Scroll to navigation

sockaddr(3type) sockaddr(3type)


sockaddr, sockaddr_storage, sockaddr_in, sockaddr_in6, sockaddr_un, socklen_t, in_addr, in6_addr, in_addr_t, in_port_t, - socket address


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;

Internet domain sockets

#include <netinet/in.h>
struct sockaddr_in {
    sa_family_t     sin_family;     /* AF_INET */
    in_port_t       sin_port;       /* Port number */
    struct in_addr  sin_addr;       /* IPv4 address */
struct sockaddr_in6 {
    sa_family_t     sin6_family;    /* AF_INET6 */
    in_port_t       sin6_port;      /* Port number */
    uint32_t        sin6_flowinfo;  /* IPv6 flow info */
    struct in6_addr sin6_addr;      /* IPv6 address */
    uint32_t        sin6_scope_id;  /* Set of interfaces for a scope */
struct in_addr {
    in_addr_t s_addr;
struct in6_addr {
    uint8_t   s6_addr[16];
typedef uint32_t in_addr_t;
typedef uint16_t in_port_t;

UNIX domain sockets

#include <sys/un.h>
struct sockaddr_un {
    sa_family_t     sun_family;     /* Address family */
    char            sun_path[];     /* Socket pathname */


Describes a socket address.
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.
Describes the length of a socket address. This is an integer type of at least 32 bits.
Describes a socket's protocol family. This is an unsigned integer type.

Internet domain sockets

Describes an IPv4 Internet domain socket address. The sin_port and sin_addr members are stored in network byte order.
Describes an IPv6 Internet domain socket address. The sin6_addr.s6_addr array is used to contain a 128-bit IPv6 address, stored in network byte order.

UNIX domain sockets

Describes a UNIX domain socket address.





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 Issue 8 will fix 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)

2023-04-22 Linux man-pages 6.05.01