.\" Copyright 2020, Michael Kerrisk <mtk.manpages@gmail.com>
.\" Copyright, the authors of the Linux man-pages project
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.TH sockaddr 3type 2026-02-08 "Linux man-pages 6.19"
.SH NAME
sockaddr, sockaddr_storage, socklen_t
\- socket address
.SH LIBRARY
Standard C library
.RI ( libc )
.SH SYNOPSIS
.EX
.B #include <sys/socket.h>
.P
.B struct sockaddr {
.BR "    sa_family_t     sa_family;" "      /* Address family */"
.BR "    char            sa_data[];" "      /* Socket address */"
.B };
.P
.B struct sockaddr_storage {
.BR "    sa_family_t     ss_family;" "      /* Address family */"
.B };
.P
.BR typedef " /* ... */ " socklen_t;
.BR typedef " /* ... */ " sa_family_t;
.P
.EE
.SH DESCRIPTION
.TP
.I sockaddr
Describes a socket address.
.TP
.I sockaddr_storage
A structure at least as large as any other
.IR sockaddr_ *
address structures.
It's aligned so that a pointer to it can be cast
as a pointer to other
.IR sockaddr_ *
structures and used to access its fields.
.TP
.I socklen_t
Describes the length of a socket address.
This is an integer type of at least 32 bits.
.TP
.I sa_family_t
Describes a socket's protocol family.
This is an unsigned integer type.
.SS Internet domain sockets
See
.BR sockaddr_in (3type)
and
.BR sockaddr_in6 (3type).
.SS UNIX domain sockets
See
.BR sockaddr_un (3type).
.SH STANDARDS
POSIX.1-2024.
.SH HISTORY
POSIX.1-2001.
.P
.I socklen_t
was invented by POSIX.
See also
.BR accept (2).
.P
These structures were invented before modern ISO C strict-aliasing rules.
If aliasing rules are applied strictly,
these structures would be extremely difficult to use
without invoking undefined behavior.
POSIX.1-2024 fixed this
by requiring that implementations
make sure that these structures
can be safely used as they were designed.
.SH NOTES
.I socklen_t
is also defined in
.IR <netdb.h> .
.P
.I sa_family_t
is also defined in
.I <netinet/in.h>
and
.IR <sys/un.h> .
.SH SEE ALSO
.BR accept (2),
.BR bind (2),
.BR connect (2),
.BR getpeername (2),
.BR getsockname (2),
.BR getsockopt (2),
.BR sendto (2),
.BR setsockopt (2),
.BR socket (2),
.BR socketpair (2),
.BR getaddrinfo (3),
.BR gethostbyaddr (3),
.BR getnameinfo (3),
.BR htonl (3),
.BR ipv6 (7),
.BR socket (7)