Converting between encodings is easy with C++11 and most compilers are able to deal with it in a cross-platform manner through <codecvt> and <locale> headers.
#include <iostream>
#include <codecvt>
#include <locale>
#include <string>
using namespace std;
int main() {
// converts between wstring and utf8 string
wstring_convert<codecvt_utf8_utf16<wchar_t>> wchar_to_utf8;
// converts between u16string and utf8 string
wstring_convert<codecvt_utf8_utf16<char16_t>, char16_t> utf16_to_utf8;
wstring wstr = L"foobar";
string utf8str = wchar_to_utf8.to_bytes(wstr);
wstring wstr2 = wchar_to_utf8.from_bytes(utf8str);
wcout << wstr << endl;
cout << utf8str << endl;
wcout << wstr2 << endl;
u16string u16str = u"foobar";
string utf8str2 = utf16_to_utf8.to_bytes(u16str);
u16string u16str2 = utf16_to_utf8.from_bytes(utf8str2);
return 0;
}Mind that Visual Studio 2015 provides supports for these conversion but a bug in their library implementation requires to use a different template for wstring_convert when dealing with char16_t:
using utf16_char = unsigned short;
wstring_convert<codecvt_utf8_utf16<utf16_char>, utf16_char> conv_utf8_utf16;
void strings::utf16_to_utf8(const std::u16string& utf16, std::string& utf8)
{
std::basic_string<utf16_char> tmp;
tmp.resize(utf16.length());
std::copy(utf16.begin(), utf16.end(), tmp.begin());
utf8 = conv_utf8_utf16.to_bytes(tmp);
}
void strings::utf8_to_utf16(const std::string& utf8, std::u16string& utf16)
{
std::basic_string<utf16_char> tmp = conv_utf8_utf16.from_bytes(utf8);
utf16.clear();
utf16.resize(tmp.length());
std::copy(tmp.begin(), tmp.end(), utf16.begin());
}