std::islower(std::locale)(3)

🎀 NAME 🎀

okay bestie, welcome to std::islower(std::locale)(3) — yes, that's the title — from the C++ Standard Libary manual. This page is literally about std::islower(std::locale): the locale-aware lowercase check. No gatekeeping, we got you. 💅

✨ Synopsis ✨

First things first, it's defined in header <locale> — say it with me. ✨

template< class CharT >
bool islower( CharT ch, const locale& loc );

So what does it do? It checks if the given character is classified as a lowercase alphabetic character by the given locale's std::ctype facet. That's the whole vibe check. 👑

🌸 Parameters 🌸

• ch — character. that's the one we're checking, bestie.
• loc — locale. this is the locale doing the classifying.

🦋 Return value 🦋

Returns true if the character is classified as lowercase, false otherwise. periodt. ✅

💖 Possible implementation 💖

Here's how it could look under the hood, no cap:

template<class CharT>
bool islower(CharT ch, const std::locale& loc)
{
    return
        std::use_facet<std::ctype<CharT>>(loc).is(std::ctype_base::lower, ch);
}

🌈 Example 🌈

Demonstrates the use of islower() with different locales (OS-specific). The original page also has a little // Run this code note. 🫶

#include <iostream>
#include <locale>

int main()
{
    const wchar_t c = L'\u03c0'; // GREEK SMALL LETTER PI

    std::locale loc1("C");
    std::cout << std::boolalpha
              << "islower('π', C locale) returned "
              << std::islower(c, loc1) << '\n'
              << "isupper('π', C locale) returned "
              << std::isupper(c, loc1) << '\n';

    std::locale loc2("en_US.UTF8");
    std::cout << "islower('π', Unicode locale) returned "
              << std::islower(c, loc2) << '\n'
              << "isupper('π', Unicode locale) returned "
              << std::isupper(c, loc2) << '\n';
}

🍓 Possible output 🍓

islower('π', C locale) returned false
isupper('π', C locale) returned false
islower('π', Unicode locale) returned true
isupper('π', Unicode locale) returned false

👑 See also 👑

• islower — checks if a character is lowercase (function).
• iswlower — checks if a wide character is lowercase (function).

and that's the whole page, bestie. source/version/date tea: http://cppreference.com, 2024.06.10, and std::islower(std::locale)(3). mwah 💋✨