php developer blog

Catching Warnings and Notices

by Dominik Jungowski

15. November 2008 comments feed

Simple example: You want to open a file in PHP and there might be a slight possibility, that the file doesn't exist. Your code probably looks like this:

$fileHandle = fopen('text.txt', 'r');
if (!$fileHandle) {
	print("Couldn't open file");
}

According to the php documentation, fopen will return FALSE if it can't open the file, but (and that's the annoying part), it will also generate a warning. Furthermore the php documentation suggests using @ before the function call to suppress the warning. Using @ before a function call is really, really bad coding and it makes your code slow (since @ changes the error_reporting to E_NONE before the function call and changes it back to what you had before after the function call) . But why return false, when it will generate a warning anyhow? Throwing an Exception would be the better way. Here's a way to do it.

First, we create a class containing a public static method that handles the error:

class ErrorHandler
{
    /**
     * catches php errors / warnings / notices and throws
     * an exception instead
     *
     * @param int $errNo
     * @param string $errStr
    */
    public static function handle($errNo, $errStr=NULL)
    {
        switch ($errNo) {
            case E_WARNING:
                throw new RuntimeException($errStr,$errNo);
            break;
            default:
                throw new Exception($errStr,$errNo);
            break;
        }
    }
}

The method handle has the error number and the error message, which are both generated by php. Error number would be something like E_NOTICE, E_WARNING or E_STRICT. The error string in this case would be "failed to open stream: No such file or directory' in /var/www/phpinfo.php:15".

Now we add a public static function method to the same class, that overwrites the php error handler with the method we just wrote:

/**
 * Overwrites the PHP error handler and uses our own
 *
 */
public static function set()
{
	set_error_handler(array(__CLASS__ , 'handle'));
}

Now there's only one thing left to do: We have to call the set method at the beginning of our script:

ErrorHandler::set();

If we now execute the script again, we will not get a warning, instead we'll get an uncaught exception: Fatal error: Uncaught exception 'RuntimeException' with message 'fopen(text.txt) [function.fopen]: failed to open stream: No such file or directory' in /var/www/phpinfo.php:15 Stack trace: #0 [internal function]: ErrorHandler::handle(2, 'fopen(text.txt)…', '/var/www/phpinfo…', 35, Array) #1 /var/www/phpinfo.php(35): fopen('text.txt', 'r') #2 {main} thrown in /var/www/phpinfo.php on line 15

The cool thing is, that now we can simply catch the exception and will not flood the phperror log with Warnings, where they are probably not needed. Our script would now look like this:

ErrorHandler::set();
try {
    $fileHandle = fopen('text.txt', 'r');
} catch(Exception $e) {
    print("Couldn't open file");
}

Note, that you can catch anything but a fatal error.