获取未定义的变量：index.php中的pdo

我正在创建配方数据库，添加“添加”和“删除”功能后，系统会抛出一个错误：

注意：未定义的变量：第52行C:\xampp\htdocs\COMP1321\recipes\index.php中的pdo 致命错误：未捕获错误：在C:\xampp\htdocs\COMP1321\recipes\index.php:52堆栈跟踪：#0{main}中，在第52行的C:\xampp\htdocs\COMP1321\recipes\index.php中调用null上的成员函数query（）

Index.php

try // selection block
{
    $sql = 'SELECT * FROM recipe';
    $result = $pdo->query($sql);
} 

<?php
try
{
    //new PDO('mysql:host=mysql.cms.gre.ac.uk; dbname=mdb_', '', '');
    $pdo = new PDO('mysql:host=localhost; dbname=mdb_recipes', 'root', ''); 
    $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    $pdo->exec('SET NAMES "utf8"');

} catch (PDOException $e) {

    $error = 'Unable to connect to database server';
    include 'error.html.php';
    exit();
}

<?php

if(isset($_GET['addrecipe'])) {
    include 'form.html.php';
    exit();
}
//insert block
if (isset($_POST['recipename'])) {
include 'admin/includes/db.inc.php';
try
{
    //prepared statement
    $sql = 'INSERT INTO recipe SET
        recipename = :recipename,
        recipedate = CURDATE()';
    $s = $pdo->prepare($sql);
    $s->bindValue(':recipename', $_POST['recipename']);
    $s->execute();
} catch (PDOException $e) {
    $error = 'Error adding submitted recipe' . $e->getMessage();
    include 'error.html.php';
    exit();
}
header('Location: .');
exit();
}

//delete block
if(isset($_GET['deleterecipe']))
{
    include '../includes/db.inc.php';
    try
    {
        $sql = 'DELETE FROM recipe WHERE id = :id';
        $s = $pdo->prepare($sql);
        $s->bindValue(':id', $_POST['id']);
        $s->execute();
    }
    catch (PDOException $e)
    {
        $error = 'Error deleting recipe' . $e->getMessage();
        include 'error.html.php';
        exit();
    }
    header('Location: .');
    exit();
}

try // selection block
{
    $sql = 'SELECT * FROM recipe';
    $result = $pdo->query($sql);
} 
catch (PDOException $e) {
    $error = 'Error fetching recipes' . $e->getMessage();
    include 'error.html.php';
    exit();
}

foreach ($result as $row) {
    $recipes[] = array(
        'id' => $row['id'],
        'recipename' => $row['recipename'],
        'time' => $row['time'],
        'ingredients' => $row['ingredients'],
        'recipetext' => $row['recipetext'],
        'servings' => $row['servings'],
        'nutritionfacts' => $row['nutritionfacts'],
        'recipedate' => $row['recipedate'],
        'image' => $row['image'],
    );
}
include 'recipes.html.php';

Databaseconnection.inc.php

try // selection block
{
    $sql = 'SELECT * FROM recipe';
    $result = $pdo->query($sql);
} 

<?php
try
{
    //new PDO('mysql:host=mysql.cms.gre.ac.uk; dbname=mdb_', '', '');
    $pdo = new PDO('mysql:host=localhost; dbname=mdb_recipes', 'root', ''); 
    $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    $pdo->exec('SET NAMES "utf8"');

} catch (PDOException $e) {

    $error = 'Unable to connect to database server';
    include 'error.html.php';
    exit();
}

<?php

if(isset($_GET['addrecipe'])) {
    include 'form.html.php';
    exit();
}
//insert block
if (isset($_POST['recipename'])) {
include 'admin/includes/db.inc.php';
try
{
    //prepared statement
    $sql = 'INSERT INTO recipe SET
        recipename = :recipename,
        recipedate = CURDATE()';
    $s = $pdo->prepare($sql);
    $s->bindValue(':recipename', $_POST['recipename']);
    $s->execute();
} catch (PDOException $e) {
    $error = 'Error adding submitted recipe' . $e->getMessage();
    include 'error.html.php';
    exit();
}
header('Location: .');
exit();
}

//delete block
if(isset($_GET['deleterecipe']))
{
    include '../includes/db.inc.php';
    try
    {
        $sql = 'DELETE FROM recipe WHERE id = :id';
        $s = $pdo->prepare($sql);
        $s->bindValue(':id', $_POST['id']);
        $s->execute();
    }
    catch (PDOException $e)
    {
        $error = 'Error deleting recipe' . $e->getMessage();
        include 'error.html.php';
        exit();
    }
    header('Location: .');
    exit();
}

try // selection block
{
    $sql = 'SELECT * FROM recipe';
    $result = $pdo->query($sql);
} 
catch (PDOException $e) {
    $error = 'Error fetching recipes' . $e->getMessage();
    include 'error.html.php';
    exit();
}

foreach ($result as $row) {
    $recipes[] = array(
        'id' => $row['id'],
        'recipename' => $row['recipename'],
        'time' => $row['time'],
        'ingredients' => $row['ingredients'],
        'recipetext' => $row['recipetext'],
        'servings' => $row['servings'],
        'nutritionfacts' => $row['nutritionfacts'],
        'recipedate' => $row['recipedate'],
        'image' => $row['image'],
    );
}
include 'recipes.html.php';

---

看起来您从未包含数据库连接文件

如果未设置
$\u POST['recipename']
，并且未设置
$\u GET['deleterecipe']
，那么当您到达该行时，
db.inc.php
从未包含在内，因此未定义
$pdo
。
您需要移动
包含'admin/includes/db.inc.php'行位于form.html.php include的正下方

这将使其可用于整个页面，因为它是必需的，无论您是否插入或删除配方，因为您需要它用于底部的选择块

每个页面只需要包含一次文件，我通常会在DB和其他类似的全局依赖项的文件顶部使用
require_once（）
，而不是尝试在每个需要的位置包含它，每个文件包含3次以上，然后不必要地包含该文件，并可能生成警告或错误。一般来说，这只会使代码更加复杂。这是一个共享资源，让它共享吧。或者创建一个单例，以标准方式为您创建或检索PDO实例，这样您只有一个PDO连接，而不是每个请求可能有多个连接。
您是否在try/catch块的外部（之前）声明了
$PDO
变量，以便它在index.php文件中可见？这两个
if（isset（$\u POST['recipename'））
和
if（isset（$\u GET['deleterecipe']）
必须为false，因此您永远不会包含数据库文件。这是错误的。不要在文件的顶部包含一次，否则会损害你的理智。