[c++]u16Stringからstd::ifstream を作る

エンディアンで変わるのでお気をつけて

#include <istream>
#include <uchar.h>
#include <codecvt>
#include <string>

std::wstring& convertU16StringToWstring(std::wstring& ws, std::u16string& u16Str) {
	bool bigEndian;
	using namespace std;
	union
	{
		uint32_t b4;     /* 4byte    */
		uint8_t b1[4];  /* 1byte×4 */
	} bytes;
	bytes.b4 = 0x12345678;
	bigEndian = bytes.b1[0] == 12 ? true : false;
	std::u16string  utf16Str = u16Str;
	std::wstring_convert<codecvt_utf8<uint16_t>, uint16_t> utf8Conv;



	if (bigEndian)
	{
		wstring_convert<codecvt_utf16<wchar_t, 0x10ffff>, wchar_t> conv;
		ws = conv.from_bytes(
			reinterpret_cast<const char*> (&utf16Str[0]),
			reinterpret_cast<const char*> (&utf16Str[0] + utf16Str.size()));
	}
	else {
		wstring_convert<codecvt_utf16<wchar_t, 0x10ffff, little_endian>, wchar_t> conv;
		ws = conv.from_bytes(
			reinterpret_cast<const char*> (&utf16Str[0]),
			reinterpret_cast<const char*> (&utf16Str[0] + utf16Str.size()));
	}
	return ws;
}

std::ifstream fin;
fin.open(ws, ios::binary);