sinaddr

Sinaddr, in the context of networking programming, refers to the sin_addr member of the IPv4 socket address structure, struct sockaddr_in. This field stores the IPv4 address associated with a socket endpoint and is used by common socket functions such as bind, connect, and accept. The sin_addr member is of type struct in_addr, which contains a single 32-bit value named s_addr.

In_addr typically represents the IPv4 address in network byte order (big-endian). The s_addr field holds the binary form of the address, and codes often convert it to host byte order for display or arithmetic using functions such as ntohl or inet_ntoa. For textual to binary conversion, programmers traditionally used inet_aton or inet_addr, but inet_pton is the modern, preferred function, paired with inet_ntop for reverse conversion.

Common usage patterns include binding a socket to all local interfaces by setting sin_addr to INADDR_ANY (0.0.0.0), or binding to a specific address by assigning the binary form of the desired IP. Printing or logging the address is typically done with inet_ntoa or inet_ntop, while the associated port is stored in sin_port in network order and converted to host order with ntohs when needed.

Sinaddr is IPv4-specific; for IPv6, a separate field and structure (sin6_addr within struct sockaddr_in6) are used. The canonical name remains sin_addr within sockaddr_in, and the term sinaddr is a shorthand reference found in some documentation or code comments.