c++ - socket编程，什么是FD和SD

Question

我正在编写一个 SSL 套接字，我多次看到名称中带有 FD 或 SD 的东西(变量名、函数...)。例如，OpenSSL 提供了功能:

int fd = SSL_get_fd(...);

在许多教程中(here、here 和 here)，使用的是:

int sd = socket(...);

谁能解释一下，FD和SD分别代表什么？

谢谢

Answer 1

SSL_get_fd :

SSL_get_fd() returns the file descriptor

File Descriptor :

In Unix and related computers operating systems, a file descriptor (FD, less frequently fildes) is an abstract indicator used to access a file or other input/output resource, such as a pipe or network connection. File descriptors are part of the POSIX application programming interface. A file descriptor is a non-negative integer, represented in C programming language as the type int.

wfd, rfd 分别代表 write-FD 和 read-FD。 sd 不是标准的名字，但它可能代表“套接字文件描述符”，即。一个FD对应一个socket。来自同一个 SSL_get_fd 页面:

fd will typically be the socket file descriptor of a network connection