PHP json_encode as object after PHP array unset()

I’m experiencing odd behavior with json_encode after removing a numeric array key with unset. The following code should make the problem clear. I’ve run it from both the CLI and as an Apache mod:

PHP version info:

C:\Users\usr\Desktop>php -v
PHP 5.3.1 (cli) (built: Nov 20 2009 17:26:32)
Copyright (c) 1997-2009 The PHP Group
Zend Engine v2.3.0, Copyright (c) 1998-2009 Zend Technologies

PHP Code


$a = array(
    new stdclass,
    new stdclass,
    new stdclass
$a[2]->nmo = '567';

printf("%s\n", json_encode($a));
printf("%s\n", json_encode($a));

Program Output

C:\Users\usr\Desktop>php test.php

As you can see, the first time $a is converted to JSON it’s encoded as a javascript array. The second time around (after the unset call) $a is encoded as a javascript object. Why is this and how can I prevent it?

The reason for that is that your array has a hole in it: it has the indices 0 and 2, but misses 1. JSON can’t encode arrays with holes because the array syntax has no support for indices.

You can encode array_values($a) instead, which will return a reindexed array.

In addition to the array_values technique it is possible to use array_splice and remove an element and re-index in one step:



array_splice($a, 1, 1);

Try to use JSON_FORCE_OBJECT option for json_encode, like: json_encode($a, JSON_FORCE_OBJECT) so you will always have the same result.

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