Using PF_LOCAL and SOCK_STREAM

You will use a zero for the protocol argument in the socket(2) or socketpair(2) functions for PF_LOCAL sockets. This is the only supported value for that argument. A valid socket(2) call using PF_LOCAL and SOCK_STREAM is shown as follows:

Example

int s;

s = socket(PF_LOCAL,SOCK_STREAM,0);

if ( s == -1 )

{

   perror("socket()");

}

This creates a stream socket to allow one process to communicate with another process within the same host. The steps are

1. Integer s is declared to receive the socket number (it is treated the same as a file descriptor).
2. The socket(2) function is called. The domain argument is set to PF_LOCAL, and the socket type argument is set to SOCK_STREAM to request a stream socket. The protocol argument is set to zero, which is the only valid value for PF_LOCAL sockets.
3. The value s is tested to see whether it is the value -1. If it is, then an error has occurred, and errno has the reason for it. Function perror(3) is used in this example to report what the errno code indicates.
4. If s is not -1, then it represents a valid socket. It can be used in most places in which a file descriptor is valid (in read(2) and write(2) function calls, for example).

See an example using AF_LOCAL (same as PF_LOCAL)SOCK_STREAM

NOTE

At the present time, zero is the only valid value for the protocol argument of the socket(2) or socketpair(2) function calls, when the domain argument is PF_LOCAL (or PF_UNIX).