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Error and Exception Handling

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Error and exception handling is a crucial aspect of PHP programming. It helps in identifying, managing, and resolving errors that occur during the execution of a script. This module will cover the basics of error handling, different types of errors, and how to use exceptions to manage errors effectively.

Key Concepts

  1. Types of Errors in PHP

    • Parse Errors: Syntax errors that occur during the parsing of the script.
    • Fatal Errors: Critical errors that halt the execution of the script.
    • Warning Errors: Non-critical errors that allow the script to continue running.
    • Notice Errors: Minor errors that do not affect the script execution.

  2. Error Reporting

    • Configuring error reporting levels.
    • Using error_reporting() function.

  3. Handling Errors

    • Using die() and exit() functions.
    • Custom error handling with set_error_handler().

  4. Exception Handling

    • Understanding exceptions.
    • Using try, catch, and finally blocks.
    • Creating custom exceptions.

Error Reporting

Configuring Error Reporting Levels

PHP provides a way to control which errors are reported using the error_reporting() function. You can set different levels of error reporting based on your needs.

<?php
// Report all errors
error_reporting(E_ALL);

// Report all errors except E_NOTICE
error_reporting(E_ALL & ~E_NOTICE);

// Turn off error reporting
error_reporting(0);
?>

Practical Example

<?php
// Turn on error reporting for all errors
error_reporting(E_ALL);

// This will cause a notice error
echo $undefined_variable;

// This will cause a warning error
include('non_existent_file.php');

// This will cause a fatal error
non_existent_function();
?>

Handling Errors

Using die() and exit()

The die() and exit() functions can be used to terminate the script execution when an error occurs.

<?php
$file = 'somefile.txt';

if (!file_exists($file)) {
    die("File not found");
}

// Continue with the script if the file exists
echo "File found";
?>

Custom Error Handling

You can create a custom error handler using the set_error_handler() function.

<?php
function customErrorHandler($errno, $errstr, $errfile, $errline) {
    echo "Error: [$errno] $errstr - $errfile:$errline";
    // You can log the error or take other actions here
}

// Set the custom error handler
set_error_handler("customErrorHandler");

// Trigger an error
echo $undefined_variable;
?>

Exception Handling

Understanding Exceptions

Exceptions provide a way to handle errors gracefully. They allow you to catch and manage errors without stopping the script execution.

Using try, catch, and finally Blocks

<?php
function divide($dividend, $divisor) {
    if ($divisor == 0) {
        throw new Exception("Division by zero");
    }
    return $dividend / $divisor;
}

try {
    echo divide(10, 0);
} catch (Exception $e) {
    echo "Caught exception: " . $e->getMessage();
} finally {
    echo "This block is always executed";
}
?>

Creating Custom Exceptions

You can create your own exception classes by extending the Exception class.

<?php
class CustomException extends Exception {
    public function errorMessage() {
        return "Error on line " . $this->getLine() . " in " . $this->getFile() . ": " . $this->getMessage();
    }
}

try {
    throw new CustomException("A custom error has occurred");
} catch (CustomException $e) {
    echo $e->errorMessage();
}
?>

Practical Exercises

Exercise 1: Custom Error Handler

Create a custom error handler that logs errors to a file.

<?php
function logErrorHandler($errno, $errstr, $errfile, $errline) {
    $log = "Error: [$errno] $errstr - $errfile:$errline\n";
    file_put_contents('error_log.txt', $log, FILE_APPEND);
}

// Set the custom error handler
set_error_handler("logErrorHandler");

// Trigger an error
echo $undefined_variable;
?>

Exercise 2: Exception Handling

Write a function that reads a file and throws an exception if the file does not exist.

<?php
function readFileContent($filename) {
    if (!file_exists($filename)) {
        throw new Exception("File not found");
    }
    return file_get_contents($filename);
}

try {
    echo readFileContent('non_existent_file.txt');
} catch (Exception $e) {
    echo "Caught exception: " . $e->getMessage();
}
?>

Summary

In this module, you learned about different types of errors in PHP, how to configure error reporting, and how to handle errors using built-in functions and custom error handlers. You also explored exception handling using try, catch, and finally blocks, and learned how to create custom exceptions. These techniques are essential for writing robust and maintainable PHP code.

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PHP Programming Course

Module 1: Introduction to PHP

Module 2: Control Structures

Module 3: Functions

Module 4: Arrays

Module 5: Working with Forms

Module 6: Working with Files

Module 7: Object-Oriented Programming (OOP)

Module 8: Working with Databases

Module 9: Advanced PHP Techniques

Module 10: PHP Frameworks and Best Practices

Module 11: Project: Building a Web Application

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