PHP有一个空白屏幕

这是我的密码

<? 
  define('DB_HOST', 'localhost'); 
  define('DB_NAME', 'practice'); 
  define('DB_USER','root'); 
  define('DB_PASSWORD',''); 
  $con=mysql_connect(DB_HOST,DB_USER,DB_PASSWORD) or die("Failed to connect to MySQL: " . mysql_error()); 
  $db=mysql_select_db(DB_NAME,$con) or die("Failed to connect to MySQL: " . mysql_error()); 
  /* $ID = $_POST['user']; $Password = $_POST['pass']; */ 
  function SignIn() { 
      session_start(); //starting the session for user profile page 
      if(!empty($_POST['user'])) //checking the 'user' name which is from Sign-In.html, is it empty or have some text 
      { 
          $query = mysql_query("SELECT * FROM UserName where userName = '$_POST[user]' AND pass = '$_POST[pass]'") or die(mysql_error()); 
          $row = mysql_fetch_array($query) or die(mysql_error()); 
          if(!empty($row['userName']) AND !empty($row['pass'])) { 
             $_SESSION['userName'] = $row['pass']; echo "SUCCESSFULLY LOGIN TO USER PROFILE PAGE..."; 
          } else { 
             echo "SORRY... YOU ENTERD WRONG ID AND PASSWORD... PLEASE RETRY..."; 
          } 
    } 
 } 
 if(isset($_POST['submit'])) { SignIn(); } 
 ?>

您错过了函数SignIn（）

的右大括号}，它会为其生成语法错误

您的代码（有错误）：

---

我投了反对票，因为如果我们无法阅读您的代码，我们就无法帮助您。如果您正在编写新代码，请不要使用
mysql.*
函数。它们是旧的、破损的，在PHP5.5中被弃用（它太旧了，甚至不再接收安全更新），在PHP7中被完全删除。使用或与准备好的语句和参数绑定一起使用。有关详细信息，请参阅。当您看到一个空白屏幕（但您不希望看到它）时，请在发布问题之前检查您的错误日志。关于您关于
session\u start（）
的声明，我不同意，它很可能位于执行路径的最下方，因为您尚未发送输出，有一组匹配的打开和关闭，它不会。为什么？我已经安装了PHP环境。它没有显示任何内容。@Majid Fouladpour:我从来没有说过它不能使用，我说过session_start（）；应在开始时调用以避免错误。根据我的经验，我看到很多网站都有通知，因为在使用
session\u start（）
@ChanakanZ程序员之前抛出了一些错误：您使用的是PHP短标记，要使用它，必须在PHP.ini中启用短标记。有关此配置的更多详细信息，请参阅
<?
  define('DB_HOST', 'localhost'); 
  define('DB_NAME', 'practice'); 
  define('DB_USER','root'); 
  define('DB_PASSWORD',''); 
  $con = mysql_connect(DB_HOST,DB_USER,DB_PASSWORD) or die("Failed to connect to MySQL: " . mysql_error());
  $db = mysql_select_db(DB_NAME, $con) or die("Failed to connect to MySQL: " . mysql_error());
  /* $ID = $_POST['user']; $Password = $_POST['pass']; */
  function SignIn() {
    session_start(); //starting the session for user profile page if(!empty($_POST['user'])) //checking the 'user' name which is from Sign-In.html, is it empty or have some text { $query = mysql_query("SELECT * FROM UserName where userName = '$_POST[user]' AND pass = '$_POST[pass]'") or die(mysql_error()); $row = mysql_fetch_array($query) or die(mysql_error()); if(!empty($row['userName']) AND !empty($row['pass'])) { $_SESSION['userName'] = $row['pass']; echo "SUCCESSFULLY LOGIN TO USER PROFILE PAGE..."; } else { echo "SORRY... YOU ENTERD WRONG ID AND PASSWORD... PLEASE RETRY..."; } } } if(isset($_POST['submit'])) { SignIn(); } 
?>

<?
  define('DB_HOST', 'localhost'); 
  define('DB_NAME', 'practice'); 
  define('DB_USER','root'); 
  define('DB_PASSWORD',''); 
  $con = mysql_connect(DB_HOST,DB_USER,DB_PASSWORD) or die("Failed to connect to MySQL: " . mysql_error());
  $db = mysql_select_db(DB_NAME, $con) or die("Failed to connect to MySQL: " . mysql_error());
  /* $ID = $_POST['user']; $Password = $_POST['pass']; */
  function SignIn() {
    session_start(); //starting the session for user profile page if(!empty($_POST['user'])) //checking the 'user' name which is from Sign-In.html, is it empty or have some text { $query = mysql_query("SELECT * FROM UserName where userName = '$_POST[user]' AND pass = '$_POST[pass]'") or die(mysql_error()); $row = mysql_fetch_array($query) or die(mysql_error()); if(!empty($row['userName']) AND !empty($row['pass'])) { $_SESSION['userName'] = $row['pass']; echo "SUCCESSFULLY LOGIN TO USER PROFILE PAGE..."; } else { echo "SORRY... YOU ENTERD WRONG ID AND PASSWORD... PLEASE RETRY..."; } } } if(isset($_POST['submit'])) { SignIn(); }
  }
?>

<?php
  ini_set('display_errors', 'On');
  error_reporting(E_ALL);
?>