我有三个页面：
- index.php
- login.php和
- logout.php
如果您没有登录，索引页会将您重定向到登录页。当您登录时，它会将您重新定向到索引页，您可以在那里注销。一切都很顺利。但这很奇怪，在我看来不应该。
据我所知。Header、setcookie和会话语句只能在将任何输出发送到浏览器，但如果您查看login.php页面，它已经发送了HTML代码。为什么不起作用？我在这里错过了什么？
index.php:
<?php
if (isset ($_COOKIE['uid'])) {
?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Index Page</title>
</head>
<body>
Logged in with UID: <?php echo $_COOKIE['uid']; ?>
<br/>
<a href="logout.php">Log Out</a>
</body>
</html>
<?php
} else {
/* If no UID is in the cookie, we redirect to the login page */
header('Location: http://localhost/cookie/login.php');
}
?>
login.php：
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Login</title>
</head>
<body>
<?php
function check_auth() {
return 4;
}
if (isset ($_POST['login']) && ($uid = check_auth($_POST['email'], $_POST['password'])))
{
/* User succesfully logged in, setting cookie */
setcookie('uid', $uid, time() + 14400, '/');
header('Location: http://localhost/cookie/index.php');
} elseif (isset($_COOKIE['uid'])) {
/* If try to go to login.php when you already logged in, we redirect to the index page */
header ('Location: http://localhost/cookie/index.php');
} else {
?>
<h1>Log-in</h1>
<form method="post" action="login.php">
<table>
<tr><td>E-mail address:</td><td><input type='text' name='email'/></td></tr>
<tr><td>Password:</td><td><input type='password' name='password'/></td></tr>
<tr><td colspan='2'><input type='submit' name='login' value='Log in'/></td></tr>
</table>
</form>
<?php
}
?>
</body>
</html>
logout.php：
<?php
setcookie('uid', '', time() - 86400, '/');
header('Location: http://localhost/cookie/login.php');
?>
login.php文件中的header（）函数确实很奇怪。标头应该已经发送，并且不应该工作。你为什么不试试
bool headers_sent ([ string &$file [, int &$line ]] )
查看标头是否已发送？
http://www.php.net/manual/en/function.headers-sent.php