数组和会话-'var'和$ var之间的区别

Question

I'm trying to understand PHP array right now. What's the different between

$_SESSION['var'] and $_SESSION[$var]?

And how and when can we access variable like this - $_SESSION[$var][1]?

Thanks! :D

Answer 1

If you use $var as an array index, the value of $var will be used as the index:

$var = "foo";

$_SESSION['foo'] = "bar";
$_SESSION['var'] = "variable";

echo $_SESSION['var']; // This will echo "variable"
echo $_SESSION[$var];  // This will echo "bar"

As for your second example, in $_SESSION[$var][1] the string contained in $_SESSION[$var] will be accessed as an array of letters, returning the character in index 1 - the second letter.

Answer 2

In the former, 'var' is the "key" of the $_SESSION array. In the latter, the variable $var holds a value which is the "key" of the $_SESSION array.

Answer 3

With $_SESSION['var'] you specify the value with the key var ; with $_SESSION[$var] you specify the value with the key with the value of $var :

$arr = array('var' => 1, 'foo' => 2);
$var = 'foo';
var_dump($arr['var']);  // int(1)
var_dump($arr[$var]);   // int(2)

And before the question arises: $arr["$var"] is equivalent to $arr[$var] (here $var is converted to string internally). And although $arr[var] is handled equivalently as $var['var'] , you shouldn't use the former. See also Array dos and don'ts .

Answer 4

$var is an variable 'var' is an string. If you say

$_SESSION['my_string'] = 1;

this would be the same as

$anything = 'my_string';
$_SESSION[$anything] = 1;

because $anything is 'my_string'. In this example:

$_SESSION['test'] = 'test output';
$demo = 'demo';
$_SESSION[$demo] = 'demo output';

echo $_SESSION['test']; // outputs "test output"

echo $_SESSION['demo']; // outputs "demo output" and is the same as:
echo $_SESSION[$demo]; // outputs "demo output".

you can see how it works.

Answer 5

on the second question, there is no problem accessing them, just like you said:

$_SESSION[$first][$second].

on the first answer, see Kaivosukeltaja, he has given a great answer