About php : How-can-I-get-useful-error-messages-in-PHP

Question Detail

Quite often I will try and run a PHP script and just get a blank screen back. No error message; just an empty screen. The cause might have been a simple syntax error (wrong bracket, missing semicolon), or a failed function call, or something else entirely.

It is very difficult to figure out what went wrong. I end up commenting out code, entering “echo” statements everywhere, etc. trying to narrow down the problem. But there surely must be a better way, right?

Is there a way to get PHP to produce a useful error message, like Java does?

Question Answer

For syntax errors, you need to enable error display in the php.ini. By default these are turned off because you don’t want a “customer” seeing the error messages. Check this page in the PHP documentation for information on the 2 directives: error_reporting and display_errors. display_errors is probably the one you want to change. If you can’t modify the php.ini, you can also add the following lines to an .htaccess file:

php_flag display_errors on
php_value error_reporting 2039

You may want to consider using the value of E_ALL (as mentioned by Gumbo) for your version of PHP for error_reporting to get all of the errors. more info

3 other items: (1) You can check the error log file as it will have all of the errors (unless logging has been disabled). (2) Adding the following 2 lines will help you debug errors that are not syntax errors:

error_reporting(-1);
ini_set(‘display_errors’, ‘On’);

(3) Another option is to use an editor that checks for errors when you type, such as PhpEd. PhpEd also comes with a debugger which can provide more detailed information. (The PhpEd debugger is very similar to xdebug and integrates directly into the editor so you use 1 program to do everything.)

Cartman’s link is also very good: http://www.ibm.com/developerworks/library/os-debug/
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The following enables all errors:

ini_set(‘display_startup_errors’, 1);
ini_set(‘display_errors’, 1);
error_reporting(-1);

Also see the following links

http://php.net/manual/en/errorfunc.configuration.php#ini.display-errors
http://php.net/manual/en/errorfunc.configuration.php#ini.display-startup-errors
http://php.net/manual/en/function.error-reporting.php

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The following code should display all errors:

‘E_ERROR’,
0x0002 => ‘E_WARNING’,
0x0004 => ‘E_PARSE’,
0x0008 => ‘E_NOTICE’,
0x0010 => ‘E_CORE_ERROR’,
0x0020 => ‘E_CORE_WARNING’,
0x0040 => ‘E_COMPILE_ERROR’,
0x0080 => ‘E_COMPILE_WARNING’,
0x0100 => ‘E_USER_ERROR’,
0x0200 => ‘E_USER_WARNING’,
0x0400 => ‘E_USER_NOTICE’,
0x0800 => ‘E_STRICT’,
0x1000 => ‘E_RECOVERABLE_ERROR’,
0x2000 => ‘E_DEPRECATED’,
0x4000 => ‘E_USER_DEPRECATED’
);

if(!@is_string($name = @array_search($type, @array_flip($_ERRORS))))
{
$name = ‘E_UNKNOWN’;
};

return(print(@sprintf(“%s Error in file \xBB%s\xAB at line %d: %s\n”, $name, @basename($file), $line, $message)));
};

$old_error_handler = set_error_handler(“ErrorHandler”);

// other php code

?>

The only way to generate a blank page with this code is when you have a error in the shutdown handler. I copied and pasted this from my own cms without testing it, but I am sure it works.
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You can include the following lines in the file you want to debug:

error_reporting(E_ALL);
ini_set(‘display_errors’, ‘1’);

This overrides the default settings in php.ini, which just make PHP report the errors to the log.
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Errors and warnings usually appear in ….\logs\php_error.log or ….\logs\apache_error.log depending on your php.ini settings.

Also useful errors are often directed to the browser, but as they are not valid html they are not displayed.

So “tail -f” your log files and when you get a blank screen use IEs “view” -> “source” menu options to view the raw output.
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PHP Configuration

2 entries in php.ini dictate the output of errors:

display_errors
error_reporting

In production, display_errors is usually set to Off (Which is a good thing, because error display in production sites is generally not desirable!).

However, in development, it should be set to On, so that errors get displayed. Check!

error_reporting (as of PHP 5.3) is set by default to E_ALL & ~E_NOTICE & ~E_STRICT & ~E_DEPRECATED (meaning, everything is shown except for notices, strict standards and deprecation notices). When in doubt, set it to E_ALL to display all the errors. Check!

Whoa whoa! No check! I can’t change my php.ini!

That’s a shame. Usually shared hosts do not allow the alteration of their php.ini file, and so, that option is sadly unavailable. But fear not! We have other options!

Runtime configuration

In the desired script, we can alter the php.ini entries in runtime! Meaning, it’ll run when the script runs! Sweet!

error_reporting(E_ALL);
ini_set(“display_errors”, “On”);

These two lines will do the same effect as altering the php.ini entries as above! Awesome!

I still get a blank page/500 error!

That means that the script hadn’t even run! That usually happens when you have a syntax error!

With syntax errors, the script doesn’t even get to runtime. It fails at compile time, meaning that it’ll use the values in php.ini, which if you hadn’t changed, may not allow the display of errors.

Error logs

In addition, PHP by default logs errors. In shared hosting, it may be in a dedicated folder or on the same folder as the offending script.

If you have access to php.ini, you can find it under the error_log entry.
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I’m always using this syntax at the very top of the php script.

ini_set(‘error_reporting’, E_ALL);
ini_set(‘display_errors’, ‘On’); //On or Off

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There is a really useful extension called “xdebug” that will make your reports much nicer as well.
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For quick, hands-on troubleshooting I normally suggest here on SO:

error_reporting(~0); ini_set(‘display_errors’, 1);

to be put at the beginning of the script that is under trouble-shooting. This is not perfect, the perfect variant is that you also enable that in the php.ini and that you log the errors in PHP to catch syntax and startup errors.

The settings outlined here display all errors, notices and warnings, including strict ones, regardless which PHP version.

Next things to consider:

Install Xdebug and enable remote-debugging with your IDE.

See as well:

Error Reporting (PHP The Right Way.)
Predefined ConstantsDocs
error_reporting()Docs
display_errorsDocs

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It is possible to register an hook to make the last error or warning visible.

function shutdown(){
var_dump(error_get_last());
}

register_shutdown_function(‘shutdown’);

adding this code to the beginning of you index.php will help you debug the problems.
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If you are super cool, you might try:

$test_server = $_SERVER[‘SERVER_NAME’] == “127.0.0.1” || $_SERVER[‘SERVER_NAME’] == “localhost” || substr($_SERVER[‘SERVER_NAME’],0,3) == “192”;

ini_set(‘display_errors’,$test_server);
error_reporting(E_ALL|E_STRICT);

This will only display errors when you are running locally. It also gives you the test_server variable to use in other places where appropriate.

Any errors that happen before the script runs won’t be caught, but for 99% of errors that I make, that’s not an issue.
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On the top of the page choose a parameter

error_reporting(E_ERROR | E_WARNING | E_PARSE);

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This is a problem of loaded vs. runtime configuration
It’s important to recognize that a syntax error or parse error happens during the compile or parsing step, which means that PHP will bail before it’s even had a chance to execute any of your code. So if you are modifying PHP’s display_errors configuration during runtime, (this includes anything from using ini_set in your code to using .htaccess, which is a runtime configuration file) then only the default loaded configuration settings are in play.
How to always avoid WSOD in development
To avoid a WSOD you want to make sure that your loaded configuration file has display_errors on and error_reporting set to -1 (this is the equivalent E_ALL because it ensures all bits are turned on regardless of which version of PHP you’re running). Don’t hardcode the constant value of E_ALL, because that value is subject to change between different versions of PHP.
Loaded configuration is either your loaded php.ini file or your apache.conf or httpd.conf or virtualhost file. Those files are only read once during the startup stage (when you first start apache httpd or php-fpm, for example) and only overridden by runtime configuration changes. Making sure that display_errors = 1 and error_reporting = -1 in your loaded configuration file ensures that you will never see a WSOD regardless of syntax or parse error that occur before a runtime change like ini_set(‘display_errors’, 1); or error_reporting(E_ALL); can take place.
How to find your (php.ini) loaded configuration files
To locate your loaded configuration file(s) just create a new PHP file with only the following code…
“);
ini_set ( “error_append_string”, “