此购物车代码中的 php 代码错误

Question

我的代码中出现错误：-

<?php
session_start();
$page = 'index.php';
$connection = mysqli_connect("localhost","root","","cart");
if(mysqli_connect_errno())
{
    die("not connected to db ".mysqli_connect_error());
}
function product()
{
     $sql = "select id,name,description,price from products where quantity > 0 order by id DESC" ;
     $result = mysqli_query($connection,$sql);
     if(mysqli_num_rows($result))
     {
         echo 'no products to display';
     }
     else
     {
         while($row = mysqli_fetch_assoc($result))
         {
             echo '<div class="boxed">'.$row['name'].'<br>'.$row['price'].'<br>'.$row['description'].'<br>'.'</div>';
         }
     }
}
?>
<html>
<head>
<title>
</title>
<script>
.boxed {
  border: 1px solid green ;
}
</script>
</head>
<body>
<?php
product();
?>
</body>
</html>

错误是：

Notice: Undefined variable: connection in /Applications/XAMPP/xamppfiles/htdocs/cart.php on line 11

Warning: mysqli_query() expects parameter 1 to be mysqli, null given in /Applications/XAMPP/xamppfiles/htdocs/cart.php on line 11

Warning: mysqli_num_rows() expects parameter 1 to be mysqli_result, null given in /Applications/XAMPP/xamppfiles/htdocs/cart.php on line 12

Warning: mysqli_fetch_assoc() expects parameter 1 to be mysqli_result, null given in /Applications/XAMPP/xamppfiles/htdocs/cart.php on line 18

Answer 1

嗯，错误是正确的，$connection 无法从该函数访问。要使其在函数中可访问，您必须使用 global 关键字，如下所示：

function product()
{
    global $connection;
    ...
}

由于第一个错误，出现了其他错误。这也在 this 问题中得到了回答。

但这不是最佳实践，因为您可能无缘无故多次连接到数据库。我建议您使用单例 class 以确保您只有一个打开的数据库连接。 this 回答中对此进行了描述。

Answer 2

第一个答案是正确的，或者您可以像这样将 $connection 传递给您的函数：

<?php
session_start();
$page = 'index.php';
$connection = mysqli_connect("localhost","root","","cart");
function product($connection){
    $sql = "select id,name,description,price from products where quantity > 0 order by id DESC" ;
    $result = mysqli_query($connection,$sql);
    if(mysqli_num_rows($result))
    {
        echo 'no products to display';
    }
    else
    {
        while($row = mysqli_fetch_assoc($result))
        {
         echo '<div class="boxed">'.$row['name'].'<br>'.$row['price'].'<br>'.$row['description'].'<br>'.'</div>';
        }
    }
}

...

product($connection);

此购物车代码中的 php 代码错误

Error in php code in this cart code

php

mysqli

global-variables