为什么active user: <?php echo $_SESSION["username"];?>都不显示

Question

<?php
session_start();
if(isset($_SESSION['username'])){
?>
 active user: <?php echo $_SESSION["username"];?>
 <div class="form_row">
                    <a class="form1" href="logout.php">logout</a>
                   </div>
 <?php }else {?>
                    <form action="check.php" method="post" name="myform" onsubmit="return Checklogin(this);">          
                    <div class="form_row">
                    <label class="contact"><strong>username:</strong></label>
                    <input type="text" class="contact_input" name="username"/>
                    </div>  
                    <div class="form_row">
                    <label class="contact"><strong>Password:</strong></label>
                    <input type="password" class="contact_input" name="password"/>
                    </div>                                         <div class="form_row">
                        
                        
                       
                    </div>                     
                    <div class="form_row">
                    <input type="submit" class="register" value="login" name="login"/><a href="register.php">register</a>
                    </div>   
                    
               
                   <?php }?> 

Answer 1

如果代码没有问题，判断$_SESSION['username'] 是否真的存在

Answer 2

check.php
有没写入session啊？
检查一下

Answer 3

哦，check.php里忘记session_start();了