Web Database Applications with PHP and MySQL, 2nd Edition

Throwing and Catching Exceptions

PHP 5 has introduced an exception model that allows objects to be thrown and caught using the throw and try...catch statements.

The throw and try...catch statements provide a way of jumping to error handling code in exceptional circumstances: rather than terminating a script with a fatal error, exceptions are thrown, and can be caught and processed. The throw statement is always used in conjunction with the try...catch statement, and the following fragment shows the basic structure:

$total = 100;
$n = 5;

$result;

try
{
    // Check the value of $n before we use it
    if ($n == 0)
        throw new Exception("Can't set n to zero.");

    // Calculate an average
    $result = $total / $n;
}
catch (Exception $x)
{
    print "There was an error: {$x->getMessage( )};
}

The block of statements contained in the braces that follow the try keyword are executed normally as part of the script; the braces are required, even for a single statement. If a throw statement is called in the try block, then the statements contained in the braces that follow the catch keyword are executed. The throw statement throws an object and the catch block of code catches the thrown object, assigning it to the variable specified.

The catch statement specifies the type of object that is caught by placing the class name before the variable: the following fragment catches Exception objects and assigns them to the variable $x:

catch (Exception $x)
{
    print "There was an error: {$x->getMessage( )};
}

Specifying ...