\return Value of \c filename_local.
       \note Use the \c libcurl library, or the external binaries \c wget or \c curl to perform the download.
    **/
    inline char *load_network(const char *const url, char *const filename_local,
                              const unsigned int timeout, const bool try_fallback,
                              const char *const referer) {
      if (!url)
        throw CImgArgumentException("cimg::load_network(): Specified URL is (null).");
      if (!filename_local)
        throw CImgArgumentException("cimg::load_network(): Specified destination string is (null).");
      if (!network_mode())
        throw CImgIOException("cimg::load_network(): Loading files from network is disabled.");

      const char *const __ext = cimg::split_filename(url), *const _ext = (*__ext && __ext>url)?__ext - 1:__ext;
      CImg<char> ext = CImg<char>::string(_ext);
      std::FILE *file = 0;
      *filename_local = 0;
      if (ext._width>16 || !cimg::strncasecmp(ext,"cgi",3)) *ext = 0;
      else cimg::strwindows_reserved(ext);
      do {
        cimg_snprintf(filename_local,256,"%s%c%s%s",
                      cimg::temporary_path(),cimg_file_separator,cimg::filenamerand(),ext._data);
        if ((file=cimg::std_fopen(filename_local,"rb"))!=0) cimg::fclose(file);
      } while (file);

#ifdef cimg_use_curl
      const unsigned int omode = cimg::exception_mode();
      cimg::exception_mode(0);
      try {
        CURL *curl = 0;
        CURLcode res;
        curl = curl_easy_init();
        if (curl) {
          file = cimg::fopen(filename_local,"wb");
          curl_easy_setopt(curl,CURLOPT_URL,url);
          curl_easy_setopt(curl,CURLOPT_WRITEFUNCTION,0);
          curl_easy_setopt(curl,CURLOPT_WRITEDATA,file);
          curl_easy_setopt(curl,CURLOPT_SSL_VERIFYPEER,0L);
          curl_easy_setopt(curl,CURLOPT_SSL_VERIFYHOST,0L);
          curl_easy_setopt(curl,CURLOPT_FOLLOWLOCATION,1L);
          if (timeout) curl_easy_setopt(curl,CURLOPT_TIMEOUT,(long)timeout);
          if (std::strchr(url,'?')) curl_easy_setopt(curl,CURLOPT_HTTPGET,1L);
          if (referer) curl_easy_setopt(curl,CURLOPT_REFERER,referer);
          res = curl_easy_perform(curl);
          curl_easy_cleanup(curl);
          cimg::fseek(file,0,SEEK_END); // Check if file size is 0
          const cimg_ulong siz = cimg::ftell(file);
          cimg::fclose(file);
          if (siz>0 && res==CURLE_OK) {
            cimg::exception_mode(omode);
            return filename_local;
          } else std::remove(filename_local);
        }
      } catch (...) { }
      cimg::exception_mode(omode);
      if (!try_fallback) throw CImgIOException("cimg::load_network(): Failed to load file '%s' with libcurl.",url);
#endif

      CImg<char> command((unsigned int)std::strlen(url) + 512);
      cimg::unused(try_fallback);

      // Try with 'curl' first.
      if (timeout) {
        if (referer)
          cimg_snprintf(command,command._width,"\"%s\" -e %s -m %u -f --silent --compressed -o \"%s\" \"%s\"",
                        cimg::curl_path(),referer,timeout,filename_local,
                        CImg<char>::string(url)._system_strescape().data());
        else
          cimg_snprintf(command,command._width,"\"%s\" -m %u -f --silent --compressed -o \"%s\" \"%s\"",
                        cimg::curl_path(),timeout,filename_local,
                        CImg<char>::string(url)._system_strescape().data());
      } else {
        if (referer)
          cimg_snprintf(command,command._width,"\"%s\" -e %s -f --silent --compressed -o \"%s\" \"%s\"",
                        cimg::curl_path(),referer,filename_local,
                        CImg<char>::string(url)._system_strescape().data());
        else
          cimg_snprintf(command,command._width,"\"%s\" -f --silent --compressed -o \"%s\" \"%s\"",
                        cimg::curl_path(),filename_local,
                        CImg<char>::string(url)._system_strescape().data());
      }
      cimg::system(command, cimg::curl_path());

#if cimg_OS==2
      if (!(file=cimg::std_fopen(filename_local,"rb"))) {
        // Try with 'powershell' otherwise.
        if (timeout) {
          if (referer)
            cimg_snprintf(command,command._width,
                          "\"%s\" -NonInteractive -Command Invoke-WebRequest -Headers @{'Referer'='%s'} "
                          "-TimeoutSec %u -OutFile \"%s\" -Uri \"%s\"",
                          cimg::powershell_path(),referer,timeout,filename_local,
                          CImg<char>::string(url)._system_strescape().data());
          else
            cimg_snprintf(command,command._width,
                          "\"%s\" -NonInteractive -Command Invoke-WebRequest "
                          "-TimeoutSec %u -OutFile \"%s\" -Uri \"%s\"",
                          cimg::powershell_path(),timeout,filename_local,
                          CImg<char>::string(url)._system_strescape().data());
        } else {
          if (referer)
            cimg_snprintf(command,command._width,"\"%s\" -NonInteractive -Command Invoke-WebRequest "
                          "-Headers @{'Referer'='%s'} -OutFile \"%s\" -Uri \"%s\"",
                          cimg::powershell_path(),referer,filename_local,
                          CImg<char>::string(url)._system_strescape().data());
          else
            cimg_snprintf(command,command._width,"\"%s\" -NonInteractive -Command Invoke-WebRequest "
                          "-OutFile \"%s\" -Uri \"%s\"",
                          cimg::powershell_path(),filename_local,
                          CImg<char>::string(url)._system_strescape().data());
        }
        cimg::system(command, cimg::powershell_path());
      }
#endif

      if (!(file=cimg::std_fopen(filename_local,"rb"))) {

        // Try with 'wget' otherwise.
        if (timeout) {
          if (referer)
            cimg_snprintf(command,command._width,"\"%s\" --referer=%s -T %u -q -r -l 0 --no-cache -O \"%s\" \"%s\"",
                          cimg::wget_path(),referer,timeout,filename_local,
                          CImg<char>::string(url)._system_strescape().data());
          else
            cimg_snprintf(command,command._width,"\"%s\" -T %u -q -r -l 0 --no-cache -O \"%s\" \"%s\"",
                          cimg::wget_path(),timeout,filename_local,
                          CImg<char>::string(url)._system_strescape().data());
        } else {
          if (referer)
            cimg_snprintf(command,command._width,"\"%s\" --referer=%s -q -r -l 0 --no-cache -O \"%s\" \"%s\"",
                          cimg::wget_path(),referer,filename_local,
                          CImg<char>::string(url)._system_strescape().data());
          else
            cimg_snprintf(command,command._width,"\"%s\" -q -r -l 0 --no-cache -O \"%s\" \"%s\"",
                          cimg::wget_path(),filename_local,
                          CImg<char>::string(url)._system_strescape().data());
        }
        cimg::system(command, cimg::wget_path());

        if (!(file=cimg::std_fopen(filename_local,"rb")))
          throw CImgIOException("cimg::load_network(): Failed to load file '%s' with external commands "
#if cimg_OS==2
                                "'wget', 'curl', or 'powershell'.",url);
#else
                                "'wget' or 'curl'.",url);
#endif
        cimg::fclose(file);

        // Try gunzip it.
        cimg_snprintf(command,command._width,"%s.gz",filename_local);
        std::rename(filename_local,command);
        cimg_snprintf(command,command._width,"\"%s\" --quiet \"%s.gz\"",
                      gunzip_path(),filename_local);
        cimg::system(command, gunzip_path());
        file = cimg::std_fopen(filename_local,"rb");
        if (!file) {
          cimg_snprintf(command,command._width,"%s.gz",filename_local);
          std::rename(command,filename_local);
          file = cimg::std_fopen(filename_local,"rb");
        }
      }
      cimg::fseek(file,0,SEEK_END); // Check if file size is 0
      if (std::ftell(file)<=0)
        throw CImgIOException("cimg::load_network(): Failed to load URL '%s' with external commands "
                              "'wget' or 'curl'.",url);