tan(3)

✨ tan(3) — the tangent function, but make it make sense ✨

okay so bestie, welcome to the Library Functions Manual entry for tan(3) 💖 this is a section 3 page (that's the C library girlies) and it's literally just... the tangent function. three flavors of it. let's go 🦋

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🎀 NAME 🎀

tan, tanf, tanl — tangent function

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📚 LIBRARY 📚

Math library (libm, -lm)

link it with -lm or she will simply Not work. no cap.

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🌸 SYNOPSIS 🌸

#include <math.h>

double tan(double x);
float tanf(float x);
long double tanl(long double x);

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

tanf(), tanl():
    _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
        || /* Since glibc 2.19: */ _DEFAULT_SOURCE
        || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

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💅 DESCRIPTION 💅

These functions return the tangent of x, where x is given in radians. that's it. that's the whole description. radians, not degrees — I know, I know, tragic, but that's the vibe 🌈

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⭐ RETURN VALUE ⭐

On success, these functions return the tangent of x. iconic behaviour, honestly 👑

If x is a NaN, a NaN is returned. (NaN in, NaN out, the circle of life 💀)

If x is positive infinity or negative infinity, a domain error occurs, and a NaN is returned. she said nope 🙈

If the correct result would overflow, a range error occurs, and the functions return HUGE_VAL, HUGE_VALF, or HUGE_VALL, respectively, with the mathematically correct sign. so like, huge but make it signed ✨

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😭 ERRORS 😭

See math_error(7) for information on how to determine whether an error has occurred when calling these functions. (fr fr, go read it, it's the receipts girlie 🧾)

The following errors can occur:

• Domain error: x is an infinity — errno is set to EDOM (but see BUGS). An invalid floating-point exception (FE_INVALID) is raised. 🚨
• Range error: result overflow — An overflow floating-point exception (FE_OVERFLOW) is raised.

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👑 ATTRIBUTES 👑

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

• tan(), tanf(), tanl() — Thread safety: MT-Safe 🫶

MT-Safe means you can call her from multiple threads and she will not start drama. we love a low-maintenance queen.

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🌈 STANDARDS 🌈

C11, POSIX.1-2008.

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🕰️ HISTORY 🕰️

C99, POSIX.1-2001.

The variant returning double also conforms to SVr4, 4.3BSD, C89. yes she's been around, she's a legacy icon 💜

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💀 BUGS 💀

Before glibc 2.10, the glibc implementation did not set errno to EDOM when a domain error occurred. so if you're on some ancient glibc, don't trust the errno, bestie, check the floating-point exception instead 😭

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🔥 SEE ALSO 🔥

acos(3), asin(3), atan(3), atan2(3), cos(3), ctan(3), sin(3)

the whole trig friend group. go say hi 🍓

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okay that's the page!! this cutie comes to you from Linux man-pages 6.20, dated 2026-02-08, and she ate, no crumbs 💅✨🎀