#include <sys/types.h> #include <netinet/in.h> int bindresvport(int sockfd, struct sockaddr_in *sin);
bindresvport() is used to bind a socket descriptor to a privileged anonymous IP port, that is, a port number arbitrarily selected from the range 512 to 1023.
If the bind(2) performed by bindresvport() is successful, and sin is not NULL, then sin->sin_port returns the port number actually allocated.
sin can be NULL, in which case sin->sin_family is implicitly taken to be AF_INET. However, in this case, bindresvport() has no way to return the port number actually allocated. (This information can later be obtained using getsockname(2).)
glibc >= 2.17: MT-Safe
glibc < 2.17: MT-Unsafe