UTF File to UTF-8 in std::string in C++ on Windows

ReadUtfFile.cpp

// Reading ASCII, UTF-8, UTF-16LE, UTF-16BE with auto BOM detection using C++11 on Windows platform
// Code tested on Microsoft Visual Studio 2013 on Windows 7
// Part of the code is referencing http://cfc.kizzx2.com/index.php/reading-a-unicode-utf16-file-in-windows-c/

#include <stdio.h>
#include <tchar.h>
#include <string>
#include <fstream>
#include <sstream>
#include <locale>
#include <codecvt>
#include <iostream>
#include <io.h>
#include <fcntl.h>

#define TEXT_FILE_PATH      "D:\\test.txt"
#define ENCODING_ASCII      0
#define ENCODING_UTF8       1
#define ENCODING_UTF16LE    2
#define ENCODING_UTF16BE    3

std::string readFile(std::string path)
{
	std::string result;
	std::ifstream ifs(path.c_str(), std::ios::binary);
	std::stringstream ss;
	int encoding = ENCODING_ASCII;

	if (!ifs.is_open()) {
		// Unable to read file
		result.clear();
		return result;
	}
	else if (ifs.eof()) {
		result.clear();
	}
	else {
		int ch1 = ifs.get();
		int ch2 = ifs.get();
		if (ch1 == 0xff && ch2 == 0xfe) {
			// The file contains UTF-16LE BOM
			encoding = ENCODING_UTF16LE;
		}
		else if (ch1 == 0xfe && ch2 == 0xff) {
			// The file contains UTF-16BE BOM
			encoding = ENCODING_UTF16BE;
		}
		else {
			int ch3 = ifs.get();
			if (ch1 == 0xef && ch2 == 0xbb && ch3 == 0xbf) {
				// The file contains UTF-8 BOM
				encoding = ENCODING_UTF8;
			}
			else {
				// The file does not have BOM
				encoding = ENCODING_ASCII;
				ifs.seekg(0);
			}
		}
	}
	ss << ifs.rdbuf() << '\0';
	if (encoding == ENCODING_UTF16LE) {
		std::wstring_convert<std::codecvt_utf8_utf16<wchar_t>> utfconv;
		result = utfconv.to_bytes(std::wstring((wchar_t *)ss.str().c_str()));
	}
	else if (encoding == ENCODING_UTF16BE) {
		std::string src = ss.str();
		std::string dst = src;
		// Using Windows API
		_swab(&src[0u], &dst[0u], src.size() + 1);
		std::wstring_convert<std::codecvt_utf8_utf16<wchar_t>> utfconv;
		result = utfconv.to_bytes(std::wstring((wchar_t *)dst.c_str()));
	}
	else if (encoding == ENCODING_UTF8) {
		result = ss.str();
	}
	else {
		result = ss.str();
	}
	return result;
}

int _tmain(int argc, _TCHAR* argv[])
{
	std::string path = TEXT_FILE_PATH;
	std::string utf8Content = readFile(path);
	std::wstring_convert<std::codecvt_utf8_utf16<wchar_t>> utfconv;
	std::wstring utf16LeContent = utfconv.from_bytes(utf8Content);
	_setmode(_fileno(stdout), _O_U8TEXT);
	std::wcout << utf16LeContent << std::endl;
	return 0;
}

What if the file is located on a path with Unicode chars? You could encode that as utf-8 for the input parameter, but I doubt ifstream can handle that.

That's truth that ifstream will not be able to handle path with Unicode character. This code is mainly demonstrate reading the file content actually. Thanks for your note.