SOCKADDR

sockaddr is a generic socket address structure used in the Berkeley sockets API. It provides a common header for address data across different address families. In C, it is defined as a struct with at least two members: sa_family, of type sa_family_t, which indicates the address family (such as AF_INET, AF_INET6, or AF_UNIX); and sa_data, a character array that holds the rest of the address information. The exact contents and size of sa_data vary by family.

Because the concrete address formats differ, actual addresses are stored in family-specific structures such as sockaddr_in for IPv4, sockaddr_in6 for IPv6, and sockaddr_un for UNIX domain sockets. These family-specific structures begin with the same sa_family field, which allows code to determine the family after casting the pointer to sockaddr*.

Usage in networking code commonly involves passing a pointer to a sockaddr and a socklen_t length to socket API functions such as bind, connect, accept, sendto, recvfrom, getsockname, and getpeername. When you work with a specific address family, you usually fill in the appropriate fields (for IPv4: sin_family, sin_port, sin_addr) and then cast the pointer to struct sockaddr* for the API call. To hold any address type, programs may use struct sockaddr_storage, a large enough buffer to accommodate the largest sockaddr type.

Common header files include <sys/socket.h> and, depending on the family, <netinet/in.h>, <arpa/inet.h>, or <sys/un.h>. See also sockaddr_in, sockaddr_in6, sockaddr_un, sockaddr_storage, and the AF_* constants.