[SOLVED] Square Brackets after variable -- what does this do?

[danludwig]

Hi,

 

I don't have a PHP execution environment to test in, and am trying to read some PHP code to determine what it does. Say I declare a variable like so:

 

$var = array();

 

If I remember correctly, I can put values into this array like so:

$var["key1"] = "Some value";

$var[2] = "Some other value";

 

On the other hand, what does it mean if I do this?

$var[] = "Some third value";

 

Does this stack the value onto the end of the array? If so, does it not have a key, or does it use NULL as a key?

 

Also, in more strongly-typed languages, I'm used to managing keyed collections like this in objects like Hashtable (Java / CSharp / VB) rather than arrays. Hashtable in particular usually allows the use of NULL as a key once. Is it the same way in PHP? For example, if I have:

 

$key = null;

$array = array();

$array[$key] = "This is important information";

 

...how would I access the important information? By calling $array[null] on the right side of an expression?

 

Thanks,

 

Dan

[taquitosensei]

It adds to the array with the index being the next numerical value.

 

If you have this

$array[1]="blah";

this

$array[2]="whatever";

and

$array[]="whatever"; 

are the same thing

 

I don't think php allows null keys.  Numerically indexed arrays are generally accessed in a loop. If you need to access by a specific index. You would use an associative array.

$array['myname']="Mr. Coffee";

 

 

[mikesta707]

hmm, never tried to use a key as a null value before...

 

but yes $var[] will stack the value onto the end of the array. For numeric arrays, the key will just be the largest key +1. For an associative array, if you have no numbers as keys, the key will be zero. if you have a number, it will be the next increment.

 

for example, the following code:

<?php

$array = array("hi" => "too", "toad" => "pond", "goop" => "test", 0 => "ddd");
$array[] = "dd";

foreach($array as $key => $value){
echo $key . " => " . $value . "<br />";
}
?>

 

would output:

hi => too

toad => pond

goop => test

0 => ddd

1 => dd

 

(which I did verify on my test server)

 

and yes, you can use null as a key and call it via $array[null] (which I tested also)

 

hope that helps!

[ldougherty]

If you do not supply an index it will just add the item to the end of the array.

 

var[0] = 1;

var[1] = 2;

var[] = 3;

 

outputting the array would yield 1,2,3

[Maq]

To elaborate and clarify on ldougherty, the print_r() display would look like:

 

Array
(
    [0] => 1
    [1] => 2
    [2] => 3
)

 

(You also need to prefix the array with '$')

[danludwig]

Thanks everyone for the quick replies. I was confused because the code I'm looking at does in fact initialize a variable $key = null; then soon afterward assigns a value using $someArray[$key] = $someOtherVariable. I vaguely remembered from my PHP days that the brackets were a shortcut for adding to the end of an array, but wanted to make sure that this wasn't a shortcut to get the value stored under the NULL key.

 

To confirm, if I create an array like so:

 

$myArray = array();

$myArray["key1"] = "value1";

$myArray[] = "value2";

$myArray[1] = "value3";

$myArray[] = "value4";

 

... then the corresponding keys of the array, in order, are "key1", 0, 1, 2. Right?

 

I suppose my trick is going to be trying to figure out how to mimic a data structure like this in a more strongly-typed language. I was thinking Hashtable would work, but to add a value to one, you always have to specify a key. Guess I can just write a little helper method to auto-assign next int values and mimic an associative array.

 

Thanks again.

 

 

[mikesta707]

Thanks everyone for the quick replies. I was confused because the code I'm looking at does in fact initialize a variable $key = null; then soon afterward assigns a value using $someArray[$key] = $someOtherVariable. I vaguely remembered from my PHP days that the brackets were a shortcut for adding to the end of an array, but wanted to make sure that this wasn't a shortcut to get the value stored under the NULL key.

 

To confirm, if I create an array like so:

 

$myArray = array();

$myArray["key1"] = "value1";

$myArray[] = "value2";

$myArray[1] = "value3";

$myArray[] = "value4";

 

... then the corresponding keys of the array, in order, are "key1", 0, 1, 2. Right?

 

I suppose my trick is going to be trying to figure out how to mimic a data structure like this in a more strongly-typed language. I was thinking Hashtable would work, but to add a value to one, you always have to specify a key. Guess I can just write a little helper method to auto-assign next int values and mimic an associative array.

 

Thanks again.

 

 

 

Indeed they are. Just to test I ran the following script (basically yours with a foreach to output)

 

<?php

$myArray = array();
$myArray["key1"] = "value1";
$myArray[] = "value2";
$myArray[1] = "value3";
$myArray[] = "value4";

foreach($myArray as $key => $value){
echo $key . " => " . $value . "<br />";
}


?>

 

and the output was as follows:

 

key1 => value1

0 => value2

1 => value3

2 => value4

 

so again, yes you are correct

[danludwig]

Awesome, question solved/answered. Thanks again.