getsockname man page
getsockname — get socket name
#include <sys/socket.h> int getsockname(int sockfd, struct sockaddr *addr, socklen_t *addrlen);
getsockname() returns the current address to which the socket sockfd is bound, in the buffer pointed to by addr. The addrlen argument should be initialized to indicate the amount of space (in bytes) pointed to by addr. On return it contains the actual size of the socket address.
The returned address is truncated if the buffer provided is too small; in this case, addrlen will return a value greater than was supplied to the call.
On success, zero is returned. On error, -1 is returned, and errno is set appropriately.
The argument sockfd is not a valid file descriptor.
The addr argument points to memory not in a valid part of the process address space.
addrlen is invalid (e.g., is negative).
Insufficient resources were available in the system to perform the operation.
The file descriptor sockfd does not refer to a socket.
POSIX.1-2001, POSIX.1-2008, SVr4, 4.4BSD (getsockname() first appeared in 4.2BSD).
For background on the socklen_t type, see accept(2).
bind(2), socket(2), getifaddrs(3), ip(7), socket(7), unix(7)
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bind(2), bindresvport(3), connect(2), explain(1), explain(3), explain_getsockname(3), explain_getsockname_or_die(3), getifaddrs(3), getnameinfo(3), getpeereid.3bsd(3), getpeername(2), if_nameindex(3), signal-safety(7), socket(2), socket(7), socketcall(2), syscalls(2), unix(7).