Manual Pages  — INET

struct sockaddr_in {
        uint8_t         sin_len;
        sa_family_t     sin_family;
        in_port_t       sin_port;
        struct in_addr  sin_addr;
        char            sin_zero[8];
};

Sockets may be created with the local address INADDR_ANY to affect "wildcard" matching on incoming messages. The address in a connect(2) or sendto(2) call may be given as INADDR_ANY to mean "this host". The distinguished address INADDR_BROADCAST is allowed as a shorthand for the broadcast address on the primary network if the first network configured supports broadcast.

The inet address on an interface consist of the address itself, the netmask, either broadcast address in case of a broadcast interface or peers address in case of point-to-point interface. The following ioctl(2) commands are provided for a datagram socket in the Internet domain:

SIOCAIFADDR	Add address to an interface. The command requires struct in_aliasreq as argument.
SIOCDIFADDR	Delete address from an interface. The command requires struct ifreq as argument.
SIOCGIFADDR SIOCGIFBRDADDR SIOCGIFDSTADDR SIOCGIFNETMASK
	Return address information from interface. The returned value is in struct ifreq. This way of address information retrieval is obsoleted, a preferred way is to use getifaddrs(3) API.

PS1, 7, An Introductory 4.3 BSD Interprocess Communication Tutorial,

PS1, 8, An Advanced 4.3 BSD Interprocess Communication Tutorial,