PHP error types and levels

Introduction

Errors in PHP tell you when something goes wrong in your code. Knowing error types helps you fix problems faster.

When you want to find out why your PHP script stopped working.

When you want to show or hide certain errors during development or on a live website.

When you want to log errors to a file for later review.

When you want to handle different errors differently in your code.

When you want to improve your website's stability by catching mistakes early.

Syntax

PHP

<?php
// Example to set error reporting level
error_reporting(E_ALL);
// Turn on displaying errors
ini_set('display_errors', '1');
?>

error_reporting() sets which errors PHP will report.

ini_set('display_errors', '1') turns on showing errors on the screen.

Examples

This sets PHP to report only errors, warnings, and parse errors.

PHP

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

This reports all errors except notices, which are minor warnings.

PHP

<?php
error_reporting(E_ALL & ~E_NOTICE);
?>

This turns off showing errors on the screen, useful for live sites.

PHP

<?php
ini_set('display_errors', '0');
?>

Sample Program

This program turns on all error reporting and displays errors. It then causes a warning by trying to include a file that does not exist and a notice by using a variable that was never set.

PHP

<?php
// Turn on all error reporting
error_reporting(E_ALL);
ini_set('display_errors', '1');

// Trigger a warning by including a missing file
include('missingfile.php');

// Trigger a notice by using an undefined variable
echo $undefinedVar;
?>

Important Notes

Errors have different levels: E_ERROR (fatal), E_WARNING (non-fatal), E_NOTICE (minor).

Use error_reporting() to control which errors you want to see.

On live sites, it's safer to hide errors from users and log them instead.

Summary

PHP errors help you find and fix problems in your code.

You can control which errors to show using error_reporting().

Displaying errors is useful during development but should be off on live sites.

Practice

1. Which PHP error type indicates a problem that stops the script from running?

easy

A. Warning

B. Fatal error

C. Notice

D. Deprecated

Solution

1. Step 1: Understand PHP error types

   Fatal errors are serious problems that stop the script immediately.

2. Step 2: Compare with other error types

   Warnings and notices do not stop the script; deprecated warns about old code.

3. Final Answer:

   Fatal error -> Option B

4. Quick Check:

   Fatal error = stops script [OK]

Hint: Fatal errors stop scripts immediately, others do not [OK]

Common Mistakes:

• Confusing warnings with fatal errors
• Thinking notices stop script execution
• Mixing deprecated warnings with fatal errors

2. Which of the following is the correct way to set PHP to report all errors except notices?

easy

A. error_reporting(E_ALL & ~E_NOTICE);

B. error_reporting(E_ALL | E_NOTICE);

C. error_reporting(E_ALL & E_NOTICE);

D. error_reporting(E_ALL ^ E_NOTICE);

Solution

1. Step 1: Understand error_reporting flags

   E_ALL means all errors; ~E_NOTICE means exclude notices using bitwise NOT.

2. Step 2: Analyze each option

   error_reporting(E_ALL & ~E_NOTICE); uses bitwise AND with NOT (~) to exclude notices correctly.

3. Final Answer:

   error_reporting(E_ALL & ~E_NOTICE); -> Option A

4. Quick Check:

   Exclude notices with & ~E_NOTICE [OK]

Hint: Use & ~E_NOTICE to exclude notices from all errors [OK]

Common Mistakes:

• Using | instead of & ~ to exclude errors
• Confusing ^ (XOR) with exclusion
• Using & E_NOTICE which includes only notices

3. What will be the output of this PHP code?

<?php
error_reporting(E_ERROR | E_WARNING);
echo $undefined_variable;
include('missing_file.php');
?>

medium

A. Warning about missing file only

B. Fatal error about missing file

C. Notice about undefined variable and warning about missing file

D. No output, script runs silently

Solution

1. Step 1: Check error_reporting level

   Only E_ERROR and E_WARNING are reported; notices are not shown.

2. Step 2: Analyze code behavior

   Undefined variable triggers a notice (not shown). Missing file triggers a warning (shown).

3. Final Answer:

   Warning about missing file only -> Option A

4. Quick Check:

   E_WARNING shown, notices hidden [OK]

Hint: Only errors and warnings show; notices are hidden [OK]

Common Mistakes:

• Expecting notice output when it's excluded
• Confusing warning with fatal error
• Thinking script stops on warning

4. Identify the error in this PHP code snippet:

<?php
error_reporting(E_ALL);
ini_set('display_errors', 0);
echo $undefined_var;
?>

medium

A. Errors will be displayed despite display_errors set to 0

B. No errors will be reported because error_reporting is off

C. Syntax error due to missing semicolon

D. Errors are reported but not displayed due to display_errors=0

Solution

1. Step 1: Understand error_reporting and display_errors

   error_reporting(E_ALL) enables all error reporting; display_errors=0 hides errors from output.

2. Step 2: Analyze code behavior

   Errors are logged/reported internally but not shown on screen because display_errors is off.

3. Final Answer:

   Errors are reported but not displayed due to display_errors=0 -> Option D

4. Quick Check:

   display_errors=0 hides errors, reporting still active [OK]

Hint: display_errors=0 hides errors; error_reporting controls reporting [OK]

Common Mistakes:

• Thinking errors won't be reported at all
• Confusing display_errors with error_reporting
• Assuming syntax error due to missing semicolon

5. You want to show all errors except deprecated warnings during development but hide all errors on the live site. Which code setup achieves this best?

hard

A. error_reporting(E_ALL); ini_set('display_errors', 1);

B. error_reporting(E_ALL & ~E_NOTICE); ini_set('display_errors', 0);

C. if (ENV == 'dev') { error_reporting(E_ALL & ~E_DEPRECATED); ini_set('display_errors', 1); } else { error_reporting(0); ini_set('display_errors', 0); }

D. if (ENV == 'prod') { error_reporting(E_ALL); ini_set('display_errors', 1); } else { error_reporting(0); ini_set('display_errors', 0); }

Solution

1. Step 1: Understand environment-based error settings

   During development (dev), show all errors except deprecated; on live (prod), hide all errors.

2. Step 2: Analyze each option

   if (ENV == 'dev') { error_reporting(E_ALL & ~E_DEPRECATED); ini_set('display_errors', 1); } else { error_reporting(0); ini_set('display_errors', 0); } correctly uses error_reporting with exclusion and display_errors on dev, off on live.

3. Final Answer:

   if (ENV == 'dev') { error_reporting(E_ALL & ~E_DEPRECATED); ini_set('display_errors', 1); } else { error_reporting(0); ini_set('display_errors', 0); } -> Option C

4. Quick Check:

   Dev shows errors except deprecated; live hides all [OK]

Hint: Use environment check to toggle error reporting and display [OK]

Common Mistakes:

• Showing errors on live site
• Not excluding deprecated warnings during dev
• Confusing environment variable names