Exception Handling in PHP

Royce Roy 2767 10 Jun 2016 Updated 15 Mar 2018

Exceptions are important to control over error handling. Exception handlings are used to change the execution of a code if a specified error occurs.

Here are some keywords related to exception handling:

· Try: A function which is using an exception must be in a ‘try’ block. If the exception is triggered, an exception is thrown, otherwise if exception does not trigged, the code will continue its execution.

· Throw: This is how you trigger an exception. Each “throw” must have at least one catch.

· Catch- A catch block retrieves an exception and creates an object containing the information about exception.

<?php

// function is created with an exception
function check($num) {
  if($num>2) {
    throw new Exception("Value must be 2 or below");
  }
  return true;
}

// exception is triggered  in a "try" block
try {
  check (3);
  //If the exception is thrown, this text will not be shown
  echo ' the number is 2 or below';
}

//catch exception

catch(Exception $e) {
  echo 'Message: ' .$e->getMessage();
}

?>

Output:

Message: Value must be 1 or below

Example explained

· The check() function is created. It checks whether a number is greater than 2.If it is, than an exception is thrown.

· The check() function is called in a “try” block.

· The exception within check() function is thrown.

· After exception is thrown the catch block retrieves the exception and creates an object ($e) containing the information about exception.

· The error message is displayed by calling $e->getMessage() from the exception object.

Creating a custom Exception class in PHP

You can create your own custom exception handler. To create a custom exception handler you must create a special class function. This function is called when an exception occurs in PHP. The class must be an extension of the exception class. Use following function to set a user-defined exception handler function:

string set_exception_handler ( callback $exception_handler )

When uncaught exception occurs than exception_handler (the name of the function) is called.

<?php

   function exception_handler($error) {
      echo "An uncaught exception: " , $error->getMessage(), "\n";
   }
  set_exception_handler('exception_handler');
   throw new Exception('Uncaught Exception');
   echo “This is not Executed\n";

?>

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Exception Handling in PHP

Creating a custom Exception class in PHP

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