PHP Development | Tutorial 4 | PHP Error Handling & Debugging

by christopher | Sep 26, 2025 | PHP Development, Web App Development | 0 comments

Every developer encounters errors—syntax mistakes, undefined variables, failed database connections. For beginners in PHP, PHP error handling & debugging are essential skills. Poorly handled errors can crash applications or expose sensitive information to users. On the other hand, structured error handling improves user experience, system stability, and security.

In interviews, questions around PHP error handling often test your knowledge of exception handling, error reporting levels, and debugging tools. Let’s break it down.

Types of Errors in PHP

PHP errors can be broadly classified into:

1. Parse Errors (Syntax Errors) – Caused by typos or missing characters.

echo "Hello World" // Missing semicolon causes a parse error

2. Fatal Errors – When PHP cannot continue execution.
Example: calling an undefined function.

3. Warning Errors – Non-fatal; execution continues.

include("non_existing_file.php"); // Warning, script continues

4. Notice Errors – Minor errors like using an undefined variable.

Error Reporting in PHP

PHP allows developers to control what errors are displayed:

<?php
error_reporting(E_ALL);  // Report all errors
ini_set('display_errors', 1);  // Show errors on screen

👉 In production, never display errors directly to users. Instead, log them:

ini_set('log_errors', 1);
ini_set('error_log', '/var/log/php_errors.log');

Exception Handling in PHP

PHP introduced exceptions for structured error handling.

Basic Example:

<?php
function divide($a, $b) {
    if ($b == 0) {
        throw new Exception("Division by zero is not allowed");
    }
    return $a / $b;
}

try {
    echo divide(10, 0);
} catch (Exception $e) {
    echo "Error: " . $e->getMessage();
}

👉 Output:
Error: Division by zero is not allowed

Custom Exception Classes

class InvalidAgeException extends Exception {}

function registerUser($age) {
    if ($age < 18) {
        throw new InvalidAgeException("User must be 18 or older");
    }
    return "User registered successfully";
}

try {
    echo registerUser(15);
} catch (InvalidAgeException $e) {
    echo "Registration Failed: " . $e->getMessage();
}

👉 Creating custom exceptions makes your codebase more descriptive and easier to maintain.

Debugging Techniques in PHP

Debugging is about finding the root cause of errors quickly.

1. Using var_dump and print_r

$user = ["name" => "Karthick", "role" => "Admin"];
var_dump($user);

2. Using Xdebug

Xdebug is a PHP extension that provides:

Step debugging.
Stack traces.
Profiling.
Code coverage.

3. Logging

Always log errors in production instead of displaying them.

4. dd() and dump() in Laravel

Laravel developers use dd() (die and dump) for quick debugging

$user = User::find(1);
dd($user);

Common Mistakes Beginners Make

Displaying errors directly in production (security risk).
Using @ (error suppression operator) excessively.
Not differentiating between warnings and fatal errors.
Failing to use try-catch around database queries or file operations.

Sample Interview Questions & Answers

Q: What’s the difference between error and exception in PHP?

A: An error is a system-level issue (syntax, memory). Exceptions are program-level events that can be caught and handled.

Q: What does error_reporting(E_ALL) do?

A: It tells PHP to report all errors, warnings, and notices.

Q: Why should you avoid displaying errors in production?

A: Exposed errors may reveal sensitive paths, SQL queries, or server details, leading to security vulnerabilities.

Q: What is the use of finally block in PHP exception handling?

A: The finally block always executes, regardless of whether an exception occurred, useful for cleanup (like closing DB connections).

Q: How can you debug PHP applications efficiently?

A: Use tools like Xdebug, logging, and Laravel’s dd() function for quick inspection.

Q: How does Laravel handle errors differently from vanilla PHP?

A: Laravel uses a centralized error handler (App\Exceptions\Handler) and integrates with logging tools like Monolog.

Closing Note

PHP Error Handling & Debugging are critical for building secure, stable, and professional applications. As you progress into frameworks like Laravel, you’ll find structured error handling, logging, and debugging tools that make life easier.