php - 缺少 "headers already sent"- header 前的输出警告

Question

我知道有很多关于 header 的线程已经发送了输出，但是我对我的 Debian VM(PHP 版本 5.3.3-7+squeeze15)产生了奇怪的影响

下面的代码可以工作，但它不应该工作!

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

有谁知道为什么它可以工作并且我没有收到“ header 已发送警告”？

Answer 1

来自 php.ini 文件对设置 output_buffering 的注释:

; 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.