sanitize user input php

1# sanitize form data
2function clean($data)
3{
4    $data = htmlspecialchars($data);
5    $data = stripslashes($data);
6    $data = trim($data);
7    return $data;
8}

1<?php
2function sanitize($stringToSanitize) {
3	return addslashes(htmlspecialchars($stringToSanitize));
4}
5// You can just use the codes themselves instead of creating a function as:
6echo addslashes(htmlspecialchars($stringToSanitize));
7?>

1<?php
2    function cleanUserInput($userinput) {
3  
4  		// Open your database connection
5      	$dbConnection = databaseConnect();
6  
7  		// check if input is empty
8        if (empty($userinput)) {
9          return;
10        } else {
11          
12        // Strip any html characters
13        $userinput = htmlspecialchars($userinput);
14        
15		// Clean input using the database  
16        $userinput = mysqli_real_escape_string($dbConnection, $userinput);
17        }
18       
19  	  // Return a cleaned string
20      return $userinput;
21    }
22?>