Socket Address Data Structures

The sockaddr data structure is used to provide a generic name for a socket. The following figure illustrates this data structure:
sockaddr Structure

The <SYS\SOCKET.H> file contains this data structure. The sa_len field specifies how long the address is; this field is only used with routing sockets. The family (sa_family) identifies which protocol family this address corresponds to. The contents of the socket address data (sa_data) field depend on the protocol in use.

Additional data structures are defined that correspond to a particular protocol family and overlay the sockaddr structure. The types of socket address data structures are as follows:

Socket Address Data Structures

┌────────────────────────────────────────────────────────────────────┐
│Data Structure        sa_family Value  Protocol     Header File     │
├────────────────────────────────────────────────────────────────────┤
│struct sockaddr_in    AF_INET          TCP/IP       <NETINET\IN.H>  │
├────────────────────────────────────────────────────────────────────┤
│struct sockaddr_un    AF_OS2 or        Local IPC    <SYS\UN.H>      │
│                      AF_UNIX                                       │
├────────────────────────────────────────────────────────────────────┤
│struct sockaddr_nb    AF_NETBIOS or    NetBIOS      <NETNB\NB.H>    │
│                      AF_NB                                         │
└────────────────────────────────────────────────────────────────────┘

The contents of the various socket addresses are as follows:

Internet

A socket name in the internet domain is an internet address, made up of a 32-bit IP address and a 16-bit port number. The 32-bit address is composed of network and host parts; the network part is variable in size. The host part can be interpreted optionally as a subnet field plus the host on a subnet; this is enabled by setting a network address mask.

A socket name in the OS/2 or UNIX domain is a unique listing of ASCII characters of up to 108 bytes.

A socket name in the NetBIOS domain is made up of a 16-byte NetBIOS name and is used as is.