Question

I’ve got a short question that I’ve been wondering about for a while. There is a perfect workaround, but I’d like to know what the problem really is.

I’ve got an array ($lines) consisting of underlying associative arrays. I want to get the indexes of one (basically any random one) of those underlying arrays, so I use:

$headers = array_keys($lines[0]);

However, this gives me back the following error:

Warning: array_keys() expects parameter 1 to be array, null given

But then, when I use this instead:

$line0 = $lines[0];
$headers = array_keys($line0);

Everything works exactly as I want it to. Now as far as I can see, these two should be perfectly equivalent, so I was wondering if this is a bug in PHP, or if I just fail to understand something here.

PHP version is 5.3.1

The $lines array looks like this in my test case:

Array (
    [0] => Array
        (
            [id] => 00
            [name] => John Doe
        )
    [1] => Array
        (
            [id] => 007
            [name] => James Bond
        )
)

Answer 1

I can’t reproduce.
I wrote the following file:

<?php

$lines = array(
    array("A" => 1, "B" => 2, "C" => 3),
    array("A" => 1, "B" => 2, "C" => 3),
    array("A" => 1, "B" => 2, "C" => 3)
);

echo "<pre>";
var_dump(array_keys($lines[0]));
echo "</pre>";

And it outputs correctly:

array(3) {
  [0]=>
  string(1) "A"
  [1]=>
  string(1) "B"
  [2]=>
  string(1) "C"
}

So I guess it’s either a bug in your program or in your php version but nothing “normal”.