std::ctype<CharT>::tolower, std::ctype<CharT>::do_tolower

< cpp‎ | locale‎ | ctype
Defined in header <locale>
CharT tolower( CharT c ) const;
const CharT* tolower( CharT* beg, const CharT* end ) const;
virtual CharT do_tolower( CharT c ) const;
virtual const CharT* do_tolower( CharT* beg, const CharT* end ) const;
1,2) public member function, calls the protected virtual member function do_tolower of the most derived class.
3) Converts the character c to lower case if a lower case form is defined by this locale.
4) For every character in the character array [beg, end), for which a lower case form exists, replaces the character with that lower case form.


c - character to convert
beg - pointer to the first character in an array of characters to convert
end - one past the end pointer for the array of characters to convert

Return value

1,3) lower case character or c if no lower case form is listed by this locale.
2,4) end.


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 do_tolower cannot be used to obtain the correct lowercase form in this case.


#include <locale>
#include <iostream>
void try_lower(const std::ctype<wchar_t>& f, wchar_t c)
    wchar_t up = f.tolower(c);
    if (up != c) {
        std::wcout << "Lower case form of \'" << c << "' is " << up << '\n';
    } else {
        std::wcout << '\'' << c << "' has no lower case form\n";
int main()
    std::wcout << "In US English UTF-8 locale:\n";
    auto& f = std::use_facet<std::ctype<wchar_t>>(std::locale());
    try_lower(f, L'Σ');
    try_lower(f, L'Ɛ');
    try_lower(f, L'A');
    std::wstring str = L"HELLo, wORLD!";
    std::wcout << "Lowercase form of the string '" << str << "' is ";
    f.tolower(&str[0], &str[0] + str.size());
    std::wcout << "'" << str << "'\n";


In US English UTF-8 locale:
Lower case form of 'Σ' is σ
Lower case form of 'Ɛ' is ɛ
Lower case form of 'A' is a
Lowercase form of the string 'HELLo, wORLD!' is 'hello, world!'

See also

invokes do_toupper
(public member function)
converts a character to lowercase
converts a wide character to lowercase