Weird behavior of matching array keys after json_decode()

I've got some very weird behavior in my PHP code. I don't know if this is actually a good SO question, since it almost looks like a bug in PHP. I had this problem in a project of mine and isolated the problem:

// json object that will be converted into an array
$json = '{"5":"88"}';
$jsonvar = (array) json_decode($json); // notice: Casting to an array
// Displaying the array:
var_dump($jsonvar);
// Testing if the key is there
var_dump(isset($jsonvar["5"]));
var_dump(isset($jsonvar[5]));

That code outputs the following:

array(1) {
  ["5"]=>
  string(2) "88"
}
bool(false)
bool(false)

The big problem: Both of those tests should produce bool(true) - if you create the same array using regular p开发者_JAVA技巧hp arrays, this is what you'll see:

// Let's create a similar PHP array in a regular manner:
$phparr = array("5" => "88");
// Displaying the array:
var_dump($phparr);
// Testing if the key is there
var_dump(isset($phparr["5"]));
var_dump(isset($phparr[5]));

The output of that:

array(1) {
  [5]=>
  string(2) "88"
}
bool(true)
bool(true)

So this doesn't really make sense. I've tested this on two different installations of PHP/apache.

You can copy-paste the code to a php file yourself to test it.

It must have something to do with the casting from an object to an array.

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Use the json_decode function parameters to get an array, instead of changing an object yourself.

json_decode ( string $json [, bool $assoc = false])
$assoc - When TRUE, returned object s will be converted into associative array s.

Your code, when changed to

$jsonvar = json_decode($json, true);

works as expected

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It can be further simplified to this problem

$o = new stdClass;
$o->{5} = 1; //or even $o->{'5'} = 1;
$a = (array) $o;
print_r($a); // Array([5] => 1)
var_dump(isset($a[5])); // false
var_dump(isset($a['5'])); // false

It seems that this only happens when the property name is one that php would normally consider a numeric key in an array.

Definitely unexpected behavior to me.

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edit Same issue here Casting an Array with Numeric Keys as an Object

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edit#2 documented behavior http://www.php.net/manual/en/language.types.array.php#language.types.array.casting

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As chris said, you are hitting one of the limits of the json <-> object <-> array mappings.

Another interesting one to keep in mind is when a key in a json object is the empty string.

json = '{"":"88"}';

the key will be mapped to php as "empty" !

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Use a statement like

$value = $a["'".$i."'"];

directly following the line that goes

$a = json_decode($a, true);