What is the difference between error constants and exception constants in PHP?

Answer: Error constants are error conditions when PHP is running, while exception constants are user-defined exception types. Difference comparison: Value: error constants are predefined integers, and exception constants are user-defined class constants. Source: Error constants come from the PHP runtime, exception constants come from user code. Reporting method: Error constants are reported through the error_reporting() function, and exception constants are reported through try-catch blocks. Severity: Error constants range from fatal errors to warnings, and the severity of exception constants is determined by the developer. Recoverability: Error constants are not recoverable, exception constants can be handled through try-catch blocks.

The difference between error constants and exception constants in PHP

In PHP, there are significant differences in the uses and behaviors of error constants and exception constants . This article will delve into these differences and illustrate them with real-life examples.

Error constants

Error constants represent error conditions that occur when PHP is running. They are predefined integers, starting with E_. For example:

• E_ERROR: Serious error and cannot be recovered.
• E_WARNING: Runtime error, recoverable.
• E_NOTICE: Warning that does not affect code execution.

In PHP, use the error_reporting() function to control which error constants are reported.

Exception constants

Exception constants represent the types of exceptions thrown in PHP code. They are different from error constants, which are user-defined. By using the class keyword, you can customize exception classes and define exception constants. For example:

class MyException extends Exception {
    const MY_ERROR = 1234;
}

In code, you can use the following method to throw an exception:

throw new MyException('...', MyException::MY_ERROR);

Difference comparison table

##ValuesPredefined integersUser-defined class constantsSourcePHP runtimeUser code Reporting method##SeverityRecoverabilitytry-catch

Features	Error constants	Exception constants
	error_reporting() Function	try-catch Block
From fatal error to warning	Up to developer discretion
Unrecoverable	Recoverable (Can be processed through	block)

Actual case

The following is a usage error constant and a practical example of exception constants:

<?php

// 设置错误报告级别，报告所有错误
error_reporting(E_ALL);

try {
    // 抛出自定义异常
    throw new MyException('错误描述', MyException::MY_ERROR);
} catch (Exception $e) {
    // 处理异常
    echo "错误代码：" . $e->getCode();
    echo "<br>";
    echo "错误信息：" . $e->getMessage();
}

In this example, the

error_reporting()

function is used to report all errors, including fatal errors and warnings. try-catch block is used to handle user-defined exceptions. When MyException is thrown, its code and message will be printed to the screen.

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