PHP error types and levels - Step-by-Step Execution

Concept Flow - PHP error types and levels

Start PHP script

↓

Code runs

↓

Error occurs?

No→Script continues

Yes↓

Identify error type

↓

Match error level

↓

Handle error (display/log/ignore)

↓

Script ends or continues

PHP runs code and checks if an error happens. If yes, it finds the error type and level, then handles it accordingly.

Execution Sample

PHP

<?php
// Trigger different error levels
trigger_error("Notice example", E_USER_NOTICE);
trigger_error("Warning example", E_USER_WARNING);
trigger_error("Error example", E_USER_ERROR);
?>

This code triggers three different PHP error levels: notice, warning, and fatal error.

Execution Table

Step	Action	Error Triggered?	Error Type	Error Level	Effect
1	Run trigger_error with E_USER_NOTICE	Yes	User Notice	E_USER_NOTICE	Notice message shown, script continues
2	Run trigger_error with E_USER_WARNING	Yes	User Warning	E_USER_WARNING	Warning message shown, script continues
3	Run trigger_error with E_USER_ERROR	Yes	User Error	E_USER_ERROR	Fatal error message shown, script stops
4	Script tries to continue after fatal error	No	-	-	Script stops, no further execution

💡 Script stops after fatal error (E_USER_ERROR) because it is a critical error level.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
error_triggered	false	true (notice)	true (warning)	true (fatal error)	script stopped
script_status	running	running	running	stopped	stopped

Key Moments - 3 Insights

Why does the script stop after the third error but not after the first two?

Because E_USER_ERROR is a fatal error level that stops script execution, unlike E_USER_NOTICE and E_USER_WARNING which only show messages but allow the script to continue (see execution_table rows 1-3).

Are notices and warnings errors that break the program?

No, notices and warnings inform about issues but do not stop the program. Only fatal errors stop execution (see execution_table rows 1 and 2).

What happens if an error level is not handled?

PHP uses default behavior: notices and warnings show messages, fatal errors stop the script. Custom handlers can change this (not shown here).

Visual Quiz - 3 Questions

Look at the execution table, what error level causes the script to stop?

A E_USER_NOTICE

B E_USER_ERROR

C E_USER_WARNING

D No error stops the script

💡 Hint

Check the Effect column in execution_table row 3 where the script stops.

At which step does the script still continue running after an error?

A Steps 1 and 2

B Step 1 only

C Step 3 only

D No steps, script stops immediately

💡 Hint

Look at script_status in variable_tracker after Step 1 and Step 2.

If the third trigger_error used E_USER_WARNING instead of E_USER_ERROR, what would happen?

A Script would stop immediately at step 1

B Script would stop at step 3

C Script would continue after step 3

D No error messages would show

💡 Hint

Refer to the Effect column for E_USER_WARNING in execution_table rows 2 and 3.

Concept Snapshot

PHP errors have types and levels:
- Notice (E_USER_NOTICE): minor, script continues
- Warning (E_USER_WARNING): important, script continues
- Fatal Error (E_USER_ERROR): critical, script stops
Use trigger_error() to create errors.
Script stops only on fatal errors.

Full Transcript

PHP runs code and checks for errors. Errors have types like Notice, Warning, and Fatal Error. Notices and Warnings show messages but let the script keep running. Fatal Errors stop the script immediately. The example code triggers one of each error type. The execution table shows the script continues after Notice and Warning but stops after Fatal Error. Variables track if an error happened and if the script is running. Beginners often wonder why some errors stop the script and others don't. The key is the error level. This helps understand how PHP handles problems during execution.