The getpeername function returns the address of the socket that
socket is connected to; it stores the address in the memory space
specified by addr and length-ptr. It stores the length of
the address in *length-ptr.
See Socket Addresses, for information about the format of the
address. In some operating systems, getpeername works only for
sockets in the Internet domain.
The return value is 0 on success and -1 on error. The
following errno error conditions are defined for this function:
EBADF- The argument socket is not a valid file descriptor.
ENOTSOCK- The descriptor socket is not a socket.
ENOTCONN- The socket socket is not connected.
ENOBUFS- There are not enough internal buffers available.
