Bit flags in C

Setting, clearing, and testing individual bits.

unsigned set_bit(unsigned flags, int pos) {
    return flags | (1u << pos);
}

unsigned clear_bit(unsigned flags, int pos) {
    return flags & ~(1u << pos);
}

int test_bit(unsigned flags, int pos) {
    return (flags >> pos) & 1u;
}

How it works

1. 1u << pos builds a mask for one bit.
2. | sets, & ~ clears that bit.
3. Shifting then & 1u tests it.

Keywords and builtins used here

• clear_bit
• int
• return
• set_bit
• test_bit
• unsigned

The run, in numbers

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Step 1 of 2 in Bit manipulation, step 17 of 20 in Data structures & algorithms.

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