iswlower(3)

💖 iswlower(3) — bestie's guide to lowercase wide characters 💖

okay so real quick before we dive in: this is the manual page for iswlower(3), and yes she is a wide-character girlie 💅

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🌸 NAME 🌸

iswlower — test for lowercase wide character

📚 LIBRARY 📚

Standard C library (libc, -lc)

✨ SYNOPSIS ✨

#include <wctype.h>

int iswlower(wint_t wc);

🦋 DESCRIPTION 🦋

okay so iswlower() is literally the wide-character equivalent of the islower(3) function. no cap. what it does is test whether wc is a wide character that belongs to the wide-character class "lower". that's it, that's the job 🫶

now here's the family tree moment, because "lower" is NOT out here alone, she's nested 💅:

• the wide-character class "lower" is a subclass of the wide-character class "alpha", and therefore also a subclass of "alnum", of "graph", and of "print". iconic lineage honestly 👑

and because of that nesting, she's automatically disjoint from a whole bunch of other classes:

• being a subclass of "print", the class "lower" is disjoint from the class "cntrl"
• being a subclass of "graph", the class "lower" is disjoint from the class "space" and its subclass "blank"
• being a subclass of "alnum", the class "lower" is disjoint from the class "punct"
• being a subclass of "alpha", the class "lower" is disjoint from the class "digit"

so what's actually in there? the wide-character class "lower" contains at least those characters wc which are equal to towlower(wc) and different from towupper(wc). that's the vibe check ✅

and the bare minimum she always has? the wide-character class "lower" always contains at least the letters 'a' to 'z'. periodt. 🍓

🎀 RETURN VALUE 🎀

iswlower() returns nonzero if wc is a wide character belonging to the wide-character class "lower". otherwise? it returns zero. simple as that, bestie 💖

🔥 ATTRIBUTES 🔥

for the explanation of the terms used in this section, go peek at attributes(7) — iykyk.

• Interface: iswlower()
• Attribute: Thread safety
• Value: MT-Safe locale

🌈 STANDARDS 🌈

C11, POSIX.1-2008. she's certified ✨

💜 HISTORY 💜

POSIX.1-2001, C99. she's been around, she's a legend, she's the blueprint 🕰️

⭐ NOTES ⭐

okay so heads up: the behavior of iswlower() depends on the LC_CTYPE category of the current locale. so like, know your locale before you come for her 💀

and ngl, this function is not very appropriate for dealing with Unicode characters, because Unicode knows about three cases: upper, lower, and title case. so iswlower() is out here living in a two-case world while Unicode is doing three. not her fault, just the lore 🙈

👑 SEE ALSO 👑

islower(3), iswctype(3), towlower(3)

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that's the whole page bestie, go forth and lowercase 🌸💅

this was Linux man-pages 6.20, dated 2026-02-08 — ily, stan the man-pages maintainers 🫶