Warning: array_filter() expects at Most 2 Parameters, 3 Given

Question

I have the following code that was taken from example #3 in the PHP documentation for the function array_filter():

$arr = array('a' => 1, 'b' => 2, 'c' => 3, 'd' => 4);

var_dump(array_filter($arr, function($k) {
    return $k == 'b';
}, ARRAY_FILTER_USE_KEY));

Interestingly, when testing this code to answer in this question, I got the following error:

Warning:
array_filter() expects at Most 2 Parameters, 3 Given in /path/to/file.php on line X

See on the Ideone.

But in the documentation, the function is described as capable of accepting 3 parameters:

array array_filter ( array $array [, callable $callback [, int $flag = 0 ]] )

The third parameter is exactly why you were using this function to solve the problem.

Question

What’s happening so I can’t make use of the three parameters?

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^{Version of PHP: 5.3.22 | Host: Linux | Server API: CGI/Fastcgi}

Answer 1

Of documentation of function array_filter:

5.6.0 Added optional flag Parameter and constants ARRAY_FILTER_USE_KEY and ARRAY_FILTER_USE_BOTH

Your PHP version does not support the third argument from flag.