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Date: Thu, 15 Jul 2010 21:42:46 -0400
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Subject: Unintuitive array_combine() behaviour
From: joel.perras@gmail.com (Joel Perras)

array_combine(array(), array()) triggers an E_WARNING and returns
false, instead of simply returning an empty array with no triggered
warning.

This is not a bug, but was intentionally written as such - see
ext/standard/array.c around lines 4480-4483 in the 5.3 branch in the
current svn HEAD:


PHP_FUNCTION(array_combine)
{
	zval *values, *keys;
	HashPosition pos_values, pos_keys;
	zval **entry_keys, **entry_values;
	int num_keys, num_values;

	if (zend_parse_parameters(ZEND_NUM_ARGS() TSRMLS_CC, "aa", &keys,
&values) =3D=3D FAILURE) {
		return;
	}

	num_keys =3D zend_hash_num_elements(Z_ARRVAL_P(keys));
	num_values =3D zend_hash_num_elements(Z_ARRVAL_P(values));

	if (num_keys !=3D num_values) {
		php_error_docref(NULL TSRMLS_CC, E_WARNING, "Both parameters should
have an equal number of elements");
		RETURN_FALSE;
	}

	if (!num_keys) {
		php_error_docref(NULL TSRMLS_CC, E_WARNING, "Both parameters should
have at least 1 element");
		RETURN_FALSE;
	}

// [snip]


There is currently one open ticket regarding this behaviour
(http://bugs.php.net/bug.php?id=3D34857) from 2005, as well as a ticket
that was closed, stating that the incorrect E_WARNING message was
fixed (http://bugs.php.net/bug.php?id=3D29972). This behaviour is also
documented on http://php.net/array_combine .

So, it's easy to see that this has been around for a while. However, I
don't think this behaviour is intuitive or very logical. Am I missing
something obvious?

Thanks,
Jo=C3=ABl.

P.S.
I've searched back to about 2004 in the php-internals list to see if
this topic has come up before, but came up empty. If this has already
been discussed ad nauseam, could someone please link me to the
relevant posts?

--=20
I do know everything, just not all at once. It's a virtual memory problem.