php - 缺少“标头已发送” - 标头前的输出警告

Question

我知道有很多关于已经发送输出的标头的线程，但是我对我的 Debian VM 有一个奇怪的影响（PHP 版本 5.3.3-7+squeeze15）

以下代码有效，尽管它不应该有效！

<?php
echo "test";
header("Location:http://www.example.com");
?>

有人知道它为什么起作用而且我没有收到“标头已发送警告”吗？

Answer 1

从php.ini设置的文件注释中output_buffering：

; Output buffering is a mechanism for controlling how much output data
; (excluding headers and cookies) PHP should keep internally before pushing that
; data to the client. If your application's output exceeds this setting, PHP
; will send that data in chunks of roughly the size you specify.

; Turning on this setting and managing its maximum buffer size can yield some
; interesting side-effects depending on your application and web server.
; **You may be able to send headers and cookies after you've already sent output**
; through print or echo. You also may see performance benefits if your server is
; emitting less packets due to buffered output versus PHP streaming the output
; as it gets it. On production servers, 4096 bytes is a good setting for performance
; reasons.

Answer 2

尝试在回声后冲洗以使其不起作用

<?php
echo "test";
flush();
header("Location:http://www.example.com");
?>