Generation of unique IP-port using bind(0) - c++

Question

I need to generate port numbers for some programm. Google tells, that bind with zero-port generates binds unused port. I want to bind zero-port, remember it's number, close port. Trying to do this? but netstat doesn't see my programm's port. Linux 2.6.27
int sfd;
struct sockaddr_in my_addr;
sfd = socket(PF_INET , SOCK_STREAM, 0);
if (sfd == -1)
{
printf("socket error\n");
return -1;
}
memset(&my_addr, 0, sizeof(struct sockaddr_in ));
my_addr.sin_family = AF_INET;
my_addr.sin_addr.s_addr = INADDR_ANY;
my_addr.sin_port = 0;
if (bind(sfd, (struct sockaddr_in *) &my_addr,
sizeof(struct sockaddr_in)) == -1)
printf("bind error\n");
if (listen(sfd, LISTEN_BACKLOG) == -1)
printf("listen error\n");

Answer 1

bind() expects a sockaddr* not a sockaddr_in*:
bind(sfd, (struct sockaddr *) &my_addr, sizeof(my_addr))
Other than that, I don't see any other errors. Binding to port 0 is the correct way to bind to a random available port. If bind() and listen() do not report a failure then netstat should see an open port. Use getsockname() to find out which port bind() actually chose, eg:
int sfd = socket(PF_INET , SOCK_STREAM, 0);
if (sfd == -1)
{
printf("socket error: %d\n", errno);
return -1;
}
struct sockaddr_in my_addr;
memset(&my_addr, 0, sizeof(my_addr));
my_addr.sin_family = AF_INET;
my_addr.sin_addr.s_addr = INADDR_ANY;
my_addr.sin_port = 0;
if (bind(sfd, (struct sockaddr *) &my_addr, sizeof(my_addr)) == -1)
{
printf("bind error: %d\n", errno);
close(sfd);
return -1;
}
if (listen(sfd, LISTEN_BACKLOG) == -1)
{
printf("listen error: %d\n", errno);
close(sfd);
return -1;
}
memset(&my_addr, 0, sizeof(my_addr));
socklen_t my_addrlen = sizeof(my_addr);
if (getsockname(sfd, (struct sockaddr *) &my_addr, &my_addrlen ) == -1)
{
printf("getsockname error: %d\n", errno);
close(sfd);
return -1;
}
printf("listening on port: %hu\n", ntohs(my_addr.sin_port));