在PHP中，会话变量不存储该值。哪里不对？

Question

以下是一个示例PHP代码。我希望会话变量't'在更新函数被调用时递增其值。但是，当我运行代码时，我始终将输出作为值：1.我应该怎么做才能将值存储到会话变量中？

<?php 
session_start();  
if(!isset($_SESSION['t'])) { 
    $_SESSION['t'] = 0; 
} 
?> 
<div id="test" class="test"></div> 

<script src="http://code.jquery.com/jquery.js"></script> 

<script> 
    function update() { 

     var ct = "<?php echo $_SESSION['t'] += 1 ?>"; 

     <?php echo "Value: " . $_SESSION['t']; ?>; 

     $("#test").html(ct); 
    } 

    $(document).ready(function() { 
     setInterval('update()', 1000); 
    }); 
</script> 

Answer 1

把session_start()在脚本的最顶端，任何输出

<?php 
    session_start(); 

    // if you automatically set SESSION['t'] to 0 when the page loads, it will never increment 
    // check if the SESSION exists, and if it doesn't, then we create it 
    if(!isset($_SESSION['t'])) { 
     $_SESSION['t'] = 0; 
    } 
?> 


<div id="test" class="test"></div> 

<!-- it's recommended to load scripts at the end of the page --> 
<script src="http://code.jquery.com/jquery.js"></script> 

<script> 
    function update() { 
     // you had some formatting issues in here... 

     // shortcut: using +=1 will take the current value of $_SESSION['t'] and add 1 
     var ct = "<?php echo $_SESSION['t'] += 1 ?>"; 

     <?php echo "Value: " . $_SESSION['t']; ?>; 

     $("#test").html(ct); 
    } 

    $(document).ready(function() { 
     setInterval('update()', 1000); 
    }); 
</script> 

更新前： 这是一个例子，将做你要找我想什么。当页面加载时，它将显示$_SESSION['t']的值，然后在每次单击更新按钮时递增$_SESSION['t']的值。没有错误检查，这只是一个非常简单的例子，向你展示这是如何工作的。

<?php 
    session_start(); 

    if(!isset($_SESSION['t'])) { 
     $_SESSION['t'] = 0; 
    } 
?> 


<div id="test" class="test"></div> 

<button type="button" id="update">Update</button> 


<script src="http://code.jquery.com/jquery.js"></script> 

<script> 
    $(document).ready(function() { 

     // create the ct varaible 
     var ct = <?php echo $_SESSION['t']; ?>; 

     // display the value in the #test div 
     $("#test").text(ct); 

     // when the update button is clicked, we call ajax.php 
     $("#update").click(function(){ 
      $.post("ajax.php", function(response){ 

       // display the returned value from ajax.php 
       $("#test").text(response); 
      }); 
     }); 

    }); 
</script> 

ajax.php

<?php 

session_start(); 

// increment the session by 1 
$_SESSION['t'] += 1; 

// return the result 
echo $_SESSION['t'];