CODEWITHSUNDEEP
c++tolower
Yavuz
Yavuz

Reputation: 1393

tolower() is not working for Ü,Ö in c++

When I tried tolower() with non english charecters in c++ it's not working normally. I searched that issue and I came across something about locale but I am not sure about best solution of that.

My sample code is below:

printf("%c ",tolower('Ü'));

Upvotes: 4

Views: 1175

Answers (2)

Bart van Ingen Schenau
Bart van Ingen Schenau

Reputation: 15768

Unfortunately, the standard C++ library does not have sufficient support for changing the case of all possible non-English characters (in so far as those characters that have case variants at all). This limitation is caused by the fact that the C++ standard assumes that a single character and its case variants occupy exactly one char object (or wchar_t object for wide characters) and for non-English characters that is not guaranteed to be true (also depending on how the characters are coded).

If your environment uses a single-byte encoding for the relevant characters, this might give you what you want:

std::cout << std::tolower('Ü', locale());

With wide characters, you will probably have more luck:

std::wcout << std::tolower(L'Ü', locale());

but even that won't give the correct result for toupper(L'ß'), which would be the two-character sequence L"SS").

If you need support for all characters, take a look at the ICU library, in particular the part about case mappings

Upvotes: 6

Konrad Rudolph
Konrad Rudolph

Reputation: 545905

Like Bart has shown, C++ simply doesn’t like multi-byte encodings. Luckily, you can use Boost.Local to solve this without too much hassle. Here’s a simple example:

#include <iostream>
#include <locale>
#include <boost/locale.hpp>

int main() {
    boost::locale::generator gen;
    std::locale loc = gen("en_US.UTF-8");
    std::string line;
    while (std::getline(std::cin, line))
        std::cout << boost::locale::to_lower(line, loc) << '\n';
}

To compile, we need to link to the Boost.Locale library:

g++ -lboost_locale lower.cpp -o lower

And when we execute it, we get the following:

$ ./main <<< 'ICH HÄTTE GERNE EINEN SÜßEN HASEN'
ich hätte gerne einen süßen hasen

Upvotes: 3

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