6-16 slenの変化を知る
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
int
main()
{
  int sock;
  struct sockaddr_storage addr;
  socklen_t slen;
  sock = socket(AF_INET, SOCK_DGRAM, 0);
  slen = sizeof(addr);
  printf("%d\n", slen);
  getsockname(sock, (struct sockaddr *)&addr, &slen);
  printf("%d\n", slen);
  return 0;
}
