swab(3)

💖 swab(3) — swap adjacent bytes 💖

okay bestie, welcome to the swab(3) page, straight out of the Library Functions Manual section 3 (the "library functions" girlies, you know the ones). this is a tiny little function with big main character energy and honestly? she ate. let's get into it. ✨

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🌸 NAME 🌸

swab — swap adjacent bytes

like literally that's it, that's the whole gig. adjacent bytes get swapped. boom. 🦋

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📚 LIBRARY 📚

Standard C library (libc, -lc)

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🎀 SYNOPSIS 🎀

#define _XOPEN_SOURCE       /* See feature_test_macros(7) */
#include <unistd.h>

void swab(ssize_t n;
          const void from[restrict n], void to[restrict n],
          ssize_t n);

okay so yes, bestie, you do gotta define _XOPEN_SOURCE before you pull in <unistd.h> — feature_test_macros(7) is right there if you wanna know why. 🙈

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✨ DESCRIPTION ✨

so here's the vibe. swab() copies n bytes from the array that from points at, over to the array that to points at — and while it's doing that, it exchanges adjacent even and odd bytes. like it grabs byte 0 and byte 1 and swaps them, then byte 2 and byte 3, and so on. slay.

what is this even for, you ask? it's for exchanging data between machines that have different low/high byte ordering. so if your machines disagree about endianness, this little icon is the mutual friend who smooths things over. 🫶

now the ✨ caveats ✨, and listen closely because this part matters:

• if n is negative, this function does literally nothing. no cap. it just vibes.
• if n is positive and odd, it handles n-1 bytes the normal way, and then does something unspecified with that last byte. 💀 unspecified!! which is just a fancy way of saying "we're not telling you, don't ask."

tl;dr — n should be even. like, please. just make it even. protect your peace. 🧚

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💅 RETURN VALUE 💅

swab() returns no value. nothing. zero. she gives nothing and she's not sorry. 😌

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👑 ATTRIBUTES 👑

if you wanna know what these terms mean, go peek at attributes(7) — it's got the whole glossary.

• Interface: swab()
  • Attribute: Thread safety
  • Value: MT-Safe

yup, she's MT-Safe. multi-thread approved. go off queen. 🔥

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🌈 STANDARDS 🌈

POSIX.1-2008.

certified, standardized, official. periodt. 💅

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🦋 HISTORY 🦋

POSIX.1-2001, SVr4, 4.3BSD.

she's been on the scene for a minute — an absolute elder stateswoman of byte swapping. respect the icon. 👑

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🔍 SEE ALSO 🔍

• bstring(3)

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and that's the whole page bestie!! go forth and swap those adjacent bytes responsibly (with an even n, fr fr) 🌸💖✨

this lil dispatch came to you from Linux man-pages 6.20, dated 2026-02-08 — mwah, love u, bye!! 🎀🫶