PHP json_encode as object after PHP array unset()

Question

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

<?php  $a = array(     new stdclass,     new stdclass,     new stdclass ); $a[0]->abc = '123'; $a[1]->jkl = '234'; $a[2]->nmo = '567';  printf("%s\n", json_encode($a)); unset($a[1]); printf("%s\n", json_encode($a)); 

Program Output

C:\Users\usr\Desktop>php test.php [{"abc":"123"},{"jkl":"234"},{"nmo":"567"}] {"0":{"abc":"123"},"2":{"nmo":"567"}} 

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?

Answer 1

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

unset($a[1]); 

Instead:

array_splice($a, 1, 1); 

Answer 2

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.