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PHP Throwing Exceptions
Introduction
Throwable interface is implemented by Error and Exception class. All predefined Error classes are inherited from Error class. Instance of corresponding Error class is thrown inside try block and processed inside appropriate catch block.
Throwing Error
Normal execution (when no exception is thrown within the try block) will continue after that last catch block defined in sequence.
Example
<?php
function div($x, $y) {
if (!$y) {
throw new Exception('Division by zero.');
}
return $x/$y;
}
try {
echo div(10,5) . "
";
echo div(10,0) . "
";
} catch (Exception $e) {
echo 'Caught exception: ', $e->getMessage(), "
";
}
// Continue execution
echo "Execution continues
";
?>Output
Following output is displayed
2 Caught exception: Division by zero. Execution continues
In following example, TypeError is thrown while executing a function because appropriate arguments are not passed to it. Corresponding error message is displayed
Example
<?php
function add(int $num1, int $num2){
return $num1 + $num2;
}
try {
$value = add(1, 'one');
} catch (TypeError $e) {
echo $e->getMessage(). "
";
}
?>Output
Following output is displayed
Argument 2 passed to add() must be of the type integer, string given
SPL Exceptions
Standard PHP library contains predefined exceptions
| LogicException | Exception that represents error in the program logic. |
| BadFunctionCallException | Exception thrown if a callback refers to an undefined function or if some arguments are missing. |
| BadMethodCallException | Exception thrown if a callback refers to an undefined method or if some arguments are missing. |
| DomainException | Exception thrown if a value does not adhere to a defined valid data domain. |
| InvalidArgumentException | Exception thrown if an argument is not of the expected type. |
| LengthException | Exception thrown if a length is invalid. |
| OutOfRangeException | Exception thrown when an illegal index was requested. |
| RuntimeException | Exception thrown if an error which can only be found on runtime occurs. |
| OutOfBoundsException | Exception thrown if a value is not a valid key. |
| OverflowException | Exception thrown when adding an element to a full container. |
| RangeException | Exception thrown to indicate range errors during program execution. An arithmetic error other than under/overflow. |
| UnderflowException | Exception thrown when performing an invalid operation on an empty container, such as removing an element. |
| UnexpectedValueException | Exception thrown if a value does not match with a set of values. |
Following example shows OutOfBoundsException thrown when a key in PHP array is not found
Example
<?php
$arr=array("one"=>1, "two"=>2,"three"=>3,"four"=>4);
$key="ten";
try{
if (array_key_exists($key, $arr)==FALSE){
throw new OutOfBoundsException("key not found");}
else {
echo $arr[$key];}
}
catch (OutOfBoundsException $e){
echo $e->getMessage(). "
";
}
?>Output
Following output is displayed
key not found
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