Exception Handling in PHP

Royce Roy 2218 10-Jun-2016

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

Royce Roy

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