As a warning, do not use this function alone for input validation. 
Vulnerable example:
<?php
if(isset($_GET['id']) && intval($_GET['id']) > 0){
 echo $id;
}
?>

The following requests would pass this filter:
/page.php?id=10
/page.php?id=10oops
/page.php?id=10<script>alert(1)</script>
/page.php?id=1' OR '1'='1
/page.php?id[]=<script>alert(1)</script>
Instead use the is_numeric() function for integer validation:
<?php
echo intval("10oops"); // 10
echo is_numeric("10oops"); // false
?>

Secure example:
<?php
if(isset($_GET['id']) && is_numeric($_GET['id']) && intval($_GET['id']) > 0){
 echo $id;
}
?>