$_POST and php

Hey, how can I loop through the _POST super-global array and get the field name? I know how to get the field value, but i need the field name. For example:

<input type='hidden' name='FVid_type' value='int' />

I need to my PHP program to output "FVid_type", not "int"

PHP Code:

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foreach ($_POST as $key=>$value) {
   echo $key;
} 


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$key is the current key and $value is the current value of the array $_POST.

Thanks a bunch, you've really helped