socket

int sockfd, n;

if (sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0)
    err_sys("socket error");

The socket function creates an Internet (AF_INET) stream (SOCK_STREAM) socket, which is a fancy name for a TCP socket. The function returns a small integer descriptor that we can use to identify the socket in all future function calls (e.g., the calls to connect and read that follow).