Microsoft Developer Network

SOCKADDR and SOCKADDR_IN

The SOCKADDR structure is a generic address structure used by Winsock. The SOCKADDR_IN structure is a specific implementation for Internet Protocol version 4 (IPv4) addresses.

struct sockaddr {
    u_short sa_family;       // Address family
    char    sa_data[14];     // Up to 14 bytes of the socket address
};

struct sockaddr_in {
    short int           sin_family;   // Address family (AF_INET)
    unsigned short int  sin_port;     // Port number
    struct in_addr      sin_addr;     // Internet address
    char                sin_zero[8];  // Not used
};
                    

sa_family: Specifies the address family. For IPv4, this is AF_INET.

sin_port: The port number, in network byte order.

sin_addr: An in_addr structure containing the IPv4 address.

IN_ADDR

The IN_ADDR structure represents an IPv4 address.

struct in_addr {
    union {
        struct {
            u_char s_b1, s_b2, s_b3, s_b4;
        } S_un_b;
        struct {
            u_short s_w1, s_w2;
        } S_un_w;
        u_long S_addr;
    } S_un;
};
                    

S_addr: Stores the IPv4 address as a 32-bit unsigned integer, in network byte order.

WSAPOLLFD

The WSAPOLLFD structure is used with the WSAPoll function to specify a set of file descriptors to monitor for readiness.

typedef struct wsapollfd {
    SOCKET   fd;
    short    events;
    short    revents;
} WSAPOLLFD, *PWSAPOLLFD;
                    

fd: The socket descriptor.

events: The events to monitor (e.g., POLLIN, POLLOUT).

revents: The events that have occurred.

TIMEVAL

The TIMEVAL structure is used for specifying time-out values for blocking socket operations.

struct timeval {
    long tv_sec;  // Seconds
    long tv_usec; // Microseconds
};
                    

tv_sec: The number of seconds.

tv_usec: The number of microseconds.

FD_SET

The FD_SET structure (or rather, a macro that manages an array of SOCKET descriptors) is used with select() to specify a set of sockets to monitor for read, write, or exceptional conditions.

Note: While conceptually a structure, FD_SET is typically implemented as an opaque type and manipulated via macros.

Key macros:

• FD_ZERO(fdset): Clears all socket descriptors from the set.
• FD_SET(s, fdset): Adds a socket descriptor to the set.
• FD_CLR(s, fdset): Removes a socket descriptor from the set.
• FD_ISSET(s, fdset): Checks if a socket descriptor is in the set.