PHP 7.2-包含文件无法访问另一个包含文件

我在一个包含文件访问另一个包含文件（我的数据库连接）时遇到问题

我有一个布局如下的站点：

root/conn.php :: db connection file  
root/site/file1.php :: regular page  
root/site/include/func.inc :: file with functions in it

下面列出了每个文件以及相应的代码

conn.php:：

<?php

$host = 'localhost';
$db   = 'mydb';
$user = 'myuser';
$pass = 'mypass';
$charset = 'utf8mb4';

mysqli_report(MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT);
try {
    $conn = new mysqli($host, $user, $pass, $db);
    $conn->set_charset($charset);
} catch (\mysqli_sql_exception $e) {
     throw new \mysqli_sql_exception($e->getMessage(), $e->getCode());
}
unset($host, $db, $user, $pass, $charset);

?>

---

func.inc:：

include_once ("{$_SERVER['DOCUMENT_ROOT']}/conn.php");
{ various functions }

---

当我浏览到/file1.php时，出现以下错误：

PHP Notice:  Undefined variable: conn in C:\inetpub\root\site\include\func.inc on line 231
PHP Fatal error:  Uncaught Error: Call to a member function prepare() on null in C:\inetpub\root\site\include\func.inc:231

---

我的func.inc文件似乎找不到conn.php文件。我还尝试从func.inc中删除include函数。/include文件夹中还有其他文件可以使用相同的include函数访问conn.php文件

这个问题与称为

变量范围的东西有关
==>请阅读以获取详细信息

第二个例子描述了您的问题

func公司
PHP Notice:  Undefined variable: conn in C:\inetpub\root\site\include\func.inc on line 231
PHP Fatal error:  Uncaught Error: Call to a member function prepare() on null in C:\inetpub\root\site\include\func.inc:231

<?php
include_once ("{$_SERVER['DOCUMENT_ROOT']}/conn.php");    
// to illustrate the issue, the include can be simplified to 
// $conn = "something";  // => global scope variable

function myFunc(){
    echo $conn; //no output - $conn exists ONLY in the local scope --> not available inside thisfunction
}

<?php
function myFunc($conn){
    echo $conn; //outputs $conn
}

<?php
include_once ("{$_SERVER['DOCUMENT_ROOT']}/conn.php");
include_once ("{$_SERVER['DOCUMENT_ROOT']}/site/include/func.inc");

//call function and pass the $conn, it's available here in the global scope
myFunc($conn); 

<?php
include_once ("{$_SERVER['DOCUMENT_ROOT']}/conn.php");    

function myFunc(){
    global $conn; //$conn is declared global in the local scope of this function
    echo $conn; //outputs $conn from conn.php if you call myFunc from anywhere
}