int syslog(int priority, string message);
syslog() generates a log message that will be distributed by the system logger. priority is a combination of the facility and the level, values for which are given in the next section. The remaining argument is the message to send, except that the two characters %m will be replaced by the error message string (strerror) corresponding to the present value of errno.
More information on the syslog facilities can be found in the man pages for syslog on Unix machines.
On Windows NT, the syslog service is emulated using the Event Log.