MinGW wifstream

main.cpp

#include <ext/stdio_filebuf.h>	// fstream (all sorts of IO stuff) + stdio_filebuf (=streambuf)
#include <fcntl.h>	// _O_RDONLY
#include <iostream>	// cout

int main(){
	__gnu_cxx::stdio_filebuf<char> wfile_buf(_wopen(L"D:\\...\\の.txt", _O_RDONLY), std::ios_base::in);
	std::istream wfile_stream(&wfile_buf);
	wfile_stream.seekg(0, std::ios_base::end);
	std::cout << wfile_stream.tellg();
	return 0;
}