tanh(3)

💖 tanh(3) — hyperbolic tangent, bestie edition 💖

okay so this is a page from the Library Functions Manual (section 3, the "library calls" girlies), and it's all about tanh and her two glow-up siblings tanhf and tanhl. buckle up, this one is short but she's iconic 🎀

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✨ NAME ✨

tanh, tanhf, tanhl — the hyperbolic tangent function 🦋

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📚 LIBRARY 📚

Math library, aka libm, and you link her with -lm (yes bestie, you have to pass the flag, she's not coming for free) ✨

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🌸 SYNOPSIS 🌸

#include <math.h>

double tanh(double x);
float tanhf(float x);
long double tanhl(long double x);

🧚 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

for tanhf() and tanhl():

_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
    || /* Since glibc 2.19: */ _DEFAULT_SOURCE
    || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

like, define one of those or the compiler is gonna act brand new, no cap 💀

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👑 DESCRIPTION 👑

These functions hand you back the hyperbolic tangent of x, and mathematically she is defined as:

tanh(x) = sinh(x) / cosh(x)

that's the whole vibe. sinh over cosh. girl math? no. real math 🌈

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💅 RETURN VALUE 💅

On success, these functions return the hyperbolic tangent of x. periodt.

• If x is a NaN, a NaN is returned. (garbage in, garbage out, she's not gonna lie to you 🙈)
• If x is +0 (-0), +0 (-0) is returned. signed zero stays signed, she remembers 🤝
• If x is positive infinity (negative infinity), +1 (-1) is returned. she saturates, she's chill like that 🔥

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😭 ERRORS 😭

No errors occur. not a single one. she simply does not miss. 💖

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🌈 ATTRIBUTES 🌈

For an explanation of the terms used in this section, see attributes(7).

• Interface: tanh(), tanhf(), tanhl()
• Attribute: Thread safety
• Value: MT-Safe

translation: she's MT-Safe, so go off, call her from all your threads, she's not gonna start drama 🫶

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⭐ STANDARDS ⭐

C11, POSIX.1-2008. she's certified, she's official, she passed the vibe check 👑

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🕰️ HISTORY 🕰️

C99, POSIX.1-2001. been that girl since the late 90s fr fr.

The variant returning double also conforms to SVr4, 4.3BSD, C89. so basically the double version has been around forever, a true elder icon 🌸

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🦋 SEE ALSO 🦋

acosh(3), asinh(3), atanh(3), cosh(3), ctanh(3), sinh(3)

the whole hyperbolic friend group!! go say hi, they're all obsessed with each other 🫶✨

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and that's the tea, bestie 💜 this was pulled from Linux man-pages 6.20, dated 2026-02-08 — so you know it's fresh, it's current, and it ate. mwah. 💅🎀🦋