直接访问也不提示错误，自动跳转到 yes.php了求大神呀login.php 文件
<?php
session_start();
if($_POST["sub"] && !null){
$username=$_POST["username"];
$_SESSION["username"]=$username;
}
header("Location:yes.php");?>
<html>
<head><title>login</title></head>
<body>
<form action="login.php" method="POST">
<input type="text" name="username">
<input type="submit" name="sub">
</body>
</html>yes.php 文件
<?php
session_start();
echo $_SESSION["username"];
session_destroy();
?>
<?php
session_start();
if($_POST["sub"] && !null){
$username=$_POST["username"];
$_SESSION["username"]=$username;
}
header("Location:yes.php");?>
<html>
<head><title>login</title></head>
<body>
<form action="login.php" method="POST">
<input type="text" name="username">
<input type="submit" name="sub">
</body>
</html>yes.php 文件
<?php
session_start();
echo $_SESSION["username"];
session_destroy();
?>
if($_POST["sub"] && !null){ //这个!null何用？
$username=$_POST["username"];
$_SESSION["username"]=$username; //$_SESSION["username"]=$_POST["username"];
}
header("Location:yes.php");
你这个header应该放在if里面，不然始终会跳转