sin(3)

✨ sin(3) — the sine girlies 💖

okay so bestie, we're in section 3 of the manual (that's the library functions section, iykyk) and today's main character is sin. she's a Library Function and honestly? iconic. 🎀

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🌸 NAME 🌸

sin, sinf, sinl — the sine function, in three delicious flavors 💅

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📚 LIBRARY 📚

Math library — that's libm, and you link it with -lm. don't forget her or she will simply not show up. 😭

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✨ SYNOPSIS ✨

#include <math.h>

double sin(double x);
float sinf(float x);
long double sinl(long double x);

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

for sinf(), sinl():

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

like, yes, you have to ask for her nicely with the right macros. the vibes have ✨paperwork✨. 🫶

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💖 DESCRIPTION 💖

These functions return the sine of x, where x is given in radians. that's it, that's the whole thing. radians only, bestie — if you're out here passing degrees, that's on you and I can't help you. 😭

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🌈 RETURN VALUE 🌈

On success, these functions return the sine of x. slay. 💅

• If x is a NaN, a NaN is returned. (a NaN in, a NaN out — the circle of life 🦋)
• If x is positive infinity or negative infinity, a domain error occurs, and a NaN is returned. no cap, infinities are simply not invited to this party. 💀

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🔥 ERRORS 🔥

See math_error(7) for info on how to figure out whether an error actually happened when you called these functions, because they're lowkey subtle about it.

The following errors can occur:

• Domain error: x is an infinity — errno is set to EDOM (but see BUGS, bestie, there's lore 📖). An invalid floating-point exception (FE_INVALID) is raised.

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👑 ATTRIBUTES 👑

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

• sin(), sinf(), sinl() — Thread safety: MT-Safe ✅

(we love a thread-safe queen. no drama, no data races, just math. 🫶)

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⭐ STANDARDS ⭐

C11, POSIX.1-2008. periodt. 💅

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🦋 HISTORY 🦋

C99, POSIX.1-2001.

The variant returning double also conforms to SVr4, 4.3BSD, C89 — she's been around since basically forever, a true 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 yeah, on ancient systems, the error reporting was giving nothing. not me defending it, I'm just the messenger. 🙈

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🎀 SEE ALSO 🎀

acos(3), asin(3), atan(3), atan2(3), cos(3), csin(3), sincos(3), tan(3)

(the whole trig friend group 💜 they're all invited to the group chat)

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and that's the page, bestie!! this was sin(3) from Linux man-pages 6.20, dated 2026-02-08. go forth and sine responsibly ✨🌸💖