fmax(3)

💖 fmax(3) — the "who's bigger bestie" page 💖

okay so first things first, this is a page from the Library Functions Manual, and it's all about the trio of legends known as fmax, fmaxf, and fmaxl. They look at two floating-point numbers and are like "which one of you is serving more magnitude" and then hand you the winner. no cap, that's the whole job. 🦋

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🌸 NAME 🌸

fmax, fmaxf, fmaxl — determine maximum of two floating-point numbers

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📚 LIBRARY 📚

Math library (libm, -lm) 💅

bestie if your link line doesn't have -lm she will simply not show up, and you'll be sitting there confused like "where is my max" 😭

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✨ SYNOPSIS ✨

#include <math.h>

double fmax(double x, double y);
float fmaxf(float x, float y);
long double fmaxl(long double x, long double y);

🎀 Feature Test Macro Requirements for glibc 🎀

(peep feature_test_macros(7) for the whole lore, but here's the tea 🍓)

• fmax(), fmaxf(), fmaxl():
  • _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L

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💅 DESCRIPTION 💅

These functions return the larger value of x and y.

that's it. that's the function. it's giving "pick the bigger one" and honestly? iconic. no drama, no side quests, just pure comparison energy. 🌈

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💖 RETURN VALUE 💖

These functions return the maximum of x and y.

and now for the plot twist that makes her so beloved:

• If one argument is a NaN, the other argument is returned. 👑 (yes queen, she does NOT let a NaN ruin the whole vibe, she just hands you the other one)
• If both arguments are NaN, a NaN is returned. 💀 (yeah if literally everyone is a NaN then... that's what you get back, fr fr)

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🙈 ERRORS 🙈

No errors occur.

not one. zero. none. she doesn't do errors, she just does maximum. 😌✨

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🌟 ATTRIBUTES 🌟

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

(no tables in the group chat, so here's the same info as bullets, bestie 🧚)

• Interface: fmax(), fmaxf(), fmaxl()
• Attribute: Thread safety
• Value: MT-Safe

MT-Safe means you can call her from multiple threads and she will not have a breakdown. multi-threaded main character energy, we love to see it. 🔥

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🦋 STANDARDS 🦋

C11, POSIX.1-2008.

certified, standardized, and standing on business. ⭐

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💜 HISTORY 💜

glibc 2.1. C99, POSIX.1-2001.

she's been around since glibc 2.1 and knows things, okay? elder but still that girl. 🎀

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👀 SEE ALSO 👀

• fdim(3)
• fmin(3)

(go say hi to fmin(3), she's literally the opposite vibe and also a queen 🫶)

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and that's the whole page bestie!! 💖✨ this was brought to you by Linux man-pages 6.20, dated 2026-02-08 — so you know it's fresh, you know it's slay, you know it's giving official documentation. now go fmax something and thrive 😭💅🌈