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# std::ctype::tolower, std::ctype::do_tolower

From cppreference.com
< cpp‎ | locale‎ | ctype

Defined in header `<locale>` |  |
public: CharT tolower( CharT c ) const; | (1) |
public: const CharT* tolower( CharT* beg, const CharT* end ) const; | (2) |
protected: virtual CharT do_tolower( CharT c ) const; | (3) |
protected: virtual const CharT* do_tolower( CharT* beg, const CharT* end ) const; | (4) |

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.

### [edit] 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

### [edit] Return value

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

### [edit] 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.

### [edit] 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!'

### [edit] See also

toupper | invokes `do_toupper` (public member function) [edit]
tolower | converts a character to lowercase (function) [edit]
towlower | converts a wide character to lowercase (function) [edit]

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