lround(3)

💖 lround(3) — the "round it, but give me an actual integer" girlies 💖

okay bestie so this is a page from the Library Functions Manual, and it's all about the lround family — the ones who take your float and hand you back a whole number, no decimal drama, no cap. ✨

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🎀 NAME 🎀

lround, lroundf, lroundl, llround, llroundf, llroundl — round to nearest integer

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📚 LIBRARY 📚

Math library (libm, -lm)

like she lives in libm, so if you're linking, don't forget your -lm, bestie, or she's gonna ghost you. 🫶

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✨ SYNOPSIS ✨

#include <math.h>

long lround(double x);
long lroundf(float x);
long lroundl(long double x);

long long llround(double x);
long long llroundf(float x);
long long llroundl(long double x);

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

All functions shown above:

_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L

so yeah, you gotta define that or the compiler is gonna be like "who?? never heard of her." 💀

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💅 DESCRIPTION 💅

These functions round their argument to the nearest integer value, rounding halfway cases away from zero, regardless of the current rounding direction (see fenv(3)).

okay that's the tea right there — halfway cases go away from zero, always, no matter what your current rounding direction is doing. she does NOT check the vibe of fenv(3). she has her own agenda. periodt. 👑

Note that unlike the round(3) and ceil(3), functions, the return type of these functions differs from that of their arguments.

that's literally the whole plot twist: she does not return the same type you handed her. that's the entire point of her existence. it's giving "i changed, bestie." 🦋

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👑 RETURN VALUE 👑

These functions return the rounded integer value.

If x is a NaN or an infinity, or the rounded value is too large to be stored in a long (long long in the case of the ll* functions), then a domain error occurs, and the return value is unspecified.

🚨 bestie listen — NaN, infinity, or a number so big it won't fit in a long (or long long for the ll* crew)? that's a domain error and the return value is unspecified. unspecified means don't trust it, do not pass go, do not collect. 😭

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🍓 ERRORS 🍓

See math_error(7) for information on how to determine whether an error has occurred when calling these functions.

The following errors can occur:

• Domain error: x is a NaN or infinite, or the rounded value is too large — An invalid floating-point exception (FE_INVALID) is raised.

These functions do not set errno.

ngl, that last line is the one that gets people. no errno for you, so don't go checking it and feeling confused. 🙈 this is why math_error(7) exists, go read her.

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🌈 ATTRIBUTES 🌈

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

• Interface: lround(), lroundf(), lroundl(), llround(), llroundf(), llroundl()
• Attribute: Thread safety
• Value: MT-Safe

MT-Safe, meaning she's safe to hang with from multiple threads at once. multithreaded icon behavior, honestly. 💜

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⭐ STANDARDS ⭐

C11, POSIX.1-2008.

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🧚 HISTORY 🧚

glibc 2.1. C99, POSIX.1-2001.

she's been around. she's a legacy icon, a vintage queen, and she's still slaying. ✨

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🔥 SEE ALSO 🔥

ceil(3), floor(3), lrint(3), nearbyint(3), rint(3), round(3)

like her whole friend group, go say hi, they're all doing similar-but-different things and yes you have to know the difference, sorry bestie, that's the assignment. 💖

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🌸 cute lil sign-off: this page is from Linux man-pages 6.20, dated 2026-02-08, and it's all about lround(3) — round to nearest integer, halfway cases away from zero, and that's on lround(3) 💅🎀🦋