Exception Handling and Error Reporting

Exception and Error handling

try/catch

try..catch blocks can be used to control the flow of a program where Exceptions may be thrown. They can be caught and handled gracefully rather than letting PHP stop when one is encountered:

try {
    // Do a bunch of things...
    throw new Exception('My test exception!');
} catch (Exception $ex) {
    // Your logic failed. What do you want to do about that? Log it:
    file_put_contents('my_error_log.txt', $ex->getMessage(), FILE_APPEND);
}

The above example would catch the Exception thrown in the try block and log it's message ("My test exception!") to a text file.

Catching different Exception types

You can implement multiple catch statements for different types of exceptions to be handled in different ways, for example:

try {
    throw new InvalidArgumentException('Argument #1 must be an integer!');
} catch (InvalidArgumentException $ex) {
    var_dump('Invalid argument exception caught: ' . $ex->getMessage());
} catch (Exception $ex) {
    var_dump('Standard exception caught: ' . $ex->getMessage());
}

In the above example the first catch will be used since it matches first in the order of execution. If you swapped the order of the catch statements around, the Exception catcher would execute first.

Similarly, if you were to throw an UnexpectedValueException instead you would see the second handler for a standard Exception being used.

finally

If you need something to be done after either a try or a catch has finished running, you can use a finally statement:

try {
    throw new Exception('Hello world');
} catch (Exception $e) {
    echo 'Uh oh! ' . $e->getMessage();
} finally {
    echo " - I'm finished now - home time!";
}

The above example would output the following:

Uh oh! Hello world - I'm finished now - home time!

throwable

In PHP 7 we see the introduction of the Throwable interface, which Error as well as Exception implements. This adds a service contract level between exceptions in PHP 7, and allows you to implement the interface for your own custom exceptions:

$handler = function(\Throwable $ex) {
    $msg = "[ {$ex->getCode()} ] {$ex->getTraceAsString()}";
    mail('admin@server.com', $ex->getMessage(), $msg);
    echo myNiceErrorMessageFunction();
};
set_exception_handler($handler);
set_error_handler($handler);

Prior to PHP 7 you can simply typehint Exception since as of PHP 5 all exception classes extend it.

Logging fatal errors

In PHP, a fatal error is a kind of error that cannot be caught, that is, after experiencing a fatal error a program does not resume. However, to log this error or somehow handle the crash you can use register_shutdown_function to register shutdown handler.

function fatalErrorHandler() {
    // Let's get last error that was fatal.
    $error = error_get_last();
   
    // This is error-only handler for example purposes; no error means that
    // there were no error and shutdown was proper. Also ensure it will handle 
    // only fatal errors.
    if (null === $error || E_ERROR != $error['type']) {
        return;
    }

    // Log last error to a log file.
    // let's naively assume that logs are in the folder inside the app folder.
    $logFile = fopen("./app/logs/error.log", "a+");

    // Get useful info out of error.
    $type    = $error["type"];
    $file    = $error["file"];
    $line    = $error["line"];
    $message = $error["message"]

    fprintf(
        $logFile,
        "[%s] %s: %s in %s:%d\n",
        date("Y-m-d H:i:s"),
        $type,        
        $message,
        $file, 
        $line);

    fclose($logFile);       
}


register_shutdown_function('fatalErrorHandler');

Reference:

Setting error reporting and where to display them

If it's not already done in php.ini, error reporting can be set dynamically and should be set to allow most errors to be shown:

Syntax

int error_reporting ([ int $level ] )

Examples

// should always be used prior to 5.4
error_reporting(E_ALL);

// -1 will show every possible error, even when new levels and constants are added 
// in future PHP versions. E_ALL does the same up to 5.4.
error_reporting(-1);

// without notices
error_reporting(E_ALL & ~E_NOTICE);

// only warnings and notices.
// for the sake of example, one shouldn't report only those
error_reporting(E_WARNING | E_NOTICE);

errors will be logged by default by php, normally in a error.log file at the same level than the running script.

in development environment, one can also show them on screen:

ini_set('display_errors', 1);

in production however, one should

ini_set('display_errors', 0);

and show a friendly problem message through the use of an Exception or Error handler.