A filter for convert utf8 to utf16 in windows.

utf8to16.c

// Use mingw in windows
// gcc -O2 -o utf8.exe utf8to16.c
#include <stdio.h>
#include <fcntl.h>  
#include <io.h>
#include <wchar.h>

static const char trailingBytesForUTF8[256] = {
	0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
	0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
	0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
	0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
	0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
	0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
	1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
	2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2, 3,3,3,3,3,3,3,3,4,4,4,4,5,5,5,5
};

	
static const unsigned long offsetsFromUTF8[6] = {
	0x00000000UL, 0x00003080UL, 0x000E2080UL, 
	0x03C82080UL, 0xFA082080UL, 0x82082080UL 
};


#define UNI_SHIFT 10
#define UNI_BASE 0x0010000
#define UNI_MASK 0x3FF
#define UNI_SUR_HIGH_START 0xD800
#define UNI_SUR_LOW_START 0xDC00

int
main() {
	int c;
	_setmode(_fileno(stdout), _O_WTEXT);
	while ((c=fgetc(stdin)) >= 0) {
		unsigned long ch = 0;
		int extra = trailingBytesForUTF8[c];
#define READBYTE() ch += c; ch <<= 6; if ((c=fgetc(stdin)) < 0) return 1;
		switch (extra) {
		case 5: READBYTE();
		case 4: READBYTE();
		case 3: READBYTE();
		case 2: READBYTE();
		case 1: READBYTE();
		case 0: ch += c;
		}
		ch -= offsetsFromUTF8[extra];
		if (ch <= 0xffff) {
			wprintf(L"%lc", ch);
		} else {
			ch -= UNI_BASE;
			wprintf(L"%lc%lc", (ch >> UNI_SHIFT) + UNI_SUR_HIGH_START,
				(ch & UNI_MASK) + UNI_SUR_LOW_START);
		}
	}
	return 0;
}