传递$ _POST到array_key_exists（）时的PHP警告

So I am using the following style of code if(array_key_exists('some_value', $_POST)){echo 'hi';}

For PHP 5.2.17 I am getting a warning from this style of code. This is the warning: WARNING: argument 2 for array_key_exists() is not either an array or an object on line: 123

This seems strange to me because I believe that the $_POST array should always be defined. Is that not the case? I'm not sure what would cause the $_POST array to not be considered an array. I am not resetting $_POST to anything so it should exist as an array at all times. Does anyone have any idea what is wrong. Please let me know if more information is needed and thank you for the help.

Edit: I should note that this only happens on the production server. My local environment does not have this problem.

The Superglobals $_POST and $_GET are only populated if the script is POSTed to or GET from. In your example, the reason that you'd get that error is if there was not post action to the script. Before checking for a certain post value, you should check to make sure there was a post:

if(isset($_POST)) {
    //The form was posted
}

In that fashion. From there, you can check for certain values using array_key_exist, or you can further check isset($_POST['myKey']).

Use if(isset($_POST['some_value'])) { echo 'hi'; } instead. Never had a problem with it.

Also check if you are not overriding or unsetting $_POST (or some framework you are using is doing it for you). I avoid to do so with superglobal variables since I think it is a bad practice and might give headaches like this one.