Array key in php

Question

I'm trying to understand this code:

<?php 

$list = array(-10=>1, 2, 3, "first_name"=>"mike", 4, 5, 10=>-2.3); 

print_r(array_keys($list));
?>

Output:

Array ( [0] => -10 [1] => 0 [2] => 1 [3] => first_name [4] => 2 [5] => 3 [6] => 10 )

I'm wondering why [4] => 2 and why [5] => 3 i thought it would be [4] => 4 and [5] => 5 because they are both at index 4 and 5. I'm slightly confused as to what exactly is going on in this array, if possible could someone point me in the right direction, Thank You.

score 6 · Accepted Answer · answered May 02 '14 at 15:13

6

You're mixing keyed with keyless array entries, so it gets a bit wonky:

$list = array(
    -10 => 1   // key is -10
        => 2  // no key given, use first available key: 0
        => 3  // no key given, use next available key: 1
    "first_name" => "mike" // key provided, "first_name"
        => 4  // no key given, use next available: 2
        => 5  // again no key, next available: 3
     10 => -2.3  // key provided: use 10

If you don't provide a key, PHP will assign one, starting at 0. If the potential new key would conflict with one already assigned, that potential key will be skipped until PHP finds one that CAN be used.

answered May 02 '14 at 15:13

Marc B

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Thank You for the explanation, sadly this code was written by an examiner for my university past paper, so if its using wrong techniques thats pretty poor. – user3562135 May 02 '14 at 15:18
it's not really "wrong". but it does lead to headscratching if you don't know what's going on. My general rule is not do this kind of thing, ever, just because it can lead to confusion. – Marc B May 02 '14 at 15:31

score 1 · Answer 2 · answered May 02 '14 at 15:14

1

try this:

$list = array(-10=>1, 2 => null, 3=> null, "first_name"=>"mike", 4=> null, 5=> null, 10=>-2.3);

to have the result you want so 2, 3, 4 and 5 will be count as key instead of value

answered May 02 '14 at 15:14

ekans

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score 1 · Answer 3 · answered May 02 '14 at 15:15

1

It's normal because PHP is waiting for a key.

$list = array(-10=>1, 2, 3, "first_name"=>"mike", 4, 5, 10=>-2.3);

And you don't give him in 2,3,4,5 so it gives a key automatic .

So ==> [0] => 2 , [1] => 3 , [2] => 4 and [3] => 5.

answered May 02 '14 at 15:15

Dev'Hamz

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9

alexmngn · Answer 4 · 2014-05-02T15:18:03.503

0

In your array, you are mixing key => value with just value.

-10 is your first key. Then because you are not defining a key for following items, it's automatically assigned in order.

edited May 02 '14 at 15:18

answered May 02 '14 at 15:11

alexmngn

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array can have negative number keys – hindmost May 02 '14 at 15:14

score 0 · Answer 5 · answered May 02 '14 at 15:20

It seems like when the key is not set, array_keys keeps the track of the last key assigned and will assign the consecutive number:

array(7) {
  [0]=>
  int(-10)
  [1]=>
  int(0)   // first without key (starting on 0)
  [2]=>
  int(1)   // second without key
  [3]=>
  string(10) "first_name"
  [4]=>
  int(2)  // third without key 
  [5]=>
  int(3)  // fourth without key
  [6]=>
  int(10)
}

Array key in php

5 Answers5