PHP：filter_var没有过滤[关闭]

Question

<?php

class validation {

function clean_txt($str, $letter_case="") {

    trim($str);
    filter_var($str, FILTER_SANITIZE_STRING);
    switch ($letter_case) {
        case "L":
            strtolower($str);
            break;
        case "U":
            strtoupper($str);
            break;
        case "T":
            ucwords($str);
            break;
        default:
            $str="";
    }
    return ($str);
}

function clean_email($email_var) {

    filter_var($email_var, FILTER_SANITIZE_EMAIL);
    return ($email_var);

}

function clean_int($int_var) {

    trim($int_var);
    filter_var($int_var, FILTER_SANITIZE_NUMBER_INT);
    return ($int_var);

}

$functions = new validation();
$var = $functions->clean_txt(" Hello, HOw Are you?", "L");
echo $var;
?>
<br>
<?php
$var = $functions->clean_email(":[e-mail]");
echo $var;
?>
<br>
<?php
$var = $functions->clean_int("38u");
echo $var;
?>

It returns:

Hello, HOw Are you?
:[e-mail]
38u

It SHOULD be returning:

hello, how are you?
[e-mail]
38

Does anyone see what I'm missing here? I know the methods are at least passing the variables through, and the trim() function is working just fine.

Answer 1

Functions like trim(), filter_var() and strtolower() don't modify the string itself, instead they return a copy. You need to store that return value in a variable:

function clean_txt($str, $letter_case="") {

    $str = trim($str);
    $str = filter_var($str, FILTER_SANITIZE_STRING);
    switch ($letter_case) {
        case "L":
            $str = strtolower($str);
            break;
        case "U":
            $str = strtoupper($str);
            break;
        case "T":
            $str = ucwords($str);
            break;
        default:
            $str="";
    }
    return ($str);
}

Similarly in clean_email() and clean_int().