getpeername()的注释
getpeername()函数用于从端口s中获取与它捆绑的端口名，并把它存放在sockaddr类型的name结构中。它适用于数据报或流类套接口。
返回值：
若无错误发生，getpeername()返回零。否则的话，返回SOCKET_ERROR，应用程序可通过WSAGetLastError()来获取相应的错误代码。
错误代码：
WSANOTINITIALISED：在使用此API之前应首先成功地调用WSAStartup()。
WSAENETDOWN：WINDOWS套接口实现检测到网络子系统失效。
WSAEFAULT：namelen参数不够大。
WSAEINPROGRESS：一个阻塞的WINDOWS套接口调用正在运行中。
WSAENOTCONN 套接口未连接。
WSAENOTSOCK：描述字不是一个套接口。
参见：
bind(), socket(), getsockname().
Linux system
Name
getpeername - get name of connected peer socket
Synopsis
#include <sys/socket.h>
int getpeername(int s, struct sockaddr *name, socklen_t *namelen);
Description
getpeername() returns the name of the peer connected to socket s. The namelen parameter should be initialized to indicate the amount of space pointed to by name. On return it contains the actual size of the name returned (in bytes). The name is truncated if the buffer provided is too small.
Return Value
On success, zero is returned. On error, -1 is returned, and errno is set appropriately.
Errors
EBADF
The argument s is not a valid descriptor.
EFAULT
The name parameter points to memory not in a valid part of the process address space.
EINVAL
namelen is invalid (e.g., is negative).
ENOBUFS
Insufficient resources were available in the system to perform the operation.
ENOTCONN
The socket is not connected.
ENOTSOCK
The argument s is a file, not a socket.
Conforming to
SVr4, 4.4BSD (the getpeername() function call first appeared in 4.2BSD), POSIX.1-2001.
Note
The third argument of getpeername() is in reality an int * (and this is what 4.x BSD and libc4 and libc5 have). Some POSIX confusion resulted in the present socklen_t, also used by glibc. See also accept(2).
