modf(3)

💖 modf — bestie edition 💖

okay so this is the manual page for modf, modff, and modfl — the <pink>libm</pink> girlies that literally split your floating-point number into two pieces. It's <cyan>modf(3)</cyan> from the Linux man-pages, and yes we're doing this. 🎀

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✨ NAME ✨

modf, modff, modfl — pull the signed integral part and the fractional part out of a floating-point number 🦋

📚 LIBRARY 📚

Math library, aka <mint>libm</mint> — link it with <yellow>-lm</yellow>.

🌸 SYNOPSIS 🌸

#include <math.h>

double modf(double x, double *iptr);
float modff(float x, float *iptr);
long double modfl(long double x, long double *iptr);

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

For modff(), modfl():

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

like, yes, the whole chain, don't skip any of it bestie 💅

💫 DESCRIPTION 💫

These functions take the argument x and snap it in half — one integral part, one fractional part — and <hotpink>both of them keep the same sign as x</hotpink>. The integral part gets yeeted into the location that iptr points to. 📍

🔥 RETURN VALUE 🔥

They hand you back the <purple>fractional part</purple> of x. periodt.

• If x is a NaN, a NaN comes back, and *iptr is set to a NaN. 😭 (yes, both. NaN all the way down.)
• If x is positive infinity (or negative infinity), then +0 (or -0) is returned, and *iptr is set to positive infinity (or negative infinity). ♾️

💀 ERRORS 💀

No errors occur. not a single one. she's chill like that. 💅

👑 ATTRIBUTES 👑

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

• Interface: modf(), modff(), modfl()
• Attribute: Thread safety
• Value: MT-Safe ✨ (yes she's safe to run in threads, we love a secure queen)

🌈 STANDARDS 🌈

C11, POSIX.1-2008.

🕰️ HISTORY 🕰️

• C99, POSIX.1-2001.
• The variant that returns double also conforms to SVr4, 4.3BSD, C89. look at her, legacy icon behavior 👑

🔭 SEE ALSO 🔭

• frexp(3)
• ldexp(3)

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and that's the whole page, bestie 🫶 this was Linux man-pages <pink>6.20</pink>, dated <lavender>2026-02-08</lavender>, and modf(3) ate and left no crumbs. 💖✨🎀