- What port am I on?
- Once you have a socket, you might have to associate that socket with a port on your local machine. (This is commonly done if you’re going to listen() for incoming connections on a specific port—multiplayer network games do this when they tell you to “connect to 192.168.5.10 port 3490”.) The port number is used by the kernel to match an incoming packet to a certain process’s socket descriptor.
#include <sys/types.h>
#include <sys/socket.h>
int bind(int sockfd, struct sockaddr *my_addr, int addrlen);
Parameters
sockfd is the socket file descriptor returned by socket()my_addr is a pointer to a struct sockaddr that contains information about your address, namely, port and IP address.
(struct sockaddr *) &sockaddr
addrlen is the length in bytes of that address.
return values
bind() also returns -1 on error and sets errno to the error’s value.
example
struct addrinfo hints, *res;
int sockfd;
// first, load up address structs with getaddrinfo():
memset(&hints, 0, sizeof hints);
hints.ai_family = AF_UNSPEC; // use IPv4 or IPv6, whichever
hints.ai_socktype = SOCK_STREAM;
hints.ai_flags = AI_PASSIVE; // fill in my IP for me
getaddrinfo(NULL, "3490", &hints, &res);
// make a socket:
sockfd = socket(res->ai_family, res->ai_socktype, res->ai_protocol);
// bind it to the port we passed in to getaddrinfo():
bind(sockfd, res->ai_addr, res->ai_addrlen);