iconv convert

iconv-test.cpp

#include <iostream>
#include <iconv.h>
#include <stdlib.h>
#include <string.h>
#include <sys/errno.h>
using namespace std;

char *
convert(const char *from_charset, const char *to_charset, const char *input) {
	size_t inleft, outleft, converted = 0;
	char *output, *outbuf, *tmp;
	const char *inbuf;
	size_t outlen;
	iconv_t cd;
	int errno;

	if ((cd = iconv_open(to_charset, from_charset)) == (iconv_t) -1)
		return NULL;

	inleft = strlen(input);
	inbuf = input;

	/* we'll start off allocating an output buffer which is the same size
	 * as our input buffer. */
	outlen = inleft;

	/* we allocate 4 bytes more than what we need for nul-termination... */
	if (!(output = (char*) malloc(outlen + 4))) {
		iconv_close(cd);
		return NULL;
	}

	do {
		errno = 0;
		outbuf = output + converted;
		outleft = outlen - converted;

		converted = iconv(cd, (char **) &inbuf, &inleft, &outbuf, &outleft);
		if (converted != (size_t) -1 || errno == EINVAL) {
			/*
			 * EINVAL  An  incomplete  multibyte sequence has been encoun­-
			 *         tered in the input.
			 *
			 * We'll just truncate it and ignore it.
			 */
			break;
		}

		if (errno != E2BIG) {
			/*
			 * EILSEQ An invalid multibyte sequence has been  encountered
			 *        in the input.
			 *
			 * Bad input, we can't really recover from this.
			 */
			iconv_close(cd);
			free(output);
			return NULL;
		}

		/*
		 * E2BIG   There is not sufficient room at *outbuf.
		 *
		 * We just need to grow our outbuffer and try again.
		 */

		converted = outbuf - output;
		outlen += inleft * 2 + 8;

		if (!(tmp = (char*) realloc(output, outlen + 4))) {
			iconv_close(cd);
			free(output);
			return NULL;
		}

		output = tmp;
		outbuf = output + converted;
	} while (1);

	/* flush the iconv conversion */
	iconv(cd, NULL, NULL, &outbuf, &outleft);
	iconv_close(cd);

	/* Note: not all charsets can be nul-terminated with a single
	 * nul byte. UCS2, for example, needs 2 nul bytes and UCS4
	 * needs 4. I hope that 4 nul bytes is enough to terminate all
	 * multibyte charsets? */

	/* nul-terminate the string */
	memset(outbuf, 0, 4);

	return output;
}

int main() {

	string input = string("Test æøå a");
	char* outoutBuffer;
	outoutBuffer = convert("UTF-8", "ISO-8859-1", input.c_str());
	string output = string(outoutBuffer);
	cout << input << endl;
	cout << output << endl;
	return 0;
}

Hello, thanks a lot for this nice example, the cleaner I found so far for iconv !
Just a question with the realloc. I'm not very fluent with C and I found that realloc could be tricky in some case:
https://stackoverflow.com/questions/44789295/correct-use-of-realloc
Do you think it worth it to use this double pointer or is it too much ?

Thank you for your code this help me for my project c ++ to print in a terminal TM T20II epson ticket