Convert string to wstring to write to file with utf-16 encoding

utf-16_encoder.cpp

// Windows version
#include <string>
#include <iostream>
#include <fstream>
#include <locale>
#include <codecvt>
#include <Windows.h>

std::wstring decode(const std::string &str, int codePage = GetACP())
{
	if (str.empty()) return std::wstring();
	int size_needed = MultiByteToWideChar(codePage, 0, &str[0], (int)str.size(), NULL, 0);
	std::wstring wstrTo(size_needed, 0);
	MultiByteToWideChar(codePage, 0, &str[0], (int)str.size(), &wstrTo[0], size_needed);
	return wstrTo;
}

std::string encode(const std::wstring &wstr, int codePage = GetACP())
{
	if (wstr.empty()) return std::string();
	int size_needed = WideCharToMultiByte(codePage, 0, &wstr[0], (int)wstr.size(), NULL, 0, NULL, NULL);
	std::string strTo(size_needed, 0);
	WideCharToMultiByte(codePage, 0, &wstr[0], (int)wstr.size(), &strTo[0], size_needed, NULL, NULL);
	return strTo;
}

int _tmain(int argc, _TCHAR* argv[])
{
	std::wofstream fout("text-utf16.txt", std::ios::binary);
	const unsigned long MaxCode = 0x10ffff;
	const std::codecvt_mode Mode = (std::codecvt_mode)(std::generate_header | std::little_endian);
	std::locale utf16_locale(fout.getloc(), new std::codecvt_utf16<wchar_t, MaxCode, Mode>);
	fout.imbue(utf16_locale);
	
	fout << decode("ßz水");
	
	// You can also encode to other codePage
	std::ofstream fout2("text-858.txt", std::ios::binary);
	fout2 << encode(decode("ßz水"));
	
}


// Linux Version
#include <string>
#include <iostream>
#include <fstream>
#include <locale>
#include <codecvt>

int main() {
    char s[] = "ßz水";
    std::wstring_convert<std::codecvt_utf8_utf16<wchar_t>> converter;
    std::wstring wide = converter.from_bytes(s);
    std::wofstream fout("text.txt", std::ios::binary);
    const unsigned long MaxCode = 0x10ffff;
    const std::codecvt_mode Mode = std::generate_header;
    std::locale utf16_locale(fout.getloc(), new std::codecvt_utf16<wchar_t, MaxCode, Mode>);
    fout.imbue(utf16_locale);
    fout << wide;
}

Windows Version