towlower(3)

💖 towlower(3) — the wide-char lowercase glow-up 💖

okay bestie, so this one lives in the Library Functions Manual, and it's literally just: take a wide character, make it lowercase. that's it. that's the whole vibe. two functions, towlower and towlower_l, and they are not complicated, i promise. 🦋

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📚 LIBRARY

Standard C library (libc, -lc) — yeah girl, she's been in the group chat since forever. 👑

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✨ SYNOPSIS

#include <wctype.h>

wint_t towlower(wint_t wc);
wint_t towlower_l(wint_t wc, locale_t locale);

🎀 Feature Test Macro Requirements for glibc

(if you don't know what these are, go read feature_test_macros(7), i'll wait 💅)

towlower_l():

• Since glibc 2.10: _XOPEN_SOURCE >= 700
• Before glibc 2.10: _GNU_SOURCE

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🌸 DESCRIPTION

So here's the tea. towlower() is literally the wide-character version of tolower(3) — same energy, wider chars. 🙈

Here's exactly what she does:

• if wc is an uppercase wide character, AND there's a lowercase equivalent in the current locale → she gives you back that lowercase equivalent
• in all other cases → wc comes right back to you, unchanged, no notes

Then there's towlower_l(), which does the exact same task but bases the conversion on the character type info in the locale you pass as locale. same job, different locale, iykyk. 🧚

⚠️ bestie please listen: the behavior of towlower_l() is undefined if locale is the special locale object LC_GLOBAL_LOCALE (go check duplocale(3)) or if it's not a valid locale object handle. undefined. we don't do that. 💀

And about the argument wc — it must be representable as a wchar_t and be a valid character in the locale, or it can be the value WEOF. that's the rule, periodt.

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🫶 RETURN VALUE

• if wc was convertible to lowercase → towlower() returns its lowercase equivalent 💖
• otherwise → it returns wc

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🔥 ATTRIBUTES

for an explanation of the terms used in this section, see attributes(7). (the original is a whole table but we're doing bullets, slay)

• towlower() — Thread safety: MT-Safe locale
• towlower_l() — Thread safety: MT-Safe

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👑 STANDARDS

towlower()

• C11, POSIX.1-2008 (XSI).

towlower_l()

• POSIX.1-2008.

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👑 STANDARDS (yes, again, the manpage said it twice and we respect the canon)

towlower()

• C99, POSIX.1-2001 (XSI).
• Obsolete in POSIX.1-2008 (XSI). 😭 she's a legacy queen.

towlower_l()

• glibc 2.3.
• POSIX.1-2008.

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💜 NOTES

• the behavior of these functions depends on the LC_CTYPE category of the locale. that's the whole plot. 🌈
• real talk though: these functions are not very appropriate for dealing with Unicode characters, because Unicode knows about three cases: upper, lower, and title case. three. she can't hold all that. 🙈

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🦋 SEE ALSO

iswlower(3), towctrans(3), towupper(3), locale(7)

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and that's the whole page babes ✨ this was Linux man-pages 6.20, dated 2026-02-08, brought to you by the towlower(3) girlies. go lowercase something. no cap. 💅🎀