Std::tolower(std::locale) (3) Linux Manual Page

std::tolower(std::locale) – std::tolower(std::locale)

Synopsis

Defined in header<locale>

    template <class charT>

    charT tolower(charT ch, const locale &loc);

Converts the character ch to lowercase if possible, using the conversion rules specified by the given locale’s std::ctype facet.

Parameters

ch – character
loc – locale

Return value

Returns the lowercase form of ch if one is listed in the locale, otherwise return ch unchanged.

Notes

Only 1:1 character mapping can be performed by this function, e.g. the Greek uppercase letter ‘Σ’ has two lowercase forms, depending on the position in a word: ‘σ’ and ‘ς’. A call to std::tolower cannot be used to obtain the correct lowercase form in this case.

Possible implementation

  template< class charT >
  charT tolower( charT ch, const std::locale& loc ) {
      return std::use_facet<std::ctype<charT>>(loc).tolower(ch);
  }

Example

// Run this code

#include <iostream>

#include <cwctype>

#include <locale>
int main()

{
    wchar_t c = L'\u0190'; // Latin capital open E ('Ɛ')
    std::cout << std::hex << std::showbase;
    std::cout << "in the default locale, tolower(" << (std::wint_t)c << ") = "
              << std::tolower(c, std::locale()) << '\n';
    std::cout << "in Unicode locale, tolower(" << (std::wint_t)c << ") = "
              << std::tolower(c, std::locale("en_US.utf8")) << '\n';
}

Output:

in the default locale, tolower(0x190) = 0x190
in Unicode locale, tolower(0x190) = 0x25b

std::tolower(std::locale) (3) Linux Manual Page