Print a content of an utf16 file to the stdout.

utf16_to_utf8.c

/* Author: m039 <flam44 (at) gmail (dot) com> */

#include <stdio.h>

/*
 * Use the next command to test this snippet:
 *
 *   iconv -f utf8 -t utf16 utf8.txt -o utf16.txt
 *   ./utf16_to_utf8 utf16.txt > utf8.txt
 */

static FILE    *g_fp;
static char	g_buffer[512];	/* The buffer is too small for big files */

typedef unsigned int character;

void utf8(character ch, char **string) {
	char *src;

	if (*string == NULL) {
		return;
	}

	src = *string;

	if (ch <= 0x7f) {
		src[0] = ch;
		*string	+= 1;
	} else if (ch <= 0x0007ff) {
		src[0] = 0xc0 | (ch >>  6) & 0x1f;
		src[1] = 0x80 | (ch & 0x3f);
		*string	+= 2;
	} else if (ch <= 0x00ffff) {
		src[0] = 0xe0 | (ch >> 12) & 0x0f;
		src[1] = 0x80 | (ch >>  6) & 0x3f;
		src[2] = 0x80 | (ch & 0x3f);
		*string	+= 3;
	} else if (ch <= 0x10ffff) {
		src[0] = 0xf0 | (ch >> 18) & 0x07;
		src[1] = 0x80 | (ch >> 12) & 0x3f;
		src[2] = 0x80 | (ch >>  6) & 0x3f;
		src[3] = 0x80 | (ch & 0x3f);
		*string	+= 4;
	}
}

int fgetshort(FILE *fp) {
	int c1, c2;

	c1 = fgetc(fp);
	c2 = fgetc(fp);

	if ((c1 == EOF) || (c2 == EOF)) {
		return EOF;
	}

	return ((c2 << 8) | c1) & 0xffff;
}

int main(int argc, char **argv) {
	int c, surrogate;
	char *p = g_buffer;

	if (argc < 2) {
		fprintf(stderr, "Usage: ./utf16_to_utf8 <from>\n");
		return -1;
	}

	g_fp = fopen(argv[1], "r");
	if (g_fp == NULL) {
		perror(argv[1]);
		return -1;
	}

	while ((c = fgetshort(g_fp)) != EOF) {
		if ((c >= 0xd800) && (c <= 0xdbff)) {
			surrogate = (c - 0xd800) << 10;
		} else if ((c >= 0xdc00) && (c <= 0xdfff)) {
			surrogate |= c - 0xdc00;
			utf8(surrogate + 0x10000, &p);
		} else {
			utf8(c, &p);
		}
	}

	*p = 0;

	fclose(g_fp);
		
	puts(g_buffer);
}