function sanitize($data)
{
	$data = trim($data); 
	if(get_magic_quotes_gpc())
	{
		$data = stripslashes($data);
	}
	$data = mysql_real_escape_string($data);
	return $data;
}

//example
$username = sanitize($_POST['username']);

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The function returns the "sanitized" version of user input. Use before putting variables into SQL code.

Sanitize user input PHP

mysql, php, function

PHP