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Connect a socket to a server
#include <sys/types.h>
#include <sys/socket.h>
int connect(int sockfd, const struct sockaddr *serv_addr,
socklen_t addrlen);
Once you've built a socket descriptor with the socket() call, you can connect() that socket to a remote server using the well-named connect() system call. All you need to do is pass it the socket descriptor and the address of the server you're interested in getting to know better. (Oh, and the length of the address, which is commonly passed to functions like this.)
If you haven't yet called bind() on the socket descriptor, it is automatically bound to your IP address and a random local port. This is usually just fine with you, since you really don't care what your local port is; you only care what the remote port is so you can put it in the serv_addr parameter. You can call bind() if you really want your client socket to be on a specific IP address and port, but this is pretty rare.
Once the socket is connect()ed, you're free to send() and recv() data on it to your heart's content.
Special note: if you connect() a SOCK_DGRAM UDP socket to a remote host, you can use send() and recv() as well as sendto() and recvfrom(). If you want.
Returns zero on success, or -1 on error (and errno will be set accordingly.)
int s;
struct sockaddr_in serv_addr;
// pretend the server is at 63.161.169.137 listening on port 80:
myaddr.sin_family = AF_INET;
myaddr.sin_port = htons(80);
inet_aton("63.161.169.137", &myaddr.sin_addr.s_addr);
s = socket(PF_INET, SOCK_STREAM, 0);
connect(s, (struct sockaddr*)myaddr, sizeof(myaddr));
// now we're ready to send() and recv()
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