我正在尝试学习 PHP，但我一直遇到 PHP 错误。这是网站http://projects.jeremyohmann.com/homework的链接。有人可以查看我的代码以了解我做错了什么吗？我认为错误出现在 head.php 中，但也可能出现在 Login.php 中。用户在页面刷新后不断退出，所以我假设它与 php 会话有关。
我得到的确切错误是：
Warning: session_start() [function.session-start]: Cannot send session cookie - headers already sent by (output started at /home/jeremyohmann/www/projects/homework/head.php:2) in /home/jeremyohmann/www/projects/homework/classes/Login.php on line 30
Warning: session_start() [function.session-start]: Cannot send session cache limiter - headers already sent (output started at /home/jeremyohmann/www/projects/homework/head.php:2) in /home/jeremyohmann/www/projects/homework/classes/Login.php on line 30
头文件
<html>
<?php
require_once ('config/config.php');
require_once ('config/db.php');
require_once ('classes/Login.php');
$login = new Login(); ?>
<head>
<title>Homework Managment Project</title>
<link rel="stylesheet" type="text/css" href="reset.css">
<link rel="stylesheet" type="text/css" href="style.css">
</head>
<div id="wrapper">
<div id="header"><h1>Homework Management Project</h1></div>
<div id="nav">
<ul id="nav">
<li><a href="index.php">Home</a></li>
<li><a href="register.php">Register</a></li>
<li><a href="about.php">About</a></li>
<li><a href="classes.php">Classes</a></li>
<?php
//ask is user is logged in.
if($login->isUserLoggedIn()==true){
//show this if the user is logged in.
include('views/show-username.php');}
else{
//show this if the user isn't logged in.
include('views/nav-login-form.php');}
?>
</ul>
</div>
<div id="content">
登录.php
<?php
/**
* class Login
* handles the user login/logout/session
*
* @author Panique <panique@web.de>
* @version 1.2
*/
class Login {
private $db_connection = null; // database connection
private $user_name = ""; // user's name
private $user_email = ""; // user's email
private $user_password_hash = ""; // user's hashed and salted password
private $user_is_logged_in = false; // status of login
public $errors = array(); // collection of error messages
public $messages = array(); // collection of success / neutral messages
/**
* the function "__construct()" automatically starts whenever an object of this class is created,
* you know, when you do "$login = new Login();"
*/
public function __construct() {
// create/read session
session_start();
// check the possible login actions:
// 1. logout (happen when user clicks logout button)
// 2. login via session data (happens each time user opens a page on your php project AFTER he has sucessfully logged in via the login form)
// 3. login via post data, which means simply logging in via the login form. after the user has submit his login/password successfully, his
// logged-in-status is written into his session data on the server. this is the typical behaviour of common login scripts.
// if user tried to log out
if (isset($_GET["logout"])) {
$this->doLogout();
}
// if user has an active session on the server
elseif (!empty($_SESSION['user_name']) && ($_SESSION['user_logged_in'] == 1)) {
$this->loginWithSessionData();
// if user just submitted a login form
} elseif (isset($_POST["login"])) {
$this->loginWithPostData();
}
}
private function loginWithSessionData() {
// set logged in status to true, because we just checked for this:
// !empty($_SESSION['user_name']) && ($_SESSION['user_logged_in'] == 1)
// when we called this method (in the constructor)
$this->user_is_logged_in = true;
}
private function loginWithPostData() {
// if POST data (from login form) contain non-empty user_name and non-empty user_password
if (!empty($_POST['user_name']) && !empty($_POST['user_password'])) {
// create a database connection, using the constants from config/db.php (which we loaded in index.php)
$this->db_connection = new mysqli(DB_HOST, DB_USER, DB_PASS, DB_NAME);
// if no connection errors (= working database connection)
if (!$this->db_connection->connect_errno) {
// escape the POST stuff
$this->user_name = $this->db_connection->real_escape_string($_POST['user_name']);
// database query, getting all the info of the selected user
$checklogin = $this->db_connection->query("SELECT user_id,user_name, user_email, user_password_hash, first_name, last_name FROM users WHERE user_name = '".$this->user_name."';");
// if this user exists
if ($checklogin->num_rows == 1) {
// get result row (as an object)
$result_row = $checklogin->fetch_object();
// using PHP's crypt function to
// this is currently (afaik) the best way to check passwords in login processes with PHP/SQL
if (crypt($_POST['user_password'], $result_row->user_password_hash) == $result_row->user_password_hash) {
// write user data into PHP SESSION [a file on your server]
$_SESSION['user_id'] = $result_row->user_id;
$_SESSION['user_name'] = $result_row->user_name;
$_SESSION['user_email'] = $result_row->user_email;
$_SESSION['first_name'] = $result_row->first_name;
$_SESSION['last_name'] = $result_row->last_name;
$_SESSION['user_logged_in'] = 1;
// set the login status to true
$this->user_is_logged_in = true;
} else {
$this->errors[] = "Wrong password. Try again.";
}
} else {
$this->errors[] = "This user does not exist.";
}
} else {
$this->errors[] = "Database connection problem.";
}
} elseif (empty($_POST['user_name'])) {
$this->errors[] = "Username field was empty.";
} elseif (empty($_POST['user_password'])) {
$this->errors[] = "Password field was empty.";
}
}
/**
* perform the logout
*/
public function doLogout() {
$_SESSION = array();
session_destroy();
$this->user_is_logged_in = false;
$this->messages[] = "You have been logged out.";
}
/**
* simply return the current state of the user's login
* @return boolean user's login status
*/
public function isUserLoggedIn() {
return $this->user_is_logged_in;
}
}
索引.php
<?php include('head.php') ?>
<p>This is the test site for the Homework Grade Checker... Please check back soon to see if more progress has been made.</p>
<?php include('foot.php') ?>