利用curl计算网络文件大小

     double zipsize = ;
     CURL *handle = curl_easy_init();
     curl_easy_setopt(handle, CURLOPT_URL, url);
     curl_easy_setopt(handle, CURLOPT_HEADER, );   //只需要header头
     curl_easy_setopt(handle, CURLOPT_NOBODY, );   //不需要body

     if (curl_easy_perform(handle) == CURLE_OK)
     {
      curl_easy_getinfo(handle, CURLINFO_CONTENT_LENGTH_DOWNLOAD, &zipsize);
         packageBytesTotal = (int)((zipsize / ) + 0.5);
         std::cout << "当前要加载的包大小为: " << packageBytesTotal << "KB" << std::endl;
     }
     curl_easy_cleanup(handle);