#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <iconv.h>

int
iconv_convert(char **outstr, char *instr, const char *tocode, const char *fromcode)
{
	iconv_t cd;
	size_t ins;
	char   *in;
	size_t outbufsiz, outs;
	char   *outbuf, *out;
	size_t ret = 0, irr = 0;
	size_t idx = 0;
	size_t nconv = 0;
	char *str = NULL;

	cd = iconv_open(tocode, fromcode);
	if (cd == (iconv_t)-1)
		return -1;

	ins = strlen(instr);
	in = instr;

	outbufsiz = BUFSIZ;
	if ((out = outbuf = malloc(outbufsiz)) == NULL)
		return -1;

	while (ins > 0) {
		out = outbuf;
		outs = outbufsiz;

		ret = iconv(cd, &in, &ins, &out, &outs);
		nconv = outbufsiz - outs;
		if (ret == (size_t)-1) {
			switch (errno) {
			case EINVAL:
				goto err;
			case E2BIG:
				outbufsiz *= 2;
				out = realloc(outbuf, outbufsiz);
				if (!out)
					goto err;
				outbuf = out;
				break;
			default:
				goto err;
			}
		} else {
			irr += ret;
		}
		if (nconv > 0) {
			char *newstr;

			if (str == NULL)
				newstr = malloc(nconv + 1);
			else
				newstr = realloc(str, idx + nconv + 1);
			if (!newstr)
				goto err;
			str = newstr;
			memcpy(&str[idx], outbuf, nconv);
			idx += nconv;
		}
	}
	do {
		out = outbuf;
		outs = outbufsiz;

		ret = iconv(cd, NULL, NULL, &out, &outs);
		nconv = outbufsiz - outs;

		if (ret == (size_t)-1) {
			outbufsiz *= 2;
			out = realloc(outbuf, outbufsiz);
			if (!out)
				goto err;
			outbuf = out;
		} else {
			irr += ret;
		}
		if (nconv > 0) {
			char *newstr;

			if (str == NULL)
				newstr = malloc(nconv + 1);
			else
				newstr = realloc(str, idx + nconv + 1);
			if (!newstr)
				goto err;
			str = newstr;
			memcpy(&str[idx], outbuf, nconv);
			idx += nconv;
		}
	} while (ret == (size_t)-1);

	if (str == NULL)
		str = strdup("");
	else
		str[idx] = '\0';
	if (!str)
		goto err;

	*outstr = str;
	iconv_close(cd);
	return irr;

err:
	free(str);
	free(outbuf);

	iconv_close(cd);
	return -1;

}

int
main()
{
	char *buf;
	int ret;

	ret = iconv_convert(&buf, "こんにちはこんにちは！", "EUC-JP", "UTF-8");
	if (0 <= ret) {
		printf("%d: %s\n", ret, buf);
		free(buf);
	}

	return 1;
}