Std::ctype::tolower,std::ctype::do_tolower (3) Linux Manual Page

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

Synopsis

Defined in header<locale>

    public : (1)

                 CharT tolower(CharT c) const;

public:
(2)

    const CharT *tolower(CharT *beg, const CharT *end) const;

protected:
(3)

    virtual CharT do_tolower(CharT c) const;

protected:
(4)

    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.

Parameters

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.

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

Example

// Run this code

#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::locale::global(std::locale("en_US.utf8"));
    std::wcout.imbue(std::locale());
    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";
}

Output:

  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!’

std::ctype::tolower,std::ctype::do_tolower (3) Linux Manual Page