How to log error message in drupal

Question

How to log our own error messages(for ex: error due to invalid user date entry) which is generated in php program to drupal error log.

Answer 1

You can use the watchdog function :

watchdog($type, $message, $variables = array(), $severity = WATCHDOG_NOTICE, $link = NULL)

Quoting the manual, the parameters are :

• $type The category to which this message belongs.
• $message The message to store in the log.
• $variables Array of variables to replace in the message on display or NULL if message is already translated or not possible to translate.
• $severity The severity of the message, as per RFC 3164
• $link A link to associate with the message.

And the error levels can be found on the page of watchdog_severity_levels. For an error, you'll most probably use WATCHDOG_ERROR, or maybe even something more "critical", depending on the kind of error.