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Allocate a socket descriptor
#include <sys/types.h>
#include <sys/socket.h>
int socket(int domain, int type, int protocol);
Returns a new socket descriptor that you can use to do sockety things with. This is generally the first call in the whopping process of writing a socket program, and you can use the result for subsequent calls to listen(), bind(), accept(), or a variety of other functions.
domain |
domain describes what kind of socket you're interested in. This can, believe me, be a wide variety of things, but since this is a socket guide, it's going to be PF_INET for you. And, correspondingly, when you load up your struct sockaddr_in to use with this socket, you're going to set the sin_family field to AF_INET (Also of interest is PF_INET6 if you're going to be doing IPv6 stuff. If you don't know what that is, don't worry about it...yet.) |
| type | Also, the type parameter can be a number of things, but
you'll probably be setting it to either SOCK_STREAM for
reliable TCP sockets (send(), recv()) or
SOCK_DGRAM for unreliable fast UDP sockets
(sendto(), recvfrom().)
(Another interesting socket type is SOCK_RAW which can be used to construct packets by hand. It's pretty cool.) |
| protocol | Finally, the protocol parameter tells which protocol to use with a certain socket type. Like I've already said, for instance, SOCK_STREAM uses TCP. Fortunately for you, when using SOCK_STREAM or SOCK_DGRAM, you can just set the protocol to 0, and it'll use the proper protocol automatically. Otherwise, you can use getprotobyname() to look up the proper protocol number. |
The new socket descriptor to be used in subsequent calls, or -1 on error (and errno will be set accordingly.)
int s1, s2;
s1 = socket(PF_INET, SOCK_STREAM, 0);
s2 = socket(PF_INET, SOCK_DGRAM, 0);
if (s1 == -1) {
perror("socket");
}
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