sockaddr

The sockaddr structure varies depending on the protocol selected. Except for the sin*_family parameter, sockaddr contents are expressed in network byte order.

Winsock functions using sockaddr are not strictly interpreted to be pointers to a sockaddr structure. The structure is interpreted differently in the context of different address families. The only requirements are that the first u_short is the address family and the total size of the memory buffer in bytes is namelen.

The SOCKADDR_STORAGE structure also stores socket address information and the structure is sufficiently large to store IPv4 or IPv6 address information. The use of the SOCKADDR_STORAGE structure promotes protocol-family and protocol-version independence, and simplifies development. It is recommended that the SOCKADDR_STORAGE structure be used in place of the sockaddr structure. The SOCKADDR_STORAGE structure is supported on Windows Server 2003 and later.

The sockaddr structure and sockaddr_in structures below are used with IPv4. Other protocols use similar structures.

struct sockaddr {
        ushort  sa_family;
        char    sa_data[14];
};

struct sockaddr_in {
        short   sin_family;
        u_short sin_port;
        struct  in_addr sin_addr;
        char    sin_zero[8];
};

The sockaddr_in6 and sockaddr_in6_old structures below are used with IPv6.

struct sockaddr_in6 {
        short   sin6_family;
        u_short sin6_port;
        u_long  sin6_flowinfo;
        struct  in6_addr sin6_addr;
        u_long  sin6_scope_id;
};

typedef struct sockaddr_in6 SOCKADDR_IN6;
typedef struct sockaddr_in6 *PSOCKADDR_IN6;
typedef struct sockaddr_in6 FAR *LPSOCKADDR_IN6;


struct sockaddr_in6_old {
        short   sin6_family;        
        u_short sin6_port;          
        u_long  sin6_flowinfo;      
        struct  in6_addr sin6_addr;  
};

On the Microsoft Windows Software Development Kit (SDK) released for Windows Vista and later, SOCKADDR and SOCKADDR_IN typedef tags are defined for sockaddr and sockaddr_in structures as follows:

typedef struct sockaddr {
#if (_WIN32_WINNT < 0x0600)
    u_short sa_family;
#else 
    ADDRESS_FAMILY sa_family;
#endif //(_WIN32_WINNT < 0x0600)
    CHAR sa_data[14];
} SOCKADDR, *PSOCKADDR, FAR *LPSOCKADDR;


typedef struct sockaddr_in {
#if(_WIN32_WINNT < 0x0600)
    short   sin_family;    
#else //(_WIN32_WINNT < 0x0600)
    ADDRESS_FAMILY sin_family;
#endif //(_WIN32_WINNT < 0x0600)
    USHORT sin_port;
    IN_ADDR sin_addr;
    CHAR sin_zero[8];
} SOCKADDR_IN, *PSOCKADDR_IN;

On the Windows SDK released for Windows Vista and later, the organization of header files has changed and the sockaddr and sockaddr_in structures are defined in the Ws2def.h header file, not the Winsock2.h header file. The Ws2def.h header file is automatically included by the Winsock2.h header file. The sockaddr_in6 structure is defined in the Ws2ipdef.h header file, not the Ws2tcpip.h header file. The Ws2ipdef.h header file is automatically included by the Ws2tcpip.h header file. The Ws2def.h and Ws2ipdef.h header files should never be used directly.

Example Code

The following example demonstrates the use of the sockaddr structure.

// Declare variables
SOCKET ListenSocket;
struct sockaddr_in saServer;
hostent* localHost;
char* localIP;

// Create a listening socket
ListenSocket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);

// Get the local host information
localHost = gethostbyname("");
localIP = inet_ntoa (*(struct in_addr *)*localHost->h_addr_list);

// Set up the sockaddr structure
saServer.sin_family = AF_INET;
saServer.sin_addr.s_addr = inet_addr(localIP);
saServer.sin_port = htons(5150);

// Bind the listening socket using the
// information in the sockaddr structure
bind( ListenSocket,(SOCKADDR*) &saServer, sizeof(saServer) );

See Also

SOCKADDR_STORAGE