std::tolower(std::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

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

#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::wint_t)std::tolower(c, std::locale()) << '\n';
 
    std::cout << "in Unicode locale, tolower(" << (std::wint_t)c << ") = "
              << (std::wint_t)std::tolower(c, std::locale("en_US.utf8")) << '\n';
}

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

See also