• PHP 5 is that you can now use exceptions, like other OOP languages.


• PHP 5 introduces an exceptions objects to simplify your error .


• An Exception is any unusual condition that causes an alteration in program flow, such as a missing file or a null pointer.


• There are different error handling methods:


• Basic use of Exceptions.
• Creating a custom exception handler.
• Multiple exceptions.
• Re-throwing an exception Setting a top level exception handler.

Use of Exceptions :

• When an exception is thrown,so that code will not be executed, and will try to find the matching "catch" block.


• If an exception is not caught, a fatal error will be issued with an "Uncaught Exception" message.

Example :

<?php
//create function with an exception
function check($num)
  {
  if($num>10)
    {
    throw new Exception("Value must be 10 or below");
    }
  return true;
  }
//trigger exception
check(11);
?>

Output :

Fatal error: Uncaught exception 'Exception' with message 'Value must be 10 or below' in C:\xampp\htdocs\First\exception.php:7 Stack trace: #0>
C:\xampp\htdocs\First\exception.php(13):check(11) #1 {main} thrown

Try, throw and catch

• Try :try is used to define a block of code in which exception can be occurred.


• Catch :catch block immediately after try block. The catch block will tell your program just what to do in case the exception actually does occur. If no exception occurs, then the catch block is ignored, and your program moves along smoothly.


• Throw :to throw an exception explicitly.

Example :

<?php
//create function with an exception
function check($num)
{
	if($num>10)
	{
		throw new Exception("Value must be 10 or below");
	}
	return true;
}

// exception in a "try" block
try
{
	check(10);
	//If the exception is thrown,
	echo 'If you see this, the number is 10 or below';
}

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

Output :

If you see this, the number is 10 or below 

Creating a Custom Exception Class

• We can create own exceptions by extending 'Exception' class.


• Own exception is also known as "User Defined Exception".

Example :

<?php
class customException extends Exception
  {
  public function errorDisplay()
    {
    //error message
    $errorMsg = 'Error on line '.$this->getLine().' in '.$this->getFile()
    .': <b>'.$this->getMessage().'</b> is invalid E-Mail address';
    return $errorMsg;
    }
  }

$email = "abc@example..com";

try
  {
  //check if
  if(filter_var($email, FILTER_VALIDATE_EMAIL) === FALSE)
    {
    //throw exception if email is invalid
    throw new customException($email);
    }
  }

catch (customException $e)
  {
  //display custom message
  echo $e->errorDisplay();
  }
?>

Output :

Error on line 21 in C:\xampp\htdocs\First\customException.php: abc@example..com is invalid E-Mail address 
	

Multiple Catch

• A single try block can have multiple catch blocks.


• It's required when the try block has statements that generates different types of exceptions.


• If the first catch block contains the Exception class object then the subsequent catch blocks are never executed.


• The last catch block in multiple catch blocks must contain the Exception class object.


• Because the java complier gives an error saying that the subsequent catch blocks haven't been reached.

Example :

<?php
class customException extends Exception
{
public function errorDisplay()
{
//error message
$errorMsg = 'Error on line '.$this->getLine().' in '.$this->getFile()
.': '.$this->getMessage().' is not a valid E-Mail address';
return $errorMsg;
}
}

$email = "abc@example.com";

try
  {
  //check if
  if(filter_var($email, FILTER_VALIDATE_EMAIL) === FALSE)
    {
    //throw exception if email is invalid
    throw new customException($email);
    }
  //check for "example" in mail address
  if(strpos($email, "example") !== FALSE)
    {
    throw new Exception("$email is e-mail");
    }
  }

catch (customException $e)
  {
  echo $e->errorDisplay();
  }

catch(Exception $e)
  {
  echo $e->getMessage();
  }
?>

Output :

abc@example.com is e-mail

Re-throwing Exceptions

• If you use throw an exception more than one time within a "catch" block.

Example :

<?php
class customException extends Exception
  {
  public function errorDisplay()
    {
    //error dispkay
    $errorMsg = $this->getMessage().' is invalid E-Mail address.';
    return $errorMsg;
    }
  }

$email = "abc@example.com";

try
  {
  try
    {
    //check for "example" in mail address
    if(strpos($email, "example") !== FALSE)
      {
      //throw exception if email is invalid
      throw new Exception($email);
      }
    }
  catch(Exception $e)
    {
    //re-throw exception
    throw new customException($email);
    }
  }

catch (customException $e)
  {
  //display custom message
  echo $e->errorDisplay();
  }
?>

Output :

abc@example.com is invalid E-Mail address.