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异常处理

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PHP 5 has an exception model similar to that of other programming languages. An exception can be throw n, and caught (" catch ed") within PHP. Code may be surrounded in a try block, to facilitate the catching of potential exceptions. Each try must have at least one corresponding catch or finally block.

The thrown object must be an instance of the Exception class or a subclass of Exception. Trying to throw an object that is not will result in a PHP Fatal Error.

catch

Multiple catch blocks can be used to catch different classes of exceptions. Normal execution (when no exception is thrown within the try block) will continue after that last catch block defined in sequence. Exceptions can be throw n (or re-thrown) within a catch block.

When an exception is thrown, code following the statement will not be executed, and PHP will attempt to find the first matching catch block. If an exception is not caught, a PHP Fatal Error will be issued with an "Uncaught Exception ..." message, unless a handler has been defined with set_exception_handler() .

finally

In PHP 5.5 and later, a finally block may also be specified after or instead of catch blocks. Code within the finally block will always be executed after the try and catch blocks, regardless of whether an exception has been thrown, and before normal execution resumes.

注释

Note:

Internal PHP functions mainly use Error reporting, only modern Object oriented extensions use exceptions. However, errors can be simply translated to exceptions with ErrorException.

Tip

The Standard PHP Library (SPL) provides a good number of built-in exceptions.

范例

Example #3 Throwing an Exception

<?php
function  inverse ( $x ) {
    if (!
$x ) {
        throw new 
Exception ( 'Division by zero.' );
    }
    return 
1 / $x ;
}

try {
    echo 
inverse ( 5 ) .  "\n" ;
    echo 
inverse ( 0 ) .  "\n" ;
} catch (
Exception $e ) {
    echo 
'Caught exception: ' ,   $e -> getMessage (),  "\n" ;
}

// Continue execution
echo  "Hello World\n" ;
?>

以上例程会输出:

0.2
Caught exception: Division by zero.
Hello World

Example #4 Exception handling with a finally block

<?php
function  inverse ( $x ) {
    if (!
$x ) {
        throw new 
Exception ( 'Division by zero.' );
    }
    return 
1 / $x ;
}

try {
    echo 
inverse ( 5 ) .  "\n" ;
} catch (
Exception $e ) {
    echo 
'Caught exception: ' ,   $e -> getMessage (),  "\n" ;
finally  {
    echo 
"First finally.\n" ;
}

try {
    echo 
inverse ( 0 ) .  "\n" ;
} catch (
Exception $e ) {
    echo 
'Caught exception: ' ,   $e -> getMessage (),  "\n" ;
finally  {
    echo 
"Second finally.\n" ;
}

// Continue execution
echo  "Hello World\n" ;
?>

以上例程会输出:

0.2
First finally.
Caught exception: Division by zero.
Second finally.
Hello World

Example #5 Nested Exception

<?php

class  MyException  extends  Exception  { }

class 
Test  {
    public function 
testing () {
        try {
            try {
                throw new 
MyException ( 'foo!' );
            } catch (
MyException $e ) {
                
// rethrow it
                
throw  $e ;
            }
        } catch (
Exception $e ) {
            
var_dump ( $e -> getMessage ());
        }
    }
}

$foo  = new  Test ;
$foo -> testing ();

?>

以上例程会输出:

string(4) "foo!"