Odd behaviour in a switch statement

Question

I\'m writing code for a sortable table, where clicking the links in the header change the ORDER BY executed when generating a set of search results (the case where there the

Answer 1

It's because of the way php casts strings to ints. When you pass in a 0, you are asking it to do an integer comparison, so it will convert all of your case keys to integers. When php casts a string to an int, it looks for an actual number at the beginning of the string, and gobbles the number up until it hits a non-number. Since the string "resnum" has no numbers, it returns 0. See here:

php > echo (int)"100";
100
php > echo (int)"300 dogs";
300
php > echo (int)"resnum";
0
php > echo (int)"resnum 100";
0

Since all of those strings cast to 0, the first case would evaluate to true since 0 == 0.

Resources:
String conversion to numbers
Type comparison tables

---

Nitpick time. When you're doing simple case statements that map a string to a string, use an array. It's much clearer and actually faster:

function sortMode ($name)
{
    $modeMap = array(
        'resnum'   => 'b_resnum',
        'state'    => 'st_id',
        'name'     => 'lastname, firstname',
        'phone'    => 'phone',
        'email'    => 'email',
        'opened'   => 'cs_created'
    );

    return isset($modeMap[$name]) ? $modeMap[$name] : '';
}

If the $name is set in the map, we return the value that key is mapped to. Otherwise, we return an empty string, which takes the place of the default case.

As a bonus, you would have noticed the bug earlier if you did the above method, because it would be trying to access $modeMap[0] and would have returned your default case instead.

Answer 2

The key point is that a switch() statement performs comparisons between the parameter and the labels. That means that you have to deal with PHP comparison and type casting rules. Just see some examples:

<?php

var_dump( ''==0 );    // bool(true)
var_dump( 'foo'==0 ); // bool(true)
var_dump( '0'==0 );   // bool(true)
var_dump( '0m'==0 );  // bool(true)
var_dump( '01'==0 );  // bool(false)

The reference can be found at:

• http://es.php.net/manual/en/language.operators.comparison.php
• http://es.php.net/manual/en/types.comparisons.php#types.comparisions-loose
• http://es.php.net/manual/en/control-structures.switch.php

Initializing an unset GET parameter to 0 is a pretty strange design decision. You should deal with that particular case in a separate fashion to make it clear that it's a special situation:

if( $name===0 ){
    return '';
}
switch($name){
    // ...
}