PHP exception handling methods in code debugging_PHP tutorial

Exception is used to change the normal flow of the script when a specified error occurs.

What is an exception?

PHP 5 provides a new object-oriented approach to error handling.

Exception handling is used to change the normal flow of the script when a specified error (exception) situation occurs. This situation is called an exception.

When an exception is triggered, it usually happens:

Current code status is saved
Code execution is switched to the predefined exception handler function
Depending on the situation, the processor may restart code execution from a saved code state, terminate script execution, or continue script execution from another location in the code
We will show different error handling methods:

Basic use of exceptions
Create a custom exception handler
Multiple exceptions
Rethrow exception
Set top-level exception handler
Basic usage of exceptions
When an exception is thrown, the following code will not continue to execute, and PHP will try to find a matching "catch" block of code.

If the exception is not caught and there is no need to use set_exception_handler() for corresponding processing, then a serious error (fatal error) will occur and an "Uncaught Exception" error message will be output.

Let’s try throwing an exception without catching it:

//create function with an exceptionfunction
checkNum($number) {
if($number>1) {
throw new Exception("Value must be 1 or below");
} return true;
}
//trigger
exceptioncheckNum(2);
?>
The above code will get an error like this:

Fatal error: Uncaught exception Exception with message Value must be 1 or below in C:webfolder est.php:6 Stack trace: #0 C:webfolder est.php(12): checkNum(28) #1 {main} thrown in C:webfolder est.php on line 6
Try, throw and catch
To avoid the errors in the above example, we need to create appropriate code to handle exceptions.

Handling procedures should include:

Try - Functions that use exceptions should be inside a "try" block. If no exception is triggered, the code continues execution as usual. But if an exception is triggered, an exception will be thrown.
Throw - This specifies how to trigger the exception. Each "throw" must correspond to at least one "catch"
Catch - The "catch" code block will catch the exception and create an object containing the exception information
Let's trigger an exception:

1) { throw new Exception("Value must be 1 or below"); } return true; }//Trigger exception in "try" code block try { checkNum(2); //If the exception is thrown, this text will not be shown echo If you see this, the number is 1 or below; }//Capture Exception catch(Exception $e) { echo Message: .$e->getMessage(); }?>
The above code will get an error similar to this:

Message: Value must be 1 or below
Example explanation:
The above code throws an exception and catches it:

Create checkNum() function. It detects whether the number is greater than 1. If so, throw an exception.
Call the checkNum() function in the "try" block.
Exception in checkNum() function is thrown
The "catch" code block receives the exception and creates an object ($e) containing the exception information.
Output the error message from this exception by calling $e->getMessage() from this exception object
However, in order to follow the principle of "every throw must correspond to a catch", you can set up a top-level exception handler to handle missed errors.
Create a custom Exception class
Creating custom exception handlers is very simple. We simply created a specialized class whose functions are called when an exception occurs in PHP. This class must be an extension of the exception class.

This custom exception class inherits all the properties of PHP's exception class, and you can add custom functions to it.

We start creating the exception class:

class customException extends Exception {
public function errorMessage() {
//error message
$errorMsg = Error on line .$this->getLine(). in .$this->getFile() .: .$this->getMessage(). is not a valid E-Mail address; return $errorMsg;
}
}
$email = "someone@example...com";try {
//check if
if(filter_var($email, FILTER_VALIDATE_EMAIL) === FALSE) {
//throw exception if email is not valid throw
new customException($email);
}
}catch (customException $e)
{
//display custom message
echo $e->errorMessage();
}?>
This new class is a copy of the old exception class, plus the errorMessage() function. Just because it is a copy of the old class, it inherits the properties and methods from the old class, and we can use the methods of the exception class, such as getLine(), getFile(), and getMessage().

Explanation of examples:
The above code throws an exception and catches it through a custom exception class:

The customException() class was created as an extension of the old exception class. This way it inherits all properties and methods of the old class.
Create errorMessage() function. If the e-mail address is not valid, the function returns an error message
Set the $email variable to an illegal e-mail address string
Execute the "try" code block and throw an exception because the e-mail address is invalid
The "catch" code block catches the exception and displays the error message
Multiple exceptions
You can use multiple exceptions for a script to detect multiple situations.

You can use multiple if..else code blocks, or a switch code block, or nest multiple exceptions. These exceptions can use different exception classes and return different error messages:

class customException extends Exception{public function errorMessage(){
//error
message$errorMsg = Error on line .$this->getLine(). in .$this->getFile().: .$this->getMessage(). is not a valid E-Mail address;
return $errorMsg;
}
}
$email = "someone@example.com";try {
//check if
if(filter_var($email, FILTER_VALIDATE_EMAIL) === FALSE) {
//throw exception if email is not valid throw new
customException($email);
}
//check for "example" in mail address
if(strpos($email, "example") !== FALSE) { throw new Exception("$email is an example e-mail"); } }catch (customException $e) { echo $e->errorMessage( ); }catch(Exception $e) { echo $e->getMessage(); }?>
Example explanation:
The above code tests two conditions. If any condition is not true, an exception is thrown:

The customException() class was created as an extension of the old exception class. This way it inherits all properties and methods of the old class.
Create errorMessage() function. If the e-mail address is not valid, this function returns an error message.
Execute the "try" block of code, and in the first condition, no exception will be thrown.
Since the e-mail contains the string "example", the second condition triggers an exception.
The "catch" block will catch the exception and display the appropriate error message
If customException is not caught and the base exception is caught, the exception is handled there.
Rethrow exception
Sometimes, when an exception is thrown, you may want to handle it differently than the standard. The exception can be thrown again in a "catch" block.

The script should hide system errors from the user. System errors may be important to programmers, but users are not interested in them. To make it easier for users, you can throw the exception again with a user-friendly message:

//error message
$errorMsg = $this->getMessage(). is not a valid E-Mail address.; return $errorMsg; } }$email = "someone@example.com";try { try {
//check for "example" in mail address
if(strpos($email, "example") !== FALSE) {
//throw exception if email is not valid throw new
Exception($email); } } catch(Exception $e) {
//re-throw exception throw new
customException($email); } }catch (customException $e) {
//display custom message
echo $e->errorMessage(); }?>
Example explanation:
The above code detects whether the string "example" is contained in the email address. If so, throw the exception again:

The customException() class was created as an extension of the old exception class. This way it inherits all properties and methods of the old class.
Create errorMessage() function. If the e-mail address is not valid, this function returns an error message.
Set the $email variable to a valid email address, but containing the string "

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