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

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';
}

Output:

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

Language
Standard Library Headers
Freestanding and hosted implementations
Named requirements
Language support library
Concepts library (C++20)
Diagnostics library
Utilities library
Strings library
Containers library
Iterators library
Ranges library (C++20)
Algorithms library
Numerics library
Input/output library
Localizations library
Regular expressions library (C++11)
Atomic operations library (C++11)
Thread support library (C++11)
Filesystem library (C++17)
Technical Specifications