Php if($_POST) vs if(isset($_POST))
<p>I have a simple form as demonstrated below:</p>

<pre><code>&lt;form action="" method="post"&gt;
  &lt;input type="text" /&gt;
  &lt;input type="submit" value="SEND" /&gt;
&lt;/form&gt;
</code></pre>

<p>When I try to receive data sent from this form via <code>if($_POST)</code>, I fail, but when try with <code>isset</code>, I success.</p>

<pre><code>if($_POST){
  echo 'a'; //Doesn't print anything.
}
if(isset($_POST)){
  echo 'b'; //Prints 'b'
}
</code></pre>

<p>I guess the reason behind it is missing name attribute in my form input, but I can't understand why <code>if($_POST)</code> and <code>isset($_POST)</code> react different ways in this case.</p>