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How can I get useful error messages in PHP?

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?

@JuannStrauss, That's understating it. And when you finally see the errors, it says T_PAAMAYIM_NEKUDOTAYIM. Or maybe "must be an instance of integer, integer given".
If you have a parse error none of these will work on many web hosts, and you might not have access to the error logs. You will need to install php on your local machine (XAMPP on Windows etc) and do a command line synax check php.exe -l <your file name>

S
Sumurai8

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/


2039 is the value of E_ERROR | E_WARNING | E_PARSE | E_CORE_ERROR | E_CORE_WARNING | E_COMPILE_ERROR | E_COMPILE_WARNING | E_USER_ERROR | E_USER_WARNING | E_USER_NOTICE. See docs.php.net/manual/en/errorfunc.constants.php
I like the option of .htaccess file. It helps me debug in an area that is not part of the public website. Thanks a lot for this tip!
I would add that logging errors to file (and looking them up there) is the best solution. Don't rely on displaying errors on-page - they can ruin it, you can forget to turn error reporting for production site and this will cause you trouble in future
J
Janyk

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


Best to make these changes at the .ini file level. Turning on error reporting from within a script is useless, as it won't help with syntax errors or other fatal errors that kill the compile phase. The script gets killed long before it begins executing and reaches the reporting overrides.
You are correct indeed. I did not notice that the move is to your own server.
Run phpinfo() to find the correct php.ini file. Look for the Loaded Configuration File line.
If you are looking for errors that occur during the compile phase, check your apache logs often located at /var/log/apache2/error.log
This answer will fail on php7 when strict typing is enabled, because the second parameter of ini_set is a string.
m
m4dm4x1337

The following code should display all errors:

<?php

// ----------------------------------------------------------------------------------------------------
// - Display Errors
// ----------------------------------------------------------------------------------------------------
ini_set('display_errors', 'On');
ini_set('html_errors', 0);

// ----------------------------------------------------------------------------------------------------
// - Error Reporting
// ----------------------------------------------------------------------------------------------------
error_reporting(-1);

// ----------------------------------------------------------------------------------------------------
// - Shutdown Handler
// ----------------------------------------------------------------------------------------------------
function ShutdownHandler()
{
    if(@is_array($error = @error_get_last()))
    {
        return(@call_user_func_array('ErrorHandler', $error));
    };

    return(TRUE);
};

register_shutdown_function('ShutdownHandler');

// ----------------------------------------------------------------------------------------------------
// - Error Handler
// ----------------------------------------------------------------------------------------------------
function ErrorHandler($type, $message, $file, $line)
{
    $_ERRORS = Array(
        0x0001 => '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.


I get a blank page from that code. What do you mean by "you have a error in the shutdown handler" and what should I do to solve the problem?
@PaoloM, He is saying an error in the function ShutdownHandler above. Basically this is a stopgap hack in place of proper error handling.
Thanks, was useful, but how can I disable E_NOTICE errors in this function?
This is the right solution, but be careful with information discosure when error occurs... (prefer logging instead of echoing to users)
I am using this when the Symfony can't catch correctly fatal errors.
T
Tomalak

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.


That's true. In this case the values must be set in the ini directly -- for a pure development environment this may be preferable anyway.
J
Jens

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.


Sadly, view page source displays nothing too.
Parse errors should be visible in the Apache's error log, regardless of what setting you have anywhere else. If you don't have control over the server then getting the apache error log might be difficult, but I suggest you talk with your provider and there are ways to expose the error log to you. Other then that, I can only suggest what other have - vet your code for parsing errors in your local development server before you deploy to production. Also, a validating IDE such as Eclipse's PDT might be of great help.
Coming back to this, I recently had a stack overflow issue that wasn't generating any errors, even in the logs and didn't manifest itself as such till I installed xdebug into the server. Gah.
If you cannot modify php.ini, create a .htaccess file with php_flag display_errors 1 in it.
m
mario

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.


For the runtime configuration, you may be able to put those lines into a separate file & include the php file with the error.
F
FDisk

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

I'm sorry, but -1 for not reading the other answers already posted. This is taken care of in the .htaccess as already mentioned several times.
usual "free hosting" ignores the .htaccess
g
gnarf

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


Indeed, this is a very useful debugging tool—makes error messages much more verbose, with full stack traces and variable dumps and everything.
Yes. And then use something like the VimDebugger plugin to step through your code and find out where it goes wrong.
NetBeans with xdebug here. It's so awesome. I'm new to PHP (usually ASP.NET) and had been issuing echo statements before.
h
hakre

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


E
Eduardo Oliveira

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.


This is pure gold for people who got stuck in webhosts that shows no error but allows zero log access
R
Rich Bradshaw

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.


If you're differentiating between local and production environments, you should simply enable or disable errors globally (in your php.ini) and not in code that can also be production code. If you need to debug a production website in its production environment and only want you to be able to view the errors, use $_SERVER['REMOTE_HOST'] to check whether the client is, well, you.
K
Kld

On the top of the page choose a parameter

error_reporting(E_ERROR | E_WARNING | E_PARSE);

C
Community

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...

<?php
phpinfo();

Then point your browser there and look at Loaded Configuration File and Additional .ini files parsed, which are usually at the top of your phpinfo() and will include the absolute path to all your loaded configuration files.

If you see (none) instead of the file, that means you don't have a php.ini in Configuration File (php.ini) Path. So you can download the stock php.ini bundled with PHP from here and copy that to your configuration file path as php.ini then make sure your php user has sufficient permissions to read from that file. You'll need to restart httpd or php-fpm to load it in. Remember, this is the development php.ini file that comes bundled with the PHP source. So please don't use it in production!

Just don't do this in production

This really is the best way to avoid a WSOD in development. Anyone suggesting that you put ini_set('display_errors', 1); or error_reporting(E_ALL); at the top of your PHP script or using .htaccess like you did here, is not going to help you avoid a WSOD when a syntax or parse error occurs (like in your case here) if your loaded configuration file has display_errors turned off.

Many people (and stock installations of PHP) will use a production-ini file that has display_errors turned off by default, which typically results in this same frustration you've experienced here. Because PHP already has it turned off when it starts up, then encounters a syntax or parse error, and bails with nothing to output. You expect that your ini_set('display_errors',1); at the top of your PHP script should have avoided that, but it won't matter if PHP can't parse your code because it will never have reached the runtime.


s
sjas

To persist this and make it confortale, you can edit your php.ini file. It is usually stored in /etc/php.ini or /etc/php/php.ini, but more local php.ini's may overwrite it, depending on your hosting provider's setup guidelines. Check a phpinfo() file for Loaded Configuration File at the top, to be sure which one gets loaded last.

Search for display_errors in that file. There should be only 3 instances, of which 2 are commented.

Change the uncommented line to:

display_errors = stdout

A
Abuzer Firdousi
ini_set('display_errors', 1);
ini_set('display_startup_errors', 1);
error_reporting(E_ALL);

p
peterh

I don't know if it will help, but here is a piece of my standard config file for php projects. I tend not to depend too much on the apache configs even on my own server.

I never have the disappearing error problem, so perhaps something here will give you an idea.

Edited to show APPLICATON_LIVE

/*
APPLICATION_LIVE will be used in process to tell if we are in a development or production environment.  It's generally set as early as possible (often the first code to run), before any config, url routing, etc.
*/

if ( preg_match( "%^(www.)?livedomain.com$%", $_SERVER["HTTP_HOST"]) ) {
    define('APPLICATION_LIVE', true);
} elseif ( preg_match( "%^(www.)?devdomain.net$%", $_SERVER["HTTP_HOST"]) ) {
    define('APPLICATION_LIVE', false);
} else {
    die("INVALID HOST REQUEST (".$_SERVER["HTTP_HOST"].")");
    // Log or take other appropriate action.
}


/*
--------------------------------------------------------------------
DEFAULT ERROR HANDLING
--------------------------------------------------------------------
Default error logging.  Some of these may be changed later based on APPLICATION_LIVE.
*/
error_reporting(E_ALL & ~E_STRICT);
ini_set ( "display_errors", "0");
ini_set ( "display_startup_errors", "0");
ini_set ( "log_errors", 1);
ini_set ( "log_errors_max_len", 0);
ini_set ( "error_log", APPLICATION_ROOT."logs/php_error_log.txt");
ini_set ( "display_errors", "0");
ini_set ( "display_startup_errors", "0");

if ( ! APPLICATION_LIVE ) {
    // A few changes to error handling for development.
    // We will want errors to be visible during development.
    ini_set ( "display_errors", "1");
    ini_set ( "display_startup_errors", "1");
    ini_set ( "html_errors", "1");
    ini_set ( "docref_root", "http://www.php.net/");
    ini_set ( "error_prepend_string", "<div style='color:red; font-family:verdana; border:1px solid red; padding:5px;'>");
    ini_set ( "error_append_string", "</div>");
}

@Eli, This has a runtime overhead though, per page request.
up 1 for the concept that overlook debug settings however server is configured, good while you are deploying or maintaining (under development)
J
Janyk
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.


Xdebug can be enable from php.ini
J
Janyk

I recommend Nette Tracy for better visualization of errors and exceptions in PHP:

https://i.stack.imgur.com/B1gSC.png


Tracy takes care about proper setting of all display errors and error reporting options to provide output in such situations as described in original post... So this tool is especially helpful for addressing asker "Can anyone recommend good PHP debugging tips, tools and techniques?".
Ó
Ólafur Waage
error_reporting(E_ALL | E_STRICT);

And turn on display errors in php.ini


s
soulmerge

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');

B
Brad Larson

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;
}

O
Otiel

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

display_errors = On

restart your server.


u
user1681048

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.


U
Unihedron

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.


D
Daniel Sorichetti

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.


As with Tomalak's answer, this doesn't work for syntax errors.
J
Janyk

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.


P
Phil

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);

A
Ayman Hourieh

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"

j
jmucchiello

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

m
mario

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.