Error codes.

The error code argument unifies with the error code returned by the corresponding socket commands. The error code -2 signifies timeout for timeout-enabled primitives (see below). The error code of zero signifies normal termination. Positive error codes denote specific failures, as defined in BSD sockets. When such a failure occurs, an error message is printed, but the predicate succeeds anyway. The specific error codes are part of the socket documentation. Unfortunately, the symbolic names and error numbers of these failures are different between Unix compilers and Visual C++. Thus, there is no portable, reliable way to refer to these error codes. The only reliably portable error codes that can be used in XSB programs defined through these symbolic constants:

#include "socket_defs_xsb.h"  

#define SOCK_OK       0      /* indicates sucessful return from socket      */
#define SOCK_EOF     -1      /* end of file in socket_recv, socket_get0     */

#include "timer_defs_xsb.h"

#define TIMEOUT_ERR -2                 /* Timeout error code */