compile: g++ -std=c++11 -o bitsetexample bitsetexample.cpp
// run: ./bitsetexample
// description: flag management with bitset
 
#include <bitset>
#include <iostream>
 
int main() {
    std::bitset<8> flags;
 
    flags.set(2);
    flags.set(5);
 
    std::cout << "bitset: " << flags << "\n";
    std::cout << "bit 2 is set: " << flags[2] << "\n";
    std::cout << "count of set bits: " << flags.count() << "\n";
 
    flags.flip(2);
    std::cout << "after flip(2): " << flags << "\n";
 
    return 0;
}