std::tolower(std::locale)

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

#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

toupper(std::locale)	converts a character to uppercase using the ctype facet of a locale (function template)
tolower	converts a character to lowercase (function)
towlower	converts a wide character to lowercase (function)