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Bug #52426 switch() does not issue PHP Notice for uninitialized variable
Submitted: 2010-07-24 08:21 UTC Modified: 2010-09-20 14:59 UTC
From: gphemsley at gmail dot com Assigned:
Status: Not a bug Package: Scripting Engine problem
PHP Version: 5.2.14 OS:
Private report: No CVE-ID: None
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 [2010-07-24 08:21 UTC] gphemsley at gmail dot com 
Description:
------------
If the parameter passed to switch() is an uninitialized variable, a PHP Notice documenting such is not issued.

Test script:
---------------
<?php

error_reporting( E_ALL );

var_dump( PHP_VERSION, $mode );

switch( $mode )
{
    default:
        print '<p>There should be 2 notices of "undefined variable: mode".<br />' . "\n";
        print 'One for the var_dump() and one for the switch().</p>' . "\n";
    break;
}

highlight_file( $_SERVER['SCRIPT_FILENAME'] );

?> 

Expected result:
----------------
In the above script, two notices of "Undefined variable: mode" should be issued, one for the var_dump() and one for the switch().

Actual result:
--------------
In reality, only one notice is issued: the one for the var_dump(). (Taking out that call means that no notices are issued.)

I've gotten confirmation that this is present in 5.2.4, 5.2.5, and 5.3.2.

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 [2010-08-18 12:17 UTC] brendel at krumedia dot de 
If you add some cases to the switch the notice it triggered.
 [2010-09-20 14:37 UTC] iliaa@php.net
-Status: Open +Status: Bogus
 [2010-09-20 14:37 UTC] iliaa@php.net 
Thank you for taking the time to write to us, but this is not
a bug. Please double-check the documentation available at
http://www.php.net/manual/ and the instructions on how to report
a bug at http://bugs.php.net/how-to-report.php

Unless you have "case:" statements inside the switch the condition of the switch 
never actually gets used, because it does not get used it means no notices are 
being raised.
 [2010-09-20 14:59 UTC] gphemsley at gmail dot com 
That seems counter-intuitive to me, to just ignore code like that. (Obviously, if I write "switch", I intend there to be a switch.)

I assume the portion of the documentation you're referring to (in your canned message) is this:
"In the beginning, no code is executed. Only when a case statement is found with a value that matches the value of the switch expression does PHP begin to execute the statements."

The context of those statements appears to be referring to the code within the switch, as is inherent in the use of a switch: If you don't hit a case that is true, then you don't execute the code in that case block. It says nothing about the contents of the switch() call itself.

If you insist that this is desired behavior (a claim which I disagree with), I'd at least recommend that the documentation be updated to make this clear.
 
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