How to print UTF-8 strings to std::cout on Windows?

c++, encoding, utf-8, windows

Solution

The problem is not `std::cout` but the windows console. Using C-stdio you will get the `ü` with `fputs( "\xc3\xbc", stdout );` after setting the UTF-8 codepage (either using `SetConsoleOutputCP` or `chcp`) and setting a Unicode supporting font in cmd's settings (Consolas should support over 2000 characters and there are registry hacks to add more capable fonts to cmd).

If you output one byte after the other with `putc('\xc3'); putc('\xbc');` you will get the double tofu as the console gets them interpreted separately as illegal characters. This is probably what the C++ streams do.

See UTF-8 output on Windows console for a lenghty discussion.

For my own project, I finally implemented a `std::stringbuf` doing the conversion to Windows-1252. I you really need full Unicode output, this will not really help you, however.

An alternative approach would be overwriting `cout`'s streambuf, using `fputs` for the actual output:

#include <iostream>
#include <sstream>

#include <Windows.h>

class MBuf: public std::stringbuf {
public:
    int sync() {
        fputs( str().c_str(), stdout );
        str( "" );
        return 0;
    }
};

int main() {
    SetConsoleOutputCP( CP_UTF8 );
    setvbuf( stdout, nullptr, _IONBF, 0 );
    MBuf buf;
    std::cout.rdbuf( &buf );
    std::cout << u8"Greek: αβγδ\n" << std::flush;
}

I turned off output buffering here to prevent it to interfere with unfinished UTF-8 byte sequences.

Problem

I'm writing a cross-platform application in C++. All strings are UTF-8-encoded internally. Consider the following simplified code: ``` #include <string> #include <iostream> int main() { std::string test = u8"Greek: αβγδ; German: Übergrößenträger"; std::cout << test; return 0; } ``` On Unix systems, `std::cout` expects 8-bit strings to be UTF-8-encoded, so this code works fine. On Windows, however, `std::cout` expects 8-bit strings to be in Latin-1 or a similar non-Unicode format (depending on the codepage). This leads to the following output: Greek: ╬▒╬▓╬│╬┤; German: ├£bergr├Â├ƒentr├ñger What can I do to make `std::cout` interpret 8-bit strings as UTF-8 on Windows? This is what I tried: ``` #include <string> #include <iostream> #include <io.h> #include <fcntl.h> int main() { _setmode(_fileno(stdout), _O_U8TEXT); std::string test = u8"Greek: αβγδ; German: Übergrößenträger"; std::cout << test; return 0; } ``` I was hoping that `_setmode` would do the trick. However, this results in the following assertion error in the line that calls `operator<<`: Microsoft Visual C++ Runtime Library Debug Assertion Failed! Program: d:\visual studio 2015\Projects\utf8test\Debug\utf8test.exe File: minkernel\crts\ucrt\src\appcrt\stdio\fputc.cpp Line: 47 Expression: ( (_Stream.is_string_backed()) || (fn = _fileno(_Stream.public_stream()), ((_textmode_safe(fn) == __crt_lowio_text_mode::ansi) && !_tm_unicode_safe(fn)))) For information on how your program can cause an assertion failure, see the Visual C++ documentation on asserts.

Original source

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