fd is the file descriptor, a pointer to the file. For this example, use the following

fd是文件描述符，是指向文件的一个指针。

youdao

If the optional fd parameter is specified, it is interpreted as an integral file descriptor to be sent over the stream.

如果指定了可选参数fd，它将被作为一个文件描述符通过流传送。

youdao

If the optional fd parameter is specified, it is interpreted as an integral file descriptor to be sent over the stream.

如果指定了可选参数fd，它将被作为一个文件描述符通过流传送。

youdao