php防止sql注入原理介绍

if (!get_magic_quotes_gpc()) {

　　$lastname = addslashes($_POST[‘lastname’]);

　　} else {

　　$lastname = $_POST[‘lastname’];

}

$sql = "select count(*) as ctr from users where username02.='".mysql_real_escape_string($username)."' and 03.password='". mysql_real_escape_string($pw)."' limit 1";

function inject_check($sql_str) {
    return eregi('select|insert|and|or|update|delete|'|/*|*|../|./|union|into|load_file|outfile', $sql_str);
}
 
function verify_id($id=null) {
    if(!$id) {
        exit('没有提交参数！');
    } elseif(inject_check($id)) {
        exit('提交的参数非法！');
    } elseif(!is_numeric($id)) {
        exit('提交的参数非法！');
    }
    $id = intval($id);
    
    return $id;
}
 
 
function str_check( $str ) {
    if(!get_magic_quotes_gpc()) {
        $str = addslashes($str); // 进行过滤
    }
    $str = str_replace("_", "_", $str);
    $str = str_replace("%", "%", $str);
    
   return $str;
}
 
 
function post_check($post) {
    if(!get_magic_quotes_gpc()) {
        $post = addslashes($post);
    }
    $post = str_replace("_", "_", $post);
    $post = str_replace("%", "%", $post);
    $post = nl2br($post);
    $post = htmlspecialchars($post);
    
    return $post;
}