wp: Limit Post Content by Amount of Characters

functions.php

<?php
function short_content($num) {
$limit = $num+1;
$content = str_split(get_the_content());
$length = count($content);
if ($length>=$num) {
$content = array_slice( $content, 0, $num);
$content = implode("",$content)."...";
echo '<p>'.$content.'</p>';
} else {
the_content();
}
}
?>

// Usage <?php short_content(20);?>