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Technical Standard: Networking Services (XNS), Issue 5.2 Draft 2.0
Copyright © 1999 The Open Group
Use of Sockets over Internet Protocols based on IPv4
Support for sockets over Internet Protocols based on IPv4 is mandatory.
This Chapter gives the protocol-specific information that is relevant
to the use of sockets in connection with TCP, UDP and ICMP
over Version 4 of the Internet Protocol - IPv4.
Headers
Symbolic constant
AF_INET
is defined in
<sys/socket.h>
(see
<sys/socket.h>)
to identify the IPv4 Internet address family.
Header
<netinet/in.h>
(see
<netinet/in.h>)
contains other definitions used in connection with IPv4 Internet
sockets.
The
sockaddr_storage
structure defined in
<sys/socket.h>
is large enough to accommodate a
sockaddr_in
structure (see
<netinet/in.h>)
and is aligned at an appropriate boundary so that pointers
to it can be cast as pointers to
sockaddr_in
structures and used to access the fields of those structures without
alignment problems. When a
sockaddr_storage
structure is cast as a
sockaddr_in
structure, the
ss_family
field maps onto the
sin_family
field.