SETBIT(9)

okay so you clicked into setbit(9) — the Kernel Developer's Manual page — and honestly? iconic. This is the group chat for the setbit family of macros, aka the bitmap besties 💅✨

💖 NAME 💖

setbit — macros related to bitmaps 🎀

✨ SYNOPSIS ✨

First, pull in the header like the good little kernel gremlin you are:

#include <sys/param.h>

Then the whole squad shows up:

void
setbit(array, x);

void
clrbit(array, x);

int
isset(array, x);

int
isclr(array, x);

🦋 DESCRIPTION 🦋

The setbit family of macros operate with bitmaps, also known as bit arrays. No cap, that's the whole vibe 🫶

In a nutshell: setbit() sets the bit x in array; clrbit() clears it; isset() tests whether x is set; and isclr() returns 1 if x is not set. Slay, concise king 👑✨

🌸 EXAMPLES 🌸

Here's the example, bestie: a buffer of 10 chars gets treated as an array of 80 bits:

char buf[10];

...

setbit(buf, 12);        /* set the fifth bit in the second byte */

That comment is literally doing the most and I love that for it 💖

💅 SEE ALSO 💅

• bitmap(3) — the other bitmap bestie
• bitstring(3) — the bitstring bestie, go say hi 🦋

⚠️ CAVEATS ⚠️

The number of valid bits in a given array is assumed to be multiple of CHAR_BIT — that's the number of bits for smallest object that is not a bit-field. So yeah, keep that in mind before you start vibing with arbitrary bit counts 😭💀

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xoxo, this page is from Debian 💖 dated December 4, 2012 ✨ — SETBIT(9) out, bestie! 🎀🦋