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

static int fails_iteratively_with_reset(char *input)
{
    iconv_t cd = iconv_open("UTF-8", "UTF-16");
    if (cd == (iconv_t)-1)
        return -1;

    char output[6]; // UTF-8-BOM (possibly) + "23" + NUL
    char *inbuf = input;
    size_t inbytesleft = 4;
    char *outbuf = output;
    size_t outbytesleft = 6;

    size_t res = iconv(cd, &inbuf, &inbytesleft, &outbuf, &outbytesleft);
    if (res == (size_t)-1) {
        iconv_close(cd);
        return -1;
    }
    iconv(cd, NULL, NULL, NULL, NULL);

    inbytesleft = 6 - (4 - inbytesleft);
    res = iconv(cd, &inbuf, &inbytesleft, &outbuf, &outbytesleft);
    iconv_close(cd);
    if (res == (size_t)-1)
        return -1;
    *outbuf = 0;

    /* remove UTF-8 BOM if present (unlikely) */
    int offset = 0;
    if ((outbuf - output >= 3) && !memcmp(output, "\xef\xbb\xbf", 3))
        offset = 3;

    if (!memcmp(output + offset, "23", 3))
        return 0; /* success, conversion works iteratively */
    else
        return 1; /* wrong result */ 
}

int main(void)
{
    unsigned words[] = { 0xfeff /* BOM */, 0x32 /* 2 */, 0x33 /* 3 */};
    char little[6];
    char big[6];
    
    for(int i = 0; i < 6; i += 2) {
        unsigned w = words[i/2];
        big[i] = little[i+1] = (char) (w >> 8);
        big[i+1] = little[i] = w & 0xff;
    }
    
    switch(fails_iteratively_with_reset(little)) {
    case 0: printf("Conversion works iteratively (little-endian).\n");
            break;
    case 1: printf("Iterative conversion fails with reset (little-endian).\n");
            break;
    case -1: 
    default: printf("Test error (little-endian).");
             break;
    }

    switch(fails_iteratively_with_reset(big)) {
    case 0: printf("Conversion works iteratively (big-endian).\n");
            break;
    case 1: printf("Iterative conversion fails with reset (big-endian).\n");
            break;
    case -1: 
    default: printf("Test error (big-endian).");
             break;
    }
}