PHP exception handling method in code debugging _php tutorial

An exception (Exception) is used to change the normal process of a script when a specified error occurs.

What is an exception?

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

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

When an exception is triggered, it usually occurs:

Current code state is saved
Code execution is switched to the pre-defined exception handler function
Depending on the situation, the processor may start executing the code again from the saved code state, terminating the script execution, or continuing the script from another location in the code
We will show you different error handling methods:

Basic use of exceptions
Creating a custom exception handler
Multiple exceptions
To re-throw an exception
Setting the top-level exception handler
Basic use of exceptions
When the exception is thrown, the subsequent code does not continue, and PHP tries to find a matching "catch" block.

If the exception is not captured and does not use Set_exception_handler () for appropriate processing, a serious error (fatal error) will occur, and an error message "Uncaught exception" (uncaught exception) is output.

Let's try to throw 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 is 1 or below in C:webfolderest.php:6 Stack trace: #0 C: webfolderest.php (Mon): Checknum #1 {main} thrown in c:webfolderest.php on line 6
Try, throw, and catch
To avoid the error in the above example, we need to create the appropriate code to handle the exception.

The processing handler should include:

Try-the function that uses the exception should be in the "try" code block. If no exception is triggered, the code will continue to execute as usual. However, if an exception is triggered, an exception is thrown.
Throw-this specifies how the exception is triggered. Each "throw" must correspond to at least one "catch"
Catch-the "catch" code block catches an exception and creates an object that contains the exception information
Let's trigger an exception:

1) {throw new Exception ("Value must be 1 or below");} return true; }//triggers an exception in the "try" code block try {checknum (2);//if the exception is thrown, this text won't is shown echo If Number is 1 or below; }//catch Exception catch (Exception $e) {echo Message:. $e->getmessage ();}? >
The above code will get an error like this:

Message:value must be 1 or below
Example Explanation:
The above code throws an exception and captures it:

Create the Checknum () function. It detects if the number is greater than 1. If it is, an exception is thrown.
Call the Checknum () function in the "Try" code block.
The exception in the Checknum () function is thrown
The catch code block receives the exception and creates an object ($e) that contains the exception information.
Output the error message from this exception by calling $e->getmessage () from this exception object
However, to follow the principle that each throw must correspond to a catch, you can set up a top-level exception handler to handle the missing error.
To create a custom Exception class
Creating a custom exception handler is straightforward. We have simply created a special class that can call its function when an exception occurs in PHP. The class must be an extension of the exception class.

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

We started to create the exception class:

Class Customexception extends Exception {
Public Function errormessage () {
Error message
$ERRORMSG = Error on line. $this->getline (). In. $this->getfile ().: $this->getmessage (). was 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. Because it is a copy of the old class, it inherits properties and methods from the old class, and we can use the methods of the exception class, such as GetLine (), GetFile (), and GetMessage ().

Example Explanation:
The above code throws an exception and captures it through a custom exception class:

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

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

!--? php
class customexception extends Exception{public function errormessage () {
//error
message$ ErrorMsg = Error on line. $this->getline (). In. $this->getfile ().: . $this->getmessage (). was 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 I S an example e-mail "); }}catch (Customexception $e) {echo $e->errormessage ();} catch (Exception $e) {echo $e->getmessage ();}?
Example Explanation:
The code above tests two conditions, and throws an exception if any condition is not true:

The Customexception () class is created as an extension of the old exception class. So it inherits all the properties and methods of the old class.
Create the ErrorMessage () function. If the e-mail address is not valid, the function returns an error message.
Executes a "try" block of code that, under the first condition, does not throw an exception.
Because e-mail contains the string "Example", the second condition triggers an exception.
Catch code block catches exceptions and displays appropriate error messages
If the customexception is not captured and the base exception is tightly captured, the exception is handled there.
To re-throw an exception
Sometimes, when an exception is thrown, you might want to handle it in a different way from the standard. You can throw an exception again in a "catch" code block.

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

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 if the message address contains the string "example". If there is, throw the exception again:

The Customexception () class is created as an extension of the old exception class. So it inherits all the properties and methods of the old class.
Create the ErrorMessage () function. If the e-mail address is not valid, the function returns an error message.
Set the $email variable to a valid e-mail address, but with the string "

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