gcvt(3)

💖 gcvt(3) — the "float goes in, string comes out" page 💖

okay so bestie, you found the gcvt page in the Library Functions Manual and honestly? this one is a little vintage. it's giving my grandma's encyclopaedia but make it C. let's get into it 🫶

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✨ NAME ✨

gcvt — convert a floating-point number to a string

no fr that's literally it, that's the whole job 💅

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🌸 LIBRARY 🌸

Standard C library (libc, -lc)

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🎀 SYNOPSIS 🎀

#include <stdlib.h>

char *gcvt(double number, int ndigit, char *buf);

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

gcvt():

• Since glibc 2.17:

(_XOPEN_SOURCE >= 500 && ! (_POSIX_C_SOURCE >= 200809L))
    || /* glibc >= 2.20 */ _DEFAULT_SOURCE
    || /* glibc <= 2.19 */ _SVID_SOURCE

• glibc 2.12 to glibc 2.16:

(_XOPEN_SOURCE >= 500 && ! (_POSIX_C_SOURCE >= 200112L))
    || _SVID_SOURCE

• Before glibc 2.12:

_SVID_SOURCE || _XOPEN_SOURCE >= 500

bestie the way these macros gatekeep 😭 like okay girl, define your feature test macros or she's simply not showing up. copy them exactly, no cap, one wrong character and the compiler gets an attitude.

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🦋 DESCRIPTION 🦋

So gcvt() takes your number, glows it up, and converts it into a minimal length null-terminated ASCII string, then tucks that result into buf. iconic behaviour honestly.

And she's picky about significant digits: it produces ndigit significant digits, and it'll pick either printf(3) F format or E format for the fit. it decides. you don't. main character energy for real 🔥

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⭐ RETURN VALUE ⭐

gcvt() returns buf. that's it. that's the whole return value. she hands you back the thing you gave her, now with a cute string in it 💜

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💅 ATTRIBUTES 💅

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

• gcvt() — Thread safety: MT-Safe

(vibe check: passed, she's thread-safe, go off queen 👑)

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🌈 STANDARDS 🌈

None.

not a single one. she's unstandardised, she's free, she's ✨unbothered✨. periodt.

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🍓 HISTORY 🍓

• Marked as LEGACY in POSIX.1-2001.
• POSIX.1-2008 removed it, recommending the use of sprintf(3) instead (though snprintf(3) may be preferable).

okay so real talk bestie: if you're writing new code, maybe don't reach for this one 😭 she's legacy-coded. the manual literally says use sprintf(3) instead, and side-eyes it by noting snprintf(3) may be preferable. do with that information what you will 🫶

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🧚 SEE ALSO 🧚

• ecvt(3)
• fcvt(3)
• sprintf(3)

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and that's the page!! go forth and convert your floats, bestie 💖✨

this chaotic lil rewrite came from the Linux man-pages 6.20 release, dated 2026-02-08 — original gcvt(3) page, now serving looks in lowercase 🎀