clog(3)

💖 clog(3) — bestie edition 💖

ok so we're in the Library Functions Manual and today's main character is clog(3) 🫶 grab a snack, this one's actually so cute once you get it.

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✨ NAME ✨

clog, clogf, clogl — the natural logarithm of a complex number 🌸

✨ LIBRARY ✨

Math library (libm, link it with -lm) ✨

✨ SYNOPSIS ✨

lowkey the whole vibe is right here:

#include <complex.h>

double complex clog(double complex z);
float complex clogf(float complex z);
long double complex clogl(long double complex z);

✨ DESCRIPTION ✨

okay so these functions calculate the complex natural logarithm of z, and there's a branch cut along the negative real axis 💅 (yes, the cut is part of the lore, we don't make the rules).

The logarithm clog() is the inverse function of the exponential cexp(3). So like, if y = clog(z), then z = cexp(y) 🦋. And the imaginary part of y is chosen in the interval [-pi,pi] — she stays in her lane, no cap.

One has:

clog(z) = log(cabs(z)) + I * carg(z)

heads up bestie 😭 note that z close to zero will cause an overflow. it's giving danger, so watch out for that.

✨ ATTRIBUTES ✨

for an explanation of the terms used in this section, see attributes(7) 👑

• Interface: clog(), clogf(), clogl()
• Attribute: Thread safety
• Value: MT-Safe

so yeah, thread safety is MT-Safe, we love a safe girlie ✨

✨ STANDARDS ✨

C11, POSIX.1-2008. periodt 💅

✨ HISTORY ✨

glibc 2.1. And also C99, POSIX.1-2001 — she's been iconic for a minute 👑

✨ SEE ALSO ✨

cabs(3), cexp(3), clog10(3), clog2(3), complex(7) 🌈

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and that's the whole page bestie 🎀 iykyk. this lil masterpiece came to you from Linux man-pages 6.20, dated 2026-02-08, and yes it's a clog(3) situation 💜 mwah, go log something complex 🧚