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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/
……………………………………………………
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

……………………………………………………
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([email protected]_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.
……………………………………………………
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.
……………………………………………………
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.
……………………………………………………
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.
……………………………………………………
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

……………………………………………………
There is a really useful extension called “xdebug” that will make your reports much nicer as well.
……………………………………………………
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

……………………………………………………
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.
……………………………………………………
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.
……………………………………………………
On the top of the page choose a parameter

error_reporting(E_ERROR | E_WARNING | E_PARSE);

……………………………………………………
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”, “

“);
}

……………………………………………………
error_reporting(E_ALL | E_STRICT);
ini_set(‘display_errors’, 1);
ini_set(‘html_errors’, 1);

In addition, you can get more detailed information with xdebug.
……………………………………………………
I recommend Nette Tracy for better visualization of errors and exceptions in PHP:

……………………………………………………
error_reporting(E_ALL | E_STRICT);

And turn on display errors in php.ini
……………………………………………………
You can register your own error handler in PHP. Dumping all errors to a file might help you in these obscure cases, for example. Note that your function will get called, no matter what your current error_reporting is set to. Very basic example:

function dump_error_to_file($errno, $errstr) {
file_put_contents(‘/tmp/php-errors’, date(‘Y-m-d H:i:s – ‘) . $errstr, FILE_APPEND);
}
set_error_handler(‘dump_error_to_file’);

……………………………………………………
The two key lines you need to get useful errors out of PHP are:

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

As pointed out by other contributors, these are switched off by default for security reasons. As a useful tip – when you’re setting up your site it’s handy to do a switch for your different environments so that these errors are ON by default in your local and development environments. This can be achieved with the following code (ideally in your index.php or config file so this is active from the start):

switch($_SERVER[‘SERVER_NAME’])
{
// local
case ‘yourdomain.dev’:
// dev
case ‘dev.yourdomain.com’:
ini_set(‘display_errors’,1);
error_reporting(E_ALL);
break;
//live
case ‘yourdomain.com’:
//…
break;
}

……………………………………………………
open your php.ini,
make sure it’s set to:

display_errors = On

restart your server.
……………………………………………………
You might also want to try PHPStorm as your code editor. It will find many PHP and other syntax errors right as you are typing in the editor.
……………………………………………………
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.
……………………………………………………
To turn on full error reporting, add this to your script:

error_reporting(E_ALL);

This causes even minimal warnings to show up. And, just in case:

ini_set(‘display_errors’, ‘1’);

Will force the display of errors. This should be turned off in production servers, but not when you’re developing.
……………………………………………………
The “ERRORS” are the most useful things for the developers to know their mistakes and resolved them to make the system working perfect.

PHP provides some of better ways to know the developers why and where their piece of code is getting the errors, so by knowing those errors developers can make their code better in many ways.

Best ways to write following two lines on the top of script to get all errors messages:

error_reporting(E_ALL);
ini_set(“display_errors”, 1);

Another way to use debugger tools like xdebug in your IDE.
……………………………………………………
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…

Always see database related errors, and
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);

……………………………………………………
You can enable full error reporting (including notices and strict messages). Some people find this too verbose, but it’s worth a try. Set error_reporting to E_ALL | E_STRICT in your php.ini.

error_reporting = E_ALL | E_STRICT

E_STRICT will notify you about deprecated functions and give you recommendations about the best methods to do certain tasks.

If you don’t want notices, but you find other message types helpful, try excluding notices:

error_reporting = (E_ALL | E_STRICT) & ~E_NOTICE

Also make sure that display_errors is enabled in php.ini. If your PHP version is older than 5.2.4, set it to On:

display_errors = “On”

If your version is 5.2.4 or newer, use:

display_errors = “stderr”

……………………………………………………
Aside from error_reporting and the display_errors ini setting, you can get SYNTAX errors from your web server’s log files. When I’m developing PHP I load my development system’s web server logs into my editor. Whenever I test a page and get a blank screen, the log file goes stale and my editor asks if I want to reload it. When I do, I jump to the bottom and there is the syntax error. For example:

[Sun Apr 19 19:09:11 2009] [error] [client 127.0.0.1] PHP Parse error: syntax error, unexpected T_ENCAPSED_AND_WHITESPACE, expecting T_STRING or T_VARIABLE or T_NUM_STRING in D:\\webroot\\test\\test.php on line 9

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This answer is brought to you by the department of redundancy department.

ini_set() / php.ini / .htaccess / .user.ini

The settings display_errors and error_reporting have been covered sufficiently now. But just to recap when to use which option:

ini_set() and error_reporting() apply for runtime errors only.
php.ini should primarily be edited for development setups. (Webserver and CLI version often have different php.ini’s)
.htaccess flags only work for dated setups (Find a new hoster! Well managed servers are cheaper.)
.user.ini are partial php.ini’s for modern setups (FCGI/FPM)

And as crude alternative for runtime errors you can often use:

set_error_handler(“var_dump”); // ignores error_reporting and `@` suppression

error_get_last()

Can be used to retrieve the last runtime notice/warning/error, when error_display is disabled.
$php_errormsg

Is a superlocal variable, which also contains the last PHP runtime message.
isset() begone!

I know this will displease a lot of folks, but isset and empty should not be used by newcomers. You can add the notice suppression after you verified your code is working. But never before.

A lot of the “something doesn’t work” questions we get lately are the result of typos like:

if(isset($_POST[‘sumbit’]))
# ↑↑

You won’t get any useful notices if your code is littered with isset/empty/array_keys_exists. It’s sometimes more sensible to use @, so notices and warnings go to the logs at least.
assert_options(ASSERT_ACTIVE|ASSERT_WARNING);

To get warnings for assert() sections. (Pretty uncommon, but more proficient code might contain some.)

PHP7 requires zend.assertions=1 in the php.ini as well.
declare(strict_types=1);

Bending PHP into a strictly typed language is not going to fix a whole lot of logic errors, but it’s definitely an option for debugging purposes.
PDO / MySQLi

And @Phil already mentioned PDO/MySQLi error reporting options. Similar options exist for other database APIs of course.
json_last_error() + json_last_error_msg

For JSON parsing.
preg_last_error()

For regexen.
CURLOPT_VERBOSE

To debug curl requests, you need CURLOPT_VERBOSE at the very least.
shell/exec()

Likewise will shell command execution not yield errors on its own. You always need 2>&1 and peek at the $errno.

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