所以我有这个PHP代码但是在使用时我得到“使用未定义的常量mysqli - 假设'mysqli'”错误和致命错误：未捕获错误：调用未定义函数connect（）
这是PHP代码：
<?php
if (isset($_POST['submit'])) {
include_once 'dbh.inc.php';
$last = mysqli_real_escape_string($conn, $_POST['last']);
$email = mysqli_real_escape_string($conn, $_POST['email']);
$uid = mysqli_real_escape_string($conn, $_POST['uid']);
$pwd = mysqli_real_escape_string($conn, $_POST['pwd']);
if (empty($first) || empty($last) || empty($email) || empty($uid) || empty($pwd)) {
header("Location: ../signup.php?signup=empty");
exit();
} else {
//Check if input characters are valid
if (!preg_match("/^[a-zA-Z]*$/", $first) || !preg_match("/^[a-zA-Z]*$/", $last)) {
header("Location: ../signup.php?signup=invalid");
exit();
} else {
//Check if email is valid
if (!filter_var($email, FILTER_VALIDATE_EMAIL)) {
header("Location: ../signup.php?signup=email");
exit();
} else {
$sql = "SELECT * FROM users WHERE user_uid='$uid'";
$result = mysqli_query($conn, $sql);
$resultCheck = mysqli_num_rows($result);
if ($resultCheck > 0) {
header("Location: ../signup.php?signup=invalid");
exit();
} else {
//Hashing the password
$hashedPwd = password_hash($pwd, PASSWORD_DEFAULT);
//Insert the user into the database
$sql = "INSERT INTO users (user_first, user_last, user_email, user_uid, user_pwd) VALUES ('$first', '$last', '$email', '$uid', '$hashedPwd');";
mysqli_query($conn, $sql);
header("Location: ../signup.php?signup=success");
exit();
}
}
}
}
} else {
header("Location: ../signup.php");
exit();
}
?>