sockaddr, sockaddr_storage, socklen_t

Standard C library (libc)

#include <sys/socket.h>

struct sockaddr {
    sa_family_t     sa_family;      /* Address family */
    char            sa_data[];      /* Socket address */
};

struct sockaddr_storage {
    sa_family_t     ss_family;      /* Address family */
};

typedef /* ... */ socklen_t;
typedef /* ... */ sa_family_t;

sockaddr

Describes a socket address.

sockaddr_storage

A structure at least as large as any other sockaddr_* address structures. It's aligned so that a pointer to it can be cast as a pointer to other sockaddr_* structures and used to access its fields.

socklen_t

Describes the length of a socket address. This is an integer type of at least 32 bits.

sa_family_t

Describes a socket's protocol family. This is an unsigned integer type.

POSIX.1-2024.

POSIX.1-2001.

socklen_t was invented by POSIX. See also accept(2).

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.

socklen_t is also defined in <netdb.h>.

sa_family_t is also defined in <netinet/in.h> and <sys/un.h>.

accept(2), bind(2), connect(2), getpeername(2), getsockname(2), getsockopt(2), sendto(2), setsockopt(2), socket(2), socketpair(2), getaddrinfo(3), gethostbyaddr(3), getnameinfo(3), htonl(3), ipv6(7), socket(7)