未定义的变量:con in C:xampphtdocsCRUDlogin.php 在第 14 行 - Undefined variable: con in C:xampphtdocsCRUDlogin.php on line 14

Undefined variable: con in C:xampphtdocsCRUDlogin.php on line 14

<?php
    $con = mysqli_connect('localhost', 'root', '', 'crud_db');
    if (mysqli_connect_errno()) 
    {
      echo "Failed to connect to MySQL: " . mysqli_connect_error();
    }
    function signin() 
    {
      $session_start;
      if (!empty($_POST['email'])) 
      {
        echo "not empty";
        $query = "SELECT * FROM 'employee' where email= '$_POST ['email']' AND password=   '$_POST ['pwd']'";
        $result = mysqli_query($con, $query);
        $row = mysqli_fetch_array($result);
        if (!empty($row['email']) AND !empty($row['password'])) {
            echo "successfully login";
        } else {
            echo "login fail";
      }
    }
    }
    if (isset($_POST['submit'])) 
    {
      signin();
    }
?>

我是php的新手，我正在尝试创建一个简单的登录页面这是我的PHP代码，一个简单的登录PHP代码。当我尝试运行代码时，出现错误注意：未定义的变量：con in C：''xampp''htdocs''CRUD''login.php 在第 14 行我已经在第一行定义了变量$con，那么为什么我会收到此错误。

第二 - 当我尝试运行 sinin 功能块时，出现错误警告：mysqli_fetch_array(( 期望参数 1 mysqli_result，在第 15 行的 C：''xampp''htdocs''CRUD''login.php 中给出空这是什么意思，我该如何解决这个问题。

与

问题无关，但：

 $query = "SELECT * FROM 'employee' where email= '$_POST ['email']' AND password=   '$_POST ['pwd']'";

行不通。

$query = "SELECT * FROM 'employee' where email= '{$_POST ['email']}' AND password=   '{$_POST['pwd']}'";

将起作用，但它仍然容易受到SQL注入的攻击。

阅读如何防止 PHP 中的 SQL 注入？

您可以在函数中将其设置为全局，也可以在参数中传递它以访问它

$con = mysqli_connect('localhost', 'root', '', 'crud_db');
if (mysqli_connect_errno()) 
{
  echo "Failed to connect to MySQL: " . mysqli_connect_error();
}
function signin($con) 
{
  session_start();
  if (!empty($_POST['email'])) 
  {
    echo "not empty";
    $query = "SELECT * FROM employee where email= '$_POST ['email']' AND password=   '$_POST ['pwd']'";
    $result = mysqli_query($con, $query);
    $row = mysqli_fetch_array($result);
    if (!empty($row['email']) AND !empty($row['password'])) {
        echo "successfully login";
    } else {
        echo "login fail";
  }
}
}
if (isset($_POST['submit'])) 
{
  signin($con);
}
?>

像

这样用不同的 php 脚本编写数据库端和函数端，它可能会起作用

<?php 
$con = mysqli_connect('localhost', 'root', '', 'crud_db');
?>
function.php
<?php
include('database.php');
function signin() 
{
global $con;
  session_start();
  if (!empty($_POST['email'])) 
  {
    echo "not empty";
    $query = "SELECT * FROM employee where email= '$_POST ['email']' AND password=   '$_POST ['pwd']'";
    $result = mysqli_query($con, $query);
    $row = mysqli_fetch_array($result);
    if (!empty($row['email']) AND !empty($row['password'])) {
        echo "successfully login";
    } else {
        echo "login fail";
  }
}
}

?>