std::tolower(std::locale) (3) - Linux Man Pages

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


std::tolower(std::locale) - 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.


ch - character
loc - locale

Return value

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


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);


// 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';


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

See also

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