PHP set_error_handler() always returns null

Question

I can't work out what's going wrong.

The following always results in outputting "Could not set an error handler":

<?php

function die_on_error($errno, $errstr, $errfile, $errline, $errcontext){
    echo "\n\nThere was an error. Today is a good day to die.";
    echo "\n\n\$errno: $errno";
    echo "\n\n\$errstr: $errstr";
    echo "\n\n\$errfile: $errfile";
    echo "\n\n\$errline: $errline";
    echo "\n\n\$errcontext: ";
    var_dump($errcontext);
    die();
}

if (is_null(set_error_handler('die_on_error'))){
    die("\n\nCould not set an error handler.");
}

Are you actually generating an error?

Source Matters
– Source Matters

2015-08-11 04:04:44 +00:00
Commented Aug 11, 2015 at 4:04 — Source Matters
– Source Matters, Commented Aug 11, 2015 at 4:04
try with ob_start('die_on_error');

Abdulla Nilam
– Abdulla Nilam

2015-08-11 04:27:14 +00:00
Commented Aug 11, 2015 at 4:27 — Abdulla Nilam
– Abdulla Nilam, Commented Aug 11, 2015 at 4:27

Mayank K. Swami · Accepted Answer · 2015-08-11 04:44:52Z

3

Because you need to have an error to execute this function,If errors occur before the script is executed the custom error handler cannot be called since it is not registered at that time.

function die_on_error($errno, $errstr, $errfile, $errline, $errcontext){
    echo"This is sparta";
    echo "\n\n\$errno: $errno";
    echo "\n\n\$errstr: $errstr";
    echo "\n\n\$errfile: $errfile";
    echo "\n\n\$errline: $errline";
    echo "\n\n\$errcontext: ";
    var_dump($errcontext);
    die();
}

 print_r(set_error_handler('die_on_error'));

trigger_error("Incorrect  array", E_USER_WARNING);

demo

edited Aug 11, 2015 at 4:44

answered Aug 11, 2015 at 4:37

Mayank K. Swami

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3 Comments

Jayy Over a year ago

Great, it works. But I don't get it! Firstly, in both your code, die_on_error is defined before the call to set_error_handler. Secondly, in both cases, no error occurs before set_error_handler. confused

Jayy Over a year ago

Aaah I was being really stupid. set_error_handler returns null even if you have successfully set a custom error handler, if the previous error handler was the PHP default. The only time it wouldn't return null is if you replace a custom error handler with something else

Mayank K. Swami Over a year ago

exactly ... you got it before my comment, nice R&D :D

user3318924 · Accepted Answer · 2016-03-17 20:03:00Z

I have a complicated singleton class for handling errors, but I also like to know that all has worked ok.

My solution was to silence error reporting and trigger an error with a specific string to check for then set a variable within the class to true and check against that.

something like

class myerror
{
    private $enabled;

    public function __construct()
    {
       if ($this->set_handler() === false) die('Error Handler Failed To Init...');
    }

    private function set_handler()
    {
        $methodVariable = array('myerror', 'error_handler');
        if (is_callable($methodVariable, true, $callable_name) === false return false;
        @set_error_handler($callable_name, E_ALL);
        trigger_error('Error Init', E_USER_NOTICE);
        return $this->enabled;
    }

    public static function error_handler($errNo, $errStr, $errFile, $errLine)
    {
        if($errStr == 'Error Init')
        {
            $this->enabled = true;
            return;
        }
        // do something with the error
    }
}

This is just a non tested example but I hope it gives you some idea how I solved the problem. :)

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