addrlen

addrlen is a conventional variable name used in socket programming to denote the length of a socket address structure, typically a value used with operations involving storing or providing a socket address. In many APIs, the address is stored in a struct such as sockaddr, sockaddr_in, or sockaddr_in6, and addrlen specifies the size of that structure.

In POSIX systems, the length is typically of type socklen_t. In Windows Sockets, the corresponding parameter is an int. The addrlen parameter is usually used as an in/out value. For example, in accept, you provide the address buffer and its length; on return, addrlen contains the actual length of the peer address. In getsockname and getpeername, you pass a pointer to addrlen to receive the length of the returned address. In sendto and recvfrom, you pass the length of the destination or source address.

Best practices include initializing addrlen to the size of the buffer you pass (e.g., sizeof(struct sockaddr_storage)) and checking that the function succeeds, then using the returned length to interpret the address. If the buffer is too small, the call fails and may set errno (or a Windows error).

Using portable types like sockaddr_storage for temporary buffers, and socklen_t for the length when possible, helps maintain cross-platform compatibility.

See also socklen_t, sockaddr, getsockname, getpeername, accept, sendto, recvfrom.