Programming PHP

time the error happened. Your error handler should check the current level of errors
being reported with error_reporting( ) and act appropriately.
The call to set_error_handler( ) returns the current error handler. You can restore
the previous error handler either by calling set_error_handler( ) with the returned
value when your script is done with its own error handler, or by calling the restore_
error_handler( ) function.
The following code shows how to use an error handler to format and print errors:
function display_error($error, $error_string, $filename, $line, $symbols) {
echo "The error '$error_string' occurred in the file '$filename'
on line $line.";
}
set_error_handler('display_error');
$value = 4 / 0; // divide by zero error
The error 'Division by zero' occurred in the file
'err-2.php' on line 8.
Logging in error handlers
PHP provides a built-in function, error_log( ), to log errors to the myriad places
where administrators like to put error logs:
error_log(message, type [, destination [, extra_headers ]]);
The first parameter is the error message. The second parameter specifies where the
error is logged: a value of 0 logs the error via PHP’s standard error-logging mechanism;
a value of 1 emails the error to the destination address, optionally adding any
extra_headers to the message; a value of 3 appends the error to the destination file.
To save an error using PHP’s logging mechanism, call error_log( ) with a type of 0.By
changing the value of error_log in your php.ini file, you can change which file to log
into. If you set error_log to syslog, the system logger is used instead. For example:
error_log('A connection to the database could not be opened.', 0);
To send an error via email, call error_log( ) with a type of 1. The third parameter is
the email address to which to send the error message, and an optional fourth parameter
can be used to specify additional email headers. Here’s how to send an error
message by email:
error_log('A connection to the database could not be opened.', 1, 'errors@php.net');
Finally, to log to a file, call error_log( ) with a type of 3. The third parameter specifies
the name of the file to log into:
error_log('A connection to the database could not be opened.', 3, '/var/log/php_
errors.log');
Example 13-5 shows an example of an error handler that writes logs into a file and
rotates the log file when it gets above 1 KB.
306 | Chapter 13: Application Techniques
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