Exception handling is a powerful mechanism in PHP, which is used to handle runtime errors (runtime errors are called exceptions).
The main purpose of using exception handling is to maintain the normal execution of the application.
Exception
An exception is an unexpected outcome of a program, which can be handled by the program itself.
Basically, an exception disrupts the normal flow of the program.
But it is different from an error because an exception can be handled, whereas an error cannot be handled by the program itself.
Need for Exception Handlers
Exception handling is required when an exception interrupts the normal execution of the program or application.
PHP provides a powerful mechanism for exception handling.
It can be used to handle runtime errors such as IOException, SQLException, ClassNotFoundException, and more.
A most popular example of exception handling is the divide by zero exception, which is an arithmetic exception.
Try block
The try block contains the code that may have an exception or where an exception can arise.
When an exception occurs inside the try block during runtime of code, it is caught and resolved in catch block.
The try block must be followed by a catch or finally block.
A try block can be followed by minimum one and any number of catch blocks.
Catch block
The catch block contains the code that executes when a specified exception is thrown.
It is always used with a try block, not alone.
When an exception occurs, PHP finds the matching catch block.
Throw block
t is a keyword used to throw an exception.
It also helps to list all the exceptions that a function throws but does not handle itself.
Remember that each throw must have at least one "catch".
Finally block
The finally block contains code, which is used for clean-up activity in PHP.
Basically, it executes the essential code of the program.
Exception outcome
The current state of the code is saved.
The execution of the code is switched to a predefined exception handler function.
Depending on the situation,
- the handler can halt the execution of the program,
- resume the execution from the saved code state,
- or continue the execution of the code from another location in the code.
//Script using Exception Handler
<?php
//user-defined function with an exception
function checkNumber($num) {
if($num>=1) {
//throw an exception
throw new Exception("Value must be less than 1");
}
return true;
}
//trigger an exception in a "try" block
try {
checkNumber(5);
//If the exception throws, the below text will not be displayed
echo 'If you see this text, the passed value is less than 1';
}
//catch exception
catch (Exception $e) {
echo 'Exception Message: ' .$e->getMessage();
}
?>