error_reporting

If you just see a blank page instead of an error reporting and you have no server access so you can't edit php configuration files like php.ini try this:

- create a new file in which you include the faulty script:

<?php
 error_reporting(E_ALL);
 ini_set("display_errors", 1);
 include("file_with_errors.php");
?>

- execute this file instead of the faulty script file 

now errors of your faulty script should be reported.
this works fine with me. hope it solves your problem as well!

The example of E_ALL ^ E_NOTICE is a 'bit' confusing for those of us not wholly conversant with bitwise operators.

If you wish to remove notices from the current level, whatever that unknown level might be, use & ~ instead:

<?php
//....
$errorlevel=error_reporting();
error_reporting($errorlevel & ~E_NOTICE);
//...code that generates notices
error_reporting($errorlevel);
//...
?>

^ is the xor (bit flipping) operator and would actually turn notices *on* if they were previously off (in the error level on its left). It works in the example because E_ALL is guaranteed to have the bit for E_NOTICE set, so when ^ flips that bit, it is in fact turned off. & ~ (and not) will always turn off the bits specified by the right-hand parameter, whether or not they were on or off.

Under PHP 8.0, error_reporting() does not return 0 when then the code uses a @ character.  

For example

<?php

$a=$array[20]; // error_reporting() returns 0 in php <8 and 4437 in PHP>=8

?>

It could save two minutes to someone:
E_ALL & ~E_NOTICE  integer value is 6135

Note that E_NOTICE will warn you about uninitialized variables, but assigning a key/value pair counts as initialization, and will not trigger any error :
<?php
error_reporting(E_ALL);

$foo = $bar; //notice : $bar uninitialized

$bar['foo'] = 'hello'; // no notice, although $bar itself has never been initialized (with "$bar = array()" for example)

$bar = array('foobar' => 'barfoo');
$foo = $bar['foobar'] // ok

$foo = $bar['nope'] // notice : no such index
?>

The error_reporting() function will return 0 if error suppression is currently active somewhere in the call tree (via the @ operator).

error_reporting(E_ALL);
if (!ini_get('display_errors')) {
    ini_set('display_errors', '1');
}

In php7,  what was generally a notice or a deprecated is now a warning : the same level of a mysql error …  unacceptable for me.

I do have dozen of old projects and I surely d'ont want to define every variable which I eventually wrote 20y ago.

So two option: let php7 degrade my expensive SSDs writing Gb/hours or implement smthing like server level monitoring ( with auto_[pre-ap]pend_file in php.ini) and turn off E_WARNING

Custom overriding the level of php errors should be super handy and flexible …

Some E_STRICT errors seem to be thrown during the page's compilation process.  This means they cannot be disabled by dynamically altering the error level at run time within that page.

The work-around for this was to rename the file and replace the original with a error_reporting() call and then a require() call.

Ex, rename index.php to index.inc.php, then re-create index.php as:

<?php
error_reporting(E_ALL & ~(E_STRICT|E_NOTICE));
require('index.inc.php');
?>

That allows you to alter the error reporting prior to the file being compiled.

I discovered this recently when I was given code from another development firm that triggered several E_STRICT errors and I wanted to disable E_STRICT on a per-page basis.

I had the problem that if there was an error, php would just give me a blank page.  Any error at all forced a blank page instead of any output whatsoever, even though I made sure that I had error_reporting set to E_ALL, display_errors turned on, etc etc.  But simply running the file in a different directory allowed it to show errors!

Turns out that the error_log file in the one directory was full (2.0 Gb).  I erased the file and now errors are displayed normally.  It might also help to turn error logging off.

https://techysupport.co/norton-tech-support/

The error_reporting() function won't be effective if your display_errors directive in php.ini is set to "Off", regardless of level reporting you set. I had to set

display_errors = On
error_reporting = ~E_ALL

to keep no error reporting as default, but be able to change error reporting level in my scripts.
I'm using PHP 4.3.9 and Apache 2.0.

error_reporting() has no effect if you have defined your own error handler with set_error_handler()

[Editor's Note: This is not quite accurate.

E_ERROR, E_PARSE, E_CORE_ERROR, E_CORE_WARNING, E_COMPILE_ERROR and E_COMPILE_WARNING error levels will be handled as per the error_reporting settings.

All other levels of errors will be passed to the custom error handler defined by set_error_handler().

Zeev Suraski suggests that a simple way to use the defined levels of error reporting with your custom error handlers is to add the following line to the top of your error handling function:

if (!($type & error_reporting())) return;

 -zak@php.net]

If you get a weird mysql warnings like "Warning: mysql_query() : Your query requires a full tablescan...", don't look for error_reporting settings - it's set in php.ini.
You can turn it off with
ini_set("mysql.trace_mode","Off");
in your script
http://tinymy.link/mctct

It might be a good idea to include E_COMPILE_ERROR in error_reporting. 

If you have a customer error handler that does not output warnings, you may get a white screen of death if a "require" fails.

Example:
<?php 
  error_reporting(E_ERROR | E_WARNING | E_PARSE);

  function myErrorHandler($errno, $errstr, $errfile, $errline) {
    // Do something other than output message.
    return true;
  }

  $old_error_handler = set_error_handler("myErrorHandler");

  require "this file does not exist";
?>

To prevent this, simply include E_COMPILE_ERROR in the error_reporting.

<?php
  error_reporting(E_ERROR | E_WARNING | E_PARSE | E_COMPILE_ERROR);
?>

Only display php errors to the developer...