On Apache, vhosts can be configured with their own error log file, like so:
How would this be done when hosting PHP under IIS?
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To report errors in the Event viewer, go to your php.ini and make sure logging is on.
log_errors = On
then enable error_log to write to syslog (with is the Event Viewer on Windows machines)
error_log = syslog
If using 'shared' hosting windows hosting then you most likely have a control panel that should have some kind of logging, otherwise see method above.