C언어 iconv_open() Invalid argument error

int main()
{
    //iconv_t cd = iconv_open("UNICODE","UTF-8");
    iconv_t cd = iconv_open("UTF-8","EUC-KR");
    if( cd == (iconv_t)-1)
    {
        //printf("iconv_open error\n");
        perror("iconv_open error");
        return 0;
    }
 
    //char inbuff[BUFF_SIZE] = "HELLO world";
    char inbuff[BUFF_SIZE] = "한글";
    int inbufsize = sizeof(inbuff);
 
    char outbuff[BUFF_SIZE];
    int outbuffsize = sizeof(outbuff);
    memset(outbuff, 0 , outbuffsize);
 
    size_t readbyte = strlen(inbuff);
    size_t writebyte = sizeof(outbuff);
    char* in = inbuff;
    char* out = outbuff;
 
    printf("readBytes:%d writeBytes:%d\n",readbyte,writebyte);
 
    printf("%s\n",inbuff);
    if( IsUTF8Encode(inbuff) )
    {
        printf("utf-8\n");
    }
    else
    {
        printf("no utf-8\n");
    }
 
    if( iconv(cd, &in, &readbyte, &out, &writebyte) == -1)
    {
        printf("failed to iconv error\n");
    }
    else
    {
        int idx;
        printf("in:%x out:%x\n",in,out);
        printf("readBytes:%d writeBytes:%d\n",readbyte,writebyte);
        for(idx=0;idx<BUFF_SIZE;idx++)
        {
            printf("%03d %c %x\t\t", idx, inbuff[idx], inbuff[idx]);
            printf("%03d %c %x\n", idx, outbuff[idx], outbuff[idx]);
        }
 
        outbuff[writebyte] = '\0';
 
        if( IsUTF8Encode(outbuff) )
        {
            printf("utf-8\n");
        }
        else
        {
            printf("no utf-8\n");
        }
        printf("%s\n",outbuff);
    }
 
    iconv_close( cd );
    return 0;
}