how to convert a string in array respect the spaces
<p>I have a string like this:</p>

<pre><code>$contenuto = "Lorem ipsum dolor sit amet, consectetur adipiscing elit. Ut lobortis condimentum commodo. Duis dui dui, rutrum et lacinia sit amet, lacinia in nulla.";
</code></pre>

<p>I need to break it into an array of substrings with a limit of 20 characters, like this:</p>

<pre><code>Array
(
    [0] =&gt; "Lorem ipsum dolor ";
    [1] =&gt; "sit amet, ";
    [2] =&gt; "consectetur ";
    [3] =&gt; "adipiscing elit. Ut ";
    [4] =&gt; "lobortis condimentum";
    [5] =&gt; "commodo. Duis dui ";
    [6] =&gt; "dui, rutrum et ";
    [7] =&gt; "lacinia sit amet, ";
    [8] =&gt; "lacinia in nulla.";
)
</code></pre>

<p>How can I do this?</p>
