a64l(3)

💖 a64l — the base-64 glow-up page (section 3 of the manual, bestie)

okay so you found yourself a a64l(3) page and you're like "what even is this" — don't worry, I got you. This is the Library Functions Manual entry for a64l and l64a, and by the end you're gonna be converting longs to base-64 like it's nothing. no cap. ✨

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🌸 NAME 🌸

a64l, l64a — convert between long and base-64

📚 LIBRARY 📚

Standard C library (libc, -lc)

✨ SYNOPSIS ✨

#include <stdlib.h>

long a64l(const char *str64);
char *l64a(long value);

🎀 Feature Test Macro Requirements for glibc 🎀

(peep feature_test_macros(7) for the tea, bestie)

a64l(), l64a():

_XOPEN_SOURCE >= 500
    || /* glibc >= 2.19: */ _DEFAULT_SOURCE
    || /* glibc <= 2.19: */ _SVID_SOURCE

💅 DESCRIPTION 💅

So like, these two functions are a little conversion duo 🫶 — they take you back and forth between 32-bit long integers and little-endian base-64 ASCII strings. And those strings? They're length zero to six. Yep, tiny. adorable.

Couple things you gotta know:

• If the string you hand to a64l() is longer than six, it literally only looks at the first six bytes. the rest? ignored. 💀
• If your type long has more than 32 bits, then l64a() only uses the low order 32 bits of value, and a64l() sign-extends its 32-bit result.

🔢 the 64 digits in the base-64 system 🔢

this is the whole alphabet, memorize it, it's giving secret code:

'.'  represents a 0
'/'  represents a 1
0-9  represent  2-11
A-Z  represent 12-37
a-z  represent 38-63

and here's the flex that makes it click:

So 123 = 59*64^0 + 1*64^1 = "v/".

see?? 59 is v and 1 is /. math ate. 🔥

👑 ATTRIBUTES 👑

for an explanation of the terms used in this section, go look at attributes(7). But here's the breakdown:

• l64a() — Thread safety: MT-Unsafe race:l64a 😭 (yeah. she's got a race condition. we'll get to that)
• a64l() — Thread safety: MT-Safe 👑

⭐ STANDARDS ⭐

POSIX.1-2008.

🌈 HISTORY 🌈

POSIX.1-2001.

💜 NOTES 💜

okay bestie, here's the important stuff, read every line:

• The value returned by l64a() may be a pointer to a static buffer, and it can possibly be overwritten by later calls. so don't be out here holding onto it like it's yours. 😭
• The behavior of l64a() is undefined when value is negative. fr fr, don't do it.
• If value is zero, it returns an empty string. cute, minimal, iconic.
• Heads up: these functions were broken before glibc 2.2.5 — they put the most significant digit first. wrong order bestie, we don't stan.
• And one more: this is not the encoding used by uuencode(1). not the same thing. don't mix them up or you'll be sad. 🥲

🦋 SEE ALSO 🦋

• uuencode(1)
• strtoul(3)

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okay that's the whole page, you're officially a base-64 girlie now, go forth and convert 💖 this was a64l(3) from Linux man-pages 6.20, dated 2026-02-08 — periodt. 🎀✨