Check if key exists in $_SESSION by building index string - php

Question

I need to check if a key exists and return its value if it does.
Key can be an array with subkeys or endkey with a value.
$_SESSION['mainKey']['testkey'] = 'value';
var_dump(doesKeyExist('testkey'));
function doesKeyExist($where) {
$parts = explode('/',$where);
$str = '';
for($i = 0,$len = count($parts);$i<$len;$i++) {
$str .= '[\''. $parts[$i] .'\']';
}
$keycheck = '$_SESSION[\'mainKey\']' . $str;
if (isset(${$keycheck})) {
return ${$keycheck};
}
// isset($keycheck) = true, as its non-empty. actual content is not checked
// isset(${$keycheck}) = false, but should be true. ${$var} forces a evaluate content
// isset($_SESSION['mainKey']['testkey']) = true
}
Using PHP 5.3.3.

Answer 1

Instead of building the string, just check if the key exists within your loop.
For instance:
function doesKeyExist($where) {
$parts = explode('/',$where);
$currentPart = $_SESSION['mainKey'];
foreach($parts as $part) {
if (!isset($currentPart[$part])) {
return false;
}
$currentPart = $currentPart[$part];
}
return true;
}

Answer 2

function getByKeys($keys, $array) {
$value = $array;
foreach (explode('/', $keys) as $key) {
if (isset($value[$key])) {
$value = $value[$key];
} else {
return null;
}
}
return $value;
}

Answer 3

Perhaps I'm misunderstanding the question, but this would appear to be the simplest way of doing it:
function getKey($arr, $key) {
if (array_key_exists($key, $arr)) {
return $arr[$key];
} else {
return false;
}
}
$value = getKey($_SESSION['mainKey'], 'testkey');

Answer 4

You should use $$keycheck, not ${$keycheck}.
The last notation is only if you use the variable inside a string (e.g. "${$keycheck}")
See http://php.net/manual/en/language.variables.variable.php for more details about variable variables

Answer 5

You might want to use the eval() php function for this.
function doesKeyExist($where) {
$parts = explode('/',$where);
$str = '';
for($i = 0,$len = count($parts);$i<$len;$i++) {
$str .= '["'. $parts[$i] .'"]';
}
eval('$keycheck = $_SESSION["mainKey"]' . $str . ';');
if (isset($keycheck)) {
return $keycheck;
}
}
HTH