Taken from the original at http://www.ecst.csuchico.edu/~beej/guide/net/ ... see end of writeup for Copyright statement.
getpeername()--Who are you?
This function is so easy.
It's so easy, I almost didn't give it it's own section. But here it is anyway.
The function getpeername() will tell you who is at the other end of a connected stream socket. The synopsis:
int getpeername(int sockfd, struct sockaddr *addr, int *addrlen);
sockfd is the descriptor of the connected stream socket, addr is a pointer to a struct sockaddr (or a struct sockaddr_in) that will hold the information about the other side of the connection, and addrlen is a pointer to an int, that should be initialized to sizeof(struct sockaddr).
The function returns -1 on error and sets errno accordingly.
Once you have their address, you can use inet_ntoa() or gethostbyaddr() to print or get more information. No, you can't get their login name. (Ok, ok. If the other computer is running an ident daemon, this is possible. This, however, is beyond the scope of this document. Check out RFC-1413 for more info.)
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Copyright © 1995, 1996 by Brian "Beej" Hall. This guide may be reprinted in any medium provided that its content is not altered, it is presented in its entirety, and this copyright notice remains intact. Contact firstname.lastname@example.org for more information.