iswupper(3)

💅 iswupper — bestie, is this wide char uppercase or nah?

okay so picture this: you're deep in <wctype.h> land, you got a wide character, and you just need to know — is it giving UPPERCASE energy or not? that's literally the whole job of iswupper. she's the wide-character glow-up of isupper(3), and she eats every time. ✨

library situation: Standard C library (libc, -lc). yes bestie, the one you already have. 🫶

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✨ SYNOPSIS ✨

#include <wctype.h>

int iswupper(wint_t wc);

like… two lines. she's lowkey iconic for that. 🎀

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🦋 DESCRIPTION 🦋

so iswupper() is the wide-character equivalent of the isupper(3) function — same vibe, wider characters. her whole thing is testing whether wc is a wide character that belongs to the wide-character class "upper".

and now for the class lore, because the family tree here is deep:

• the class "upper" is a subclass of "alpha" 🧚
• and since she's in "alpha", she's also a subclass of "alnum", of "graph", and of "print"

and because family drama means exclusions, let's do the ✨vibe check✨ on who she does not hang out with:

• being a subclass of "print" means "upper" is disjoint from "cntrl" — no control characters in this clique, periodt 💀
• being a subclass of "graph" means "upper" is disjoint from "space" and its subclass "blank" — she does not do whitespace, nope
• being a subclass of "alnum" means "upper" is disjoint from "punct" — no punctuation allowed, sorry not sorry
• being a subclass of "alpha" means "upper" is disjoint from "digit" — numbers, you are NOT on the list 🙈

now the actual membership rules, fr fr:

• the class "upper" contains at least those characters wc which are equal to towupper(wc) and different from towlower(wc) 👑
• and the class "upper" always contains at least the letters 'A' to 'Z' — like, always. non-negotiable. 💖

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🔥 RETURN VALUE 🔥

• if wc is a wide character belonging to the wide-character class "upper" → returns nonzero ✅
• otherwise → returns zero ❌

that's it. binary queen. 🌈

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💜 ATTRIBUTES 💜

for an explanation of the terms used in this section, see attributes(7). here's the tea:

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

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⭐ STANDARDS ⭐

• C11, POSIX.1-2008

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🌸 HISTORY 🌸

• POSIX.1-2001, C99

so she's been around a minute. vintage but make it slay. 💅

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👑 NOTES 👑

• the behavior of iswupper() depends on the LC_CTYPE category of the current locale. so like, change your locale, change your answers. iykyk 🌍
• also, real talk: this function is not very appropriate for dealing with Unicode characters, because Unicode knows about three cases: upper, lower, and title case. three. case. bestie. this function only knows two. 😭

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🎀 SEE ALSO 🎀

• isupper(3)
• iswctype(3)
• towupper(3)

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and that's the whole page, pookie 🫶 this was iswupper from the Linux man-pages 6.20, dated 2026-02-08. go forth and test your wide chars with main character energy. bye bestie!! 💖✨🦋