警告：不能更改頭信息，什麼是錯在我的代碼

Question

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什麼是錯在我的代碼，當每次我嘗試刪除一條記錄其給予警告信息.....請幫我

警告：不能更改頭信息 - 已經 發送頭（輸出開始在C：\ XAMPP \ htdocs中\ CMS \ ADMIN \ Categories.php：10） C：\ XAMPP \ htdocs中\ CMS \ ADMIN \在線181的Categories.php

<div id="wrapper"> 

    <!-- Navigation --> 

<?php include "includes/Navigation.php";?> 


     <!-- Top Menu Items --> 
     <ul class="nav navbar-right top-nav"> 
      <li><a href="../index.php"> Home Page </a></li> 

        <li class="dropdown"> 
       <a href="#" class="dropdown-toggle" data-toggle="dropdown"><i class="fa fa-user"></i> John Smith <b class="caret"></b></a> 
       <ul class="dropdown-menu"> 
        <li> 
         <a href="#"><i class="fa fa-fw fa-user"></i> Profile</a> 
        </li> 

        <li class="divider"></li> 
        <li> 
         <a href="#"><i class="fa fa-fw fa-power-off"></i> Log Out</a> 
        </li> 
       </ul> 
      </li> 
     </ul> 
     <!-- Sidebar Menu Items - These collapse to the responsive navigation menu on small screens --> 
     <div class="collapse navbar-collapse navbar-ex1-collapse"> 
      <ul class="nav navbar-nav side-nav"> 
       <li> 
        <a href="index.html"><i class="fa fa-fw fa-dashboard"></i> Dashboard</a> 
       </li> 

       <li> 
        <a href="javascript:;" data-toggle="collapse" data-target="#posts_dropdown"><i class="fa fa-fw fa-arrows-v"></i> posts <i class="fa fa-fw fa-caret-down"></i></a> 
        <ul id="posts_dropdown" class="collapse"> 
         <li> 
          <a href="#">view all pasts</a> 
         </li> 
         <li> 
          <a href="#">add posts</a> 
         </li> 
        </ul> 
       </li> 

       <li> 
        <a href="bootstrap-grid.html"><i class="fa fa-fw fa-wrench"></i> Categories</a> 
       </li> 


       <li> 
        <a href="blank-page.html"><i class="fa fa-fw fa-file"></i> Comments </a> 
       </li> 


       <li> 
        <a href="javascript:;" data-toggle="collapse" data-target="#demo"><i class="fa fa-fw fa-arrows-v"></i> Users <i class="fa fa-fw fa-caret-down"></i></a> 
        <ul id="demo" class="collapse"> 
         <li> 
          <a href="#">Dropdown Item</a> 
         </li> 
         <li> 
          <a href="#">Dropdown Item</a> 
         </li> 
        </ul> 
       </li> 


       <li> 
        <a href="index-rtl.html"><i class="fa fa-fw fa-dashboard"></i> Profile</a> 
       </li> 
      </ul> 
     </div> 



     <!-- /.navbar-collapse --> 
    </nav> 

    <div id="page-wrapper"> 

     <div class="container-fluid"> 




      <!-- Page Heading --> 
      <div class="row"> 
       <div class="col-lg-12"> 
        <h1 class="page-header"> 
         Welcome to Admin 
         <small> Rajsekhar</small> 
        </h1> 

        <div class="col-xs-6"> 
         <?php 

          if(isset($_POST['submit'])) 
          { 
           $cat_title = $_POST['cat_title']; 

           if ($cat_title == "" || empty($cat_title)) { 
            # code... 

            echo "this field should not be empty "; 
           } else { 

            $query = "INSERT INTO category(cat_title) VALUES ('{$cat_title}')"; 
            $create_cat_query = mysqli_query($connection,$query); 

            if(!$create_cat_query){ 

             die('query failed' . mysqli_error($connection)); 
            } 

           } 

          } 
         ?> 
         <form action="" method="POST"> 
          <div class="form-group"> 

           <label for="cat-title">Add Category</label> 
           <input type="text" class="form-control" name="cat_title"> 
          </div> 

          <div class="form-group"> 
           <input type="submit" name="submit" class="btn btn-primary" value="Add Category"> 
          </div> 

         </form> 
        </div> 


        <!-- Add category form --> 
        <div class="col-xs-6"> 

        <table class="table table-bordered table-hover"> 
        <thead> 
         <tr> 
          <th>Id</th> 
          <th>category title</th> 
         </tr> 
        </thead> 
        <tbody> 
        <?php 

         $query = "SELECT * FROM category;"; 
         $slect_all_category = mysqli_query($connection,$query); 
         while($row = mysqli_fetch_assoc($slect_all_category)){ 

         $cat_id = $row['cat_id']; 
         $cat_title = $row['cat_title']; 
         echo "<tr>"; 
         echo "<td> {$cat_id}</td>"; 
         echo "<td> {$cat_title}</td>"; 
         echo "<td> <a href = 'Categories.php?delete={$cat_id}'> Delete </a>"; 
         echo "</tr>"; 
         } 
         ?> 
         <tr> 

         </tr>      
        </tbody> 
        </table> 


        <?php 

         if(isset($_GET['delete'])) 
         { 
          $delete_id = $_GET['delete']; 

          $query = "DELETE FROM Category where cat_id = {$delete_id} "; 

          $delete_query = mysqli_query($connection,$query); 

         header("Location: Categories.php");  

          if(!$delete_query) 
          { 
           die('Query Failed' . mysqli_error($connection)); 
          } 


         } 

        ?> 



        </div> 
       </div> 
      </div> 
      <!-- /.row --> 

     </div> 
     <!-- /.container-fluid --> 

    </div> 
    <!-- /#page-wrapper --> 

Answer 1

頁面開始將您的文章的邏輯。

腳本的html部分一旦啓動，它就會自動開始將數據推送到瀏覽器，並且響應的標題應該首先出現。然後，你包括可能希望將錯誤返回給瀏覽器一些PHP文件，但產量已經開始，所以頭不能被修改，因此PHP給出了這樣的錯誤

<?php 

         if(isset($_GET['delete'])) 
         { 
          $delete_id = $_GET['delete']; 

          $query = "DELETE FROM Category where cat_id = {$delete_id} "; 

          $delete_query = mysqli_query($connection,$query); 

         header("Location: Categories.php");  

          if(!$delete_query) 
          { 
           die('Query Failed' . mysqli_error($connection)); 
          } 


         } 

        ?> 

//rest of the page