attempting to assign a property to an array

Question

I have an array called $my_array . I created $my_array like this:

 $my_array = [];
 $my_array[0] = [];
 $my_array[1] = [];
 $my_array[2] = [];
 $my_array[3] = [];

Each element of $my_array is an array:

foreach ($my_array as $array){
    print(gettype($array));
    print(" ///   ");
}

output: array /// array /// array /// array ///

foreach ($my_array as $array){


    $array['link_root'] = "a string";

    print($array['link_root']);
    print("     /////     ");
}

output is: a string ///// a string ///// a string ///// a string /////

and then when I try:

print($my_array[0]['link_root'])

I get: PHP error: Undefined index: link_root

How do I iteratively set a value for a key/property of an array and why is this not working?

Try a `print_r()` or a `var_dump()` first to see whats in array `$my_array`.. Secondly, the array you're trying to write to while looping is a copy. — Xorifelse, Nov 16 '16 at 21:54

Jeremy Harris · Accepted Answer · 2016-11-16T22:00:42.660

3

The foreach control structure does not pass the value by reference by default.

If you want to be able modify the array internally, you need to use & to indicate you want it passed as a reference like so:

foreach ($myArray as &$array) {
    $array['link_root'] = "a string";
}

print($myArray[0]['link_root']);

The difference is subtle. Another way to do this is pass the index and reference it directly like:

foreach ($myArray as $index => $array) {
    $myArray[$index]['link_root'] = "a string";
}

print($myArray[0]['link_root']);

edited Nov 16 '16 at 22:00

answered Nov 16 '16 at 21:57

Jeremy Harris

I believe there where some implications using the refference method, I can't recall what they where though. – Xorifelse Nov 16 '16 at 21:58
1

@Xorifelse Probably about unsetting the variable after the loop to avoid modifying the main array by accident when you re-use the loop variable later on. – jeroen Nov 16 '16 at 22:00
1

@jeroen I found it, you need to [unset](http://stackoverflow.com/a/5810200/4982088) after foreach otherwise it can cause undesired behavior. – Xorifelse Nov 16 '16 at 22:03
Good point! Thanks for pointing that out, I had forgotten that. – Jeremy Harris Nov 16 '16 at 22:03
@Xorifelse Exactly :-) – jeroen Nov 16 '16 at 22:04

1 Answers1