基于libcurl库实现从ftp服务器上下载文件包括断点续传

<!-- Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al. SPDX-License-Identifier: curl --> # include Public include files for libcurl, external users. They're all placed in the curl subdirectory here for better fit in any kind of environment. You must include files from here using... #include <curl/curl.h> ... style and point the compiler's include path to the directory holding the curl subdirectory. It makes it more likely to survive future modifications. The public curl include files can be shared freely between different platforms and different architectures.