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GETSOCKNAME(2)              BSD System Calls Manual             GETSOCKNAME(2)

     getsockname -- get socket name

     #include <&lt;sys/socket.h>&gt;

     getsockname(int s, struct sockaddr *name, socklen_t *namelen);

     getsockname() returns the locally bound address information for a speci-
     fied socket.

     Common uses of this function are as follows:

     o   When bind(2) is called with a port number of 0 (indicating the kernel
         should pick an ephemeral port) getsockname() is used to retrieve the
         kernel-assigned port number.

     o   When a process calls bind(2) on a wildcard IP address, getsockname()
         is used to retrieve the local IP address for the connection.

     o   When a function wishes to know the address family of a socket,
         getsockname() can be used.

     getsockname() takes three parameters:

     s contains the file descriptor for the socket to be looked up.

     name points to a sockaddr structure which will hold the resulting address
     information.  Normal use requires one to use a structure specific to the
     protocol family in use, such as sockaddr_in (IPv4) or sockaddr_in6
     (IPv6), cast to a (struct sockaddr *).

     For greater portability (such as newer protocol families) the new struc-
     ture sockaddr_storage exists.  sockaddr_storage is large enough to hold
     any of the other sockaddr_* variants.  On return, it should be cast to
     the correct sockaddr type, according to the current protocol family.

     namelen indicates the amount of space pointed to by name, in bytes.  Upon
     return, namelen is set to the actual size of the returned address infor-

     If the address of the destination socket for a given socket connection is
     needed, the getpeername(2) function should be used instead.

     If name does not point to enough space to hold the entire socket address,
     the result will be truncated to namelen bytes.

     On success, getsockname() returns a 0, and namelen is set to the actual
     size of the socket address returned in name.  Otherwise, errno is set,
     and a value of -1 is returned.

     If getsockname() fails, errno is set to one of the following:

     [EBADF]            The argument s is not a valid descriptor.

     [ENOTSOCK]         The argument s is a file, not a socket.

     [ENOBUFS]          Insufficient resources were available in the system to
                        perform the operation.

     [EFAULT]           The name or namelen parameter points to memory not in
                        a valid part of the process address space.

     accept(2), bind(2), getpeername(2), socket(2), getpeereid(3)

     The getsockname() function conforms to IEEE Std 1003.1-2008

     The getsockname() function call appeared in 4.2BSD.

BSD                             March 28, 2017                             BSD