C++ & Boost: encode/decode UTF-8

Question

I'm trying to do a very simple task: take a unicode-aware wstring and convert it to a string , encoded as UTF8 bytes, and then the opposite way around: take a string containing UTF8 bytes and convert it to unicode-aware wstring .

The problem is, I need it cross-platform and I need it work with Boost... and I just can't seem to figure a way to make it work. I've been toying with

• http://www.edobashira.com/2010/03/using-boost-code-facet-for-reading-utf8.html and
• http://www.boost.org/doc/libs/1_46_0/libs/serialization/doc/codecvt.html

Trying to convert the code to use stringstream / wstringstream instead of files of whatever, but nothing seems to work.

For instance, in Python it would look like so:

>>> u"שלום"
u'\u05e9\u05dc\u05d5\u05dd'
>>> u"שלום".encode("utf8")
'\xd7\xa9\xd7\x9c\xd7\x95\xd7\x9d'
>>> '\xd7\xa9\xd7\x9c\xd7\x95\xd7\x9d'.decode("utf8")
u'\u05e9\u05dc\u05d5\u05dd'

What I'm ultimately after is this:

wchar_t uchars[] = {0x5e9, 0x5dc, 0x5d5, 0x5dd, 0};
wstring ws(uchars);
string s = encode_utf8(ws); 
// s now holds "\xd7\xa9\xd7\x9c\xd7\x95\xd7\x9d"
wstring ws2 = decode_utf8(s);
// ws2 now holds {0x5e9, 0x5dc, 0x5d5, 0x5dd}

I really don't want to add another dependency on the ICU or something in that spirit... but to my understanding, it should be possible with Boost.

Some sample code would greatly be appreciated! Thanks

Answer 1

Thanks everyone, but ultimately I resorted to http://utfcpp.sourceforge.net/ -- it's a header-only library that's very lightweight and easy to use. I'm sharing a demo code here, should anyone find it useful:

inline void decode_utf8(const std::string& bytes, std::wstring& wstr)
{
    utf8::utf8to32(bytes.begin(), bytes.end(), std::back_inserter(wstr));
}
inline void encode_utf8(const std::wstring& wstr, std::string& bytes)
{
    utf8::utf32to8(wstr.begin(), wstr.end(), std::back_inserter(bytes));
}

Usage:

wstring ws(L"\u05e9\u05dc\u05d5\u05dd");
string s;
encode_utf8(ws, s);

Answer 2

There's already a boost link in the comments, but in the almost-standard C++0x, there is wstring_convert that does this

#include <iostream>
#include <string>
#include <locale>
#include <codecvt>
int main()
{
    wchar_t uchars[] = {0x5e9, 0x5dc, 0x5d5, 0x5dd, 0};
    std::wstring_convert<std::codecvt_utf8<wchar_t>> conv;
    std::string s = conv.to_bytes(uchars);
    std::wstring ws2 = conv.from_bytes(s);
    std::cout << std::boolalpha
              << (s == "\xd7\xa9\xd7\x9c\xd7\x95\xd7\x9d" ) << '\n'
              << (ws2 == uchars ) << '\n';
}

output when compiled with MS Visual Studio 2010 EE SP1 or with CLang++ 2.9

true 
true

Answer 3

Boost.Locale was released in Boost 1.48(November 15th, 2011) making it easier to convert from and to UTF8/16

Here are some convenient examples from the docs:

string utf8_string = to_utf<char>(latin1_string,"Latin1");
wstring wide_string = to_utf<wchar_t>(latin1_string,"Latin1");
string latin1_string = from_utf(wide_string,"Latin1");
string utf8_string2 = utf_to_utf<char>(wide_string);

Almost as easy as Python encoding/decoding :)

Note that Boost.Locale is not a header-only library.

Answer 4

For a drop-in replacement for std::string / std::wstring that handles utf8, see TINYUTF8 .

In combination with <codecvt> you can convert pretty much from/to every encoding from/to utf8, which you then handle through the above library.