I have used XAMPP for Home windows.

\xampp\apache\logs\error.log, where xampp is the installation folder. Should you haven't transformed the error_log establishing PHP (seek advice from phpinfo()), it will likely be drenched towards the Apache log.

Try looking in your configuration file and check for that error_log setting. Or use phpinfo() to locate this setting.

This can be an easy situation from the PHP error log being turned off.