<form action="process.php" method="post">
    <input type="text" name="username">
    <input type="submit" value="提交">
</form>

<?php
if ($_SERVER["REQUEST_METHOD"] == "POST") {
    $username = $_POST['username'];
    // 处理数据...
    header("Location: success.php");
    exit;
}
?>

if ($_SERVER["REQUEST_METHOD"] == "POST" && !empty($_POST['username'])) {
    // 处理数据...
    header("Location: success.php");
    exit;
}

// 使用绝对URL路径
header("Location: http://example.com/success.php");
// 或者使用基于根目录的相对路径
header("Location: /success.php");

header("Location: success.php");
exit; // 必须添加

<?php
if ($_SERVER["REQUEST_METHOD"] == "POST") {
    // 验证数据
    if (empty($_POST['username'])) {
        header("Location: form.php?error=1");
        exit;
    }
    
    // 处理数据
    $username = htmlspecialchars($_POST['username']);
    
    // 重定向
    header("Location: success.php");
    exit;
}
?>

session_start();
if ($_SERVER["REQUEST_METHOD"] == "POST") {
    $_SESSION['form_data'] = $_POST;
    header("Location: process.php");
    exit;
}

session_start();
if ($_SERVER["REQUEST_METHOD"] == "POST") {
    if ($_SESSION['token'] !== $_POST['token']) {
        header("Location: form.php?error=token");
        exit;
    }
    // 处理数据...
    header("Location: success.php");
    exit;
}