How to get useful error messages in PHP?

Question

I find programming in PHP quite frustrating. Quite often I will try and run the script and just get a blank screen back. No error message, just 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?.

So, is there a way to get PHP to produce useful error message like Java does? Can anyone recommend good PHP debugging tips, tools and techniques?

Answer 1

In addition to all the wonderful answers here, I'd like to throw in a special mention for the MySQLi and PDO libraries.

In order to...

1. Always see database related errors, and
2. Avoid checking the return types for methods to see if something went wrong

The best option is to configure the libraries to throw exceptions.

MySQLi

Add this near the top of your script

mysqli_report(MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT);

This is best placed before you use new mysqli() or mysqli_connect().

PDO

Set the PDO::ATTR_ERRMODE attribute to PDO::ERRMODE_EXCEPTION on your connection instance. You can either do this in the constructor

$pdo = new PDO('driver:host=localhost;...', 'username', 'password', [
    PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION
]);

or after creation

$pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

Answer 2

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 Constants^Docs
• error_reporting()^Docs
• display_errors^Docs

Answer 3

if you are a ubuntu user then goto your terminal and run this command

sudo tail -50f /var/log/apache2/error.log

where it will display recent 50 errors. There is a error file error.log for apache2 which logs all the errors.

Answer 4

PHP Configuration

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

1. display_errors
2. 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.

Answer 5

My usual problem are "little, stupid" parser errors which unfortunately do not show up.

However, when a .PHP-File includes a file that has parser-errors, they are shown! So I had the idea of writing a little "executor-script" that is launched with the name of the buggy file as argument, i.e. example.com/sx.php?sc=buggy.php

It had already saved me from a lot of headache, maybe it will be helpful to someone else, too :)

sx.php

$sc = $_GET["sc"];
if ((!isset($_GET["sc"]) && empty($_GET["sc"]))) {
    echo "Please select file to execute using ?sc= (you may omit the .PHP-extension)";
} else {
    $sc = $_GET["sc"];
    if (false==stripos('.php',$sc)) $sc.='.php';  // adjust this if your preferred extension is php5!
    require($sc);
}
?>

Answer 6

error_reporting(E_ALL | E_STRICT);

And turn on display errors in php.ini