How to catch undefined functions with set_error_handler in PHP

Question

I'm taking the leap: my PHP scripts will ALL fail gracefully!

At least, that's what I'm hoping for...`

I don't want to wrap (practically) every single line in try...catch statements, so I think my best bet is to make a custom error handler for the beginning of my files.

I'm testing it out on a practice page:

function customError($level,$message,$file,$line,$context) {
    echo "Sorry, an error has occured on line $line.<br />";
    echo "The function that caused the error says $message.<br />";
    die();
}

set_error_handler("customError");

echo($imAFakeVariable);

This works fine, returning:

Sorry, an error has occurred on line 17. The function that caused the error says Undefined variable: imAFakeVariable.

However, this setup doesn't work for undefined functions.

function customError($level,$message,$file,$line,$context) {
    echo "Sorry, an error has occured on line $line.<br />";
    echo "The function that caused the error says $message.<br />";
    die();
}

set_error_handler("customError");

imAFakeFunction();

This returns:

Fatal error: Call to undefined function: imafakefunction() in /Library/WebServer/Documents/experimental/errorhandle.php on line 17

Why isn't my custom error handler catching undefined functions? Are there other problems that this will cause?

Answer 1

I guess you needs to use register_shutdown_function also

For example:

 register_shutdown_function( array( $this, 'customError' ));.

   function customError() 
   {

     $arrStrErrorInfo = error_get_last();

     print_r( $arrStrErrorInfo );

   }

Answer 2

set_error_handler is designed to handle errors with codes of: E_USER_ERROR | E_USER_WARNING | E_USER_NOTICE. This is because set_error_handler is meant to be a method of reporting errors thrown by the user error function trigger_error.

However, I did find this comment in the manual that may help you:

"The following error types cannot be handled with a user defined function: E_ERROR, E_PARSE, E_CORE_ERROR, E_CORE_WARNING, E_COMPILE_ERROR, E_COMPILE_WARNING, and most of E_STRICT raised in the file where set_error_handler() is called."

This is not exactly true. set_error_handler() can't handle them, but ob_start() can handle at least E_ERROR.

<?php

function error_handler($output)
{
    $error = error_get_last();
    $output = "";
    foreach ($error as $info => $string)
        $output .= "{$info}: {$string}\n";
    return $output;
}

ob_start('error_handler');

will_this_undefined_function_raise_an_error();

?>

Really though these errors should be silently reported in a file, for example. Hopefully you won't have many E_PARSE errors in your project! :-)

As for general error reporting, stick with Exceptions (I find it helpful to make them tie in with my MVC system). You can build a pretty versatile Exception to provide options via buttons and add plenty of description to let the user know what's wrong.

Answer 3

From the documentation (emphasis added):

The following error types cannot be handled with a user defined function: E_ERROR, E_PARSE, E_CORE_ERROR, E_CORE_WARNING, E_COMPILE_ERROR, E_COMPILE_WARNING, and most of E_STRICT raised in the file where set_error_handler() is called.

Calling undefined functions triggers an E_ERROR, thus it can not be handled by the error callback (or by exception handlers for that matter). All that you can do is set error_reporting to 0.

PS, if you are rolling your own error handler, you should take care to handle correctly the @ operator. From the documentation (emphasis added):

It is important to remember that the standard PHP error handler is completely bypassed. error_reporting() settings will have no effect and your error handler will be called regardless - however you are still able to read the current value of error_reporting and act appropriately. Of particular note is that this value will be 0 if the statement that caused the error was prepended by the @ error-control operator.

Answer 4

Why isn't my custom error handler catching undefinedd functions? Are there other problems that this will cause?

At a guess, I'd say that undefined function errors travel through a different execution path than other error types. Perhaps the PHP designers could tell you more, except I doubt PHP is in any way designed.

If you'd like your scripts to fail gracefully while still writing them PHP-style, try putting the entire page in a function and then call it within a try..catch block.