bindresvport() - bind a socket to a privileged IP port
#include <sys/types.h>
#include <netinet/in.h>
int bindresvport(int sd, struct socaddr_in *sin)
bindresvport(3) is used to bind a socket descriptor to a privileged IP port, that is, a port number in the range 0-1023. The routine returns 0 if it is successful, otherwise -1 is returned and errno set to reflect the cause of the error.
Only a privileged user can bind to a privileged port; this call will fail for any other users.