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

 #include <iconv.h>

int encoding_convert(const char *tocode, const char *fromcode,
                           char *inbuf, size_t *inbytesleft, char *outbuf, size_t *outbytesleft)
{
  iconv_t cd = 0;
  char *in_buf = inbuf;
  char *out_buf = outbuf;
  size_t len = *outbytesleft;
  size_t nonreversible_characters = -1;

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

  nonreversible_characters = iconv(cd, &in_buf, inbytesleft, &outbuf, outbytesleft);
  if (nonreversible_characters < 0) {
    return -1;
  }
  iconv_close(cd);

  len -= *outbytesleft;
  out_buf[len] = '\0';
  return (int)(len);
}

int main(int argc, char *argv[])
{
  char  s[] = "中国人哈哈哈";
  char *utf8 = s;
  size_t  s_len = strlen(s);
  char buf[512];
  char *gb2312 = buf;
  size_t len = 512;

  int aa = encoding_convert("GB2312//IGNORE","UTF-8", utf8 , &s_len, gb2312, &len) ;
  if (aa > 0) {
      printf("%d  %d %d\n",  aa, (int)s_len, 512 - (int)len);
  }

   return 0;
}