PHP连接MySQL时出现Undefined variable $pdo错误求助

API 探路者

2026-7-4

问题分析与修复方案

错误根源

dbh.inc.php 语法错误：变量定义行末尾缺少分号，PHP解析失败，无法生成$pdo实例
PDO方法名大小写错误：setATTRibute应为setAttribute，大小写不匹配导致属性设置失败
连接错误未终止脚本：dbh.inc.php的catch块仅输出错误但未终止，导致formhandler.inc.php继续执行时$pdo未定义

修复后的代码

1. 修正 dbh.inc.php

<?php

$dsn = "mysql:host=localhost;dbname=myfirstdatabase";
$dbusername = "root";
$dbpassword = "root";

try {
    $pdo = new PDO($dsn, $dbusername, $dbpassword);
    $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
} catch (PDOException $e) {
    die("connection failed: " . $e->getMessage());
}

给$dbusername和$dbpassword的定义行添加分号
修正setATTRibute为标准写法setAttribute
用die()替代echo，确保连接失败时直接终止脚本，避免后续错误

2. 优化 formhandler.inc.php（可选）

<?php

if($_SERVER["REQUEST_METHOD"] == "POST" ) {
    $username = $_POST["username"];
    $pwd = $_POST["pwd"];
    $email = $_POST["email"];
    
    try {
        require_once "dbh.inc.php";

        $query  = "INSERT INTO users (username, pwd, email) VALUES (?, ?, ?);";

        $stmt = $pdo->prepare($query);
        $stmt->execute([$username, $pwd, $email]);

        $pdo = null;
        $stmt = null;
        header("Location: ../index.php");
        exit();
    } catch (PDOException $e) {
        die("query failed: " . $e->getMessage());
    }
} else {
    header("Location: ../index.php");
    exit();
}