Libcurl

snprintf(cmd, sizeof(cmd), "curl -T \"%s\" -u \"%s:%s\" ftp://%s:%d/%s/ -s -S -m %d --connect-timeout %d --ftp-create-dirs 2>&1",
        src_file, userid, passwd,
        ipaddr, port, dst_dir,
        timeout, conn_timeout);

fp = popen(cmd, "r");
if(fp == NULL) {
    LOG_ERR("%s:: popen() fail: errno=%d(%s)\n",
            _func_, errno, strerror(errno));
    return -1;
}
while(fgets(buff, sizeof(buff), fp) != NULL) {
    LOG_ERR("%s:: ftp upload error: err=%s", _func_, buff);
    success_flag = 0;
    break;
}
pclose(fp);

/* This is the callback executed when a new threads starts */
static void *pull_one_url(void *url)
{
  CURL *curl;

  curl = curl_easy_init();
  curl_easy_setopt(curl, CURLOPT_URL, url);
  curl_easy_perform(curl); /* ignores error */ 
  curl_easy_cleanup(curl);

  return NULL;
}

/* ... */

/* This is the main loop that creates `NUMT` threads for parallel fetching */
for(i=0; i< NUMT; i++) {
    error = pthread_create(&tid[i],
                           NULL, /* default attributes please */ 
                           pull_one_url,
                           (void *)urls[i]);
  /* ... */
}