php 写入文件乱码

// 设置 PHP 文件编码为 UTF-8
header('Content-Type: text/html; charset=utf-8');

$data = "你好，世界！";
$filename = "output.txt";

// 打开文件并指定编码
$handle = fopen($filename, 'w');
fwrite($handle, $data);
fclose($handle);

// 连接数据库并设置编码
$mysqli = new mysqli("localhost", "username", "password", "database");
$mysqli->set_charset("utf8");

// 查询数据
$result = $mysqli->query("SELECT * FROM table_name");

// 写入文件
$handle = fopen("output.txt", 'w');
while ($row = $result->fetch_assoc()) {
    fwrite($handle, $row['column_name']);
}
fclose($handle);
$mysqli->close();

<?php
header('Content-Type: text/html; charset=utf-8');

$data = "你好，世界！";
$filename = "output.txt";

// 打开文件并指定编码
$handle = fopen($filename, 'w');
if ($handle) {
    fwrite($handle, $data);
    fclose($handle);
} else {
    echo "无法打开文件";
}
?>