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up vote 3 down vote favorite

Following code:

<?php
$test_array = array();
$test_array['string_index'] = "data in string index";
$test_array[] = "data in index 0";
$test_array[] = "data in index 1";
$test_array[] = "data in index 2";

foreach($test_array as $key => $val)
{
    if($key != 'string_index')
    {
        echo $val."<br>";
    }
}
?>

gives result:

data in index 1
data in index 2

Question is - where is "data in index 0"??? How to get elements from numeric indices 0-n? Also if I change 'string_index' to something else which doesn't exist, it echoes everything except [0]. Plz, explain me this.

Thnx in advance

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4 Answers

up vote 11 down vote accepted

That's because the 'index 0' data has key 0. In PHP, 0 (number zero), '0' (string zero), and '' (empty string) are all equivalent - they can get typecast to each other. If you'd simply done print_r($test_array), you'd get 

Array
(
    [string_index] => data in string index
    [0] => data in index 0
    [1] => data in index 1
    [2] => data in index 2
)

The other option would have been to use the strict inequality test (!==) which compares value AND type. In that case, 0 !== 'string index' evaluates to true and everything works as expected.

Comment followup:

if you'd change the inside of your loop to this:

echo "key: $key (", gettype($key), ") val: $val (", gettype($val), ")\n";
if($key != 'string_index') {
    echo "$key != 'string_index'\n";
} else {
    echo "$key == 'string_index'\n";
}

You'll get:

key: string_index (string) val: data in string index (string)
string_index == 'string_index'
key: 0 (integer) val: data in index 0 (string)
0 == 'string_index'
key: 1 (integer) val: data in index 1 (string)
1 != 'string_index'
key: 2 (integer) val: data in index 2 (string)
2 != 'string_index'

As you can see, they're all there - it's your comparison that was failing you, because you didn't take PHP's typecasting/conversion rules into account.

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3  
0 != 'string index' evaluates to true too, surely. There is no test against the empty string. –  Lightness Races in Orbit Feb 26 '11 at 15:18
    
but 0 should be != 'string index'? i mean, there is no sane way php can typecast them to be the same, can it? –  knittl Feb 26 '11 at 15:22
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up vote 3 down vote

Had me puzzled for a second too :) You just need to make it !== not !=

<?php
$test_array = array();
$test_array['string_index'] = "data in string index";
$test_array[0] = "data in index 0";
$test_array[] = "data in index 1";
$test_array[] = "data in index 2";

foreach($test_array as $key => $val)
{
    if($key !== 'string_index')
    {
        echo $val."<br>";
    }
}
?>

That fixes your issue.

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up vote 1 down vote

Use === or !== instead of ==, != respectively, you need to validate type cast with some strict comparison operators.

 <?php
     $test_array = array();
     $test_array['string_index'] = "data in string index";
     $test_array[] = "data in index 0";
     $test_array[] = "data in index 1";
     $test_array[] = "data in index 2";

     foreach($test_array as $key => $val)
     {
        if($key ==='string_index')
        {
           //do something
        }else{
           echo $key.$val."<br>";
        }
     }
 ?>
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up vote 0 down vote

To clarify:
The reason that 0 != 'string_index' is that the string is apparently "downcast" to an integer in a string / integer comparison, and string_index is parsed until a character is encountered that is not a digit, thereby evaluating to the empty string which equals 0.

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