PHP function code for security filtering of input information_PHP tutorial

// define constannts for input reading
define('INPUT_GET', 0x0101);
define('INPUT_POST', 0x0102);
define('INPUT_GPC', 0x0103);

/**
* Read input value and convert it for internal use
* Performs stripslashes() and charset conversion if necessary
*
* @param string Field name to read
* @param int Source to get value from (GPC)
* @param boolean Allow HTML tags in field value
* @param string Charset to convert into
* @return string Field value or NULL if not available
*/
function get_input_value($fname, $source, $allow_html=FALSE, $charset=NULL) {
$value = NULL;

if ($source == INPUT_GET && isset($_GET[$fname]))
$value = $_GET[$fname];
else if ($source == INPUT_POST && isset($_POST[$fname]))
$value = $_POST[$fname];
else if ($source == INPUT_GPC) {
if (isset($_POST[$fname]))
$value = $_POST[$fname];
else if (isset($_GET[$fname]))
$value = $_GET[$fname];
else if (isset($_COOKIE[$fname]))
$value = $_COOKIE[$fname];
}

if (empty($value))
return $value;

// strip single quotes if magic_quotes_sybase is enabled
if (ini_get('magic_quotes_sybase'))
$value = str_replace("''", "'", $value);
// strip slashes if magic_quotes enabled
else if (get_magic_quotes_gpc() || get_magic_quotes_runtime())
$value = stripslashes($value);

// remove HTML tags if not allowed
if (!$allow_html)
$value = strip_tags($value);

// convert to internal charset
return $value;
}