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php中ob_flush与flush的区别
ob_flush/flush在php手册中的描述:都是刷新输出缓冲区, 并且还需要配套使用。
其实,它们的操作对象不同,有些情况下,flush根本不做什么事情。
ob_*系列函数, 是操作PHP本身的输出缓冲区。

所以, ob_flush是刷新PHP自身的缓冲区。而flush, 严格来讲, 这个只有在PHP做为apache的Module(handler或者filter)安装的时候, 才有实际作用. 它是刷新WebServer(可以认为特指apache)的缓冲区。

在apache module的sapi下, flush会通过调用sapi_module的flush成员函数指针, 间接的调用apache的api: ap_rflush刷新apache的输出缓冲区, 当然手册中也说了, 有一些apache的其他模块, 可能会改变这个动作的结果。

有些Apache的模块,比如mod_gzip,可能自己进行输出缓存,这将导致flush()函数产生的结果不会立即被发送到客户端浏览器。

甚至浏览器也会在显示之前,缓存接收到的内容。例如 Netscape浏览器会在接受到换行或 html 标记的开头之前缓存内容,并且在接受到 标记之前,不会显示出整个表格。
一些版本的 Microsoft Internet Explorer 只有当接受到的256个字节以后才开始显示该页面,所以必须发送一些额外的空格来让这些浏览器显示页面内容。

所以, 正确使用俩者的顺序是. 先ob_flush, 然后flush,如果Web服务器的操作系统是windows系统,那顺序颠倒或者不使用ob_flush()也不会出现问题。但是在Linux系统上就无法刷新输出缓冲。

当然, 在其他sapi下, 不调用flush也可以, 只不过为了保证你代码的可移植性, 建议配套使用。

根据以上描述,进行如下的测试:
测试1,

<?php
ob_start();
echo '1';
ob_flush();//输出php缓存并刷新
echo '2';
ob_flush();//输出php缓存并刷新
$cc = ob_get_contents();
ob_end_clean();
var_dump()($cc);
?>

输出:
12string(0) ""

测试2:
<?php
ob_start();
echo '1';
flush();     //输出apache缓存并刷新
echo '2';
flush();     //输出apache缓存并刷新
$cc = ob_get_contents();
ob_end_clean();
var_dump($cc);
//by www.jbxue.com
?>

输出:
string(2) "12"

测试3:
<?php
ob_start();
echo '1';
ob_flush();//输出php缓存并刷新
flush();//输出apache缓存并刷新
echo '2';
ob_flush();//输出php缓存并刷新
flush();//输出apache缓存并刷新
$cc = ob_get_contents();
ob_end_clean();
var_dump($cc);
//by www.jbxue.com
?>

输出:
12string(0) ""

测试4,
<?php
ob_start();
echo '1';
flush();//输出apache缓存并刷新
ob_flush();//输出php缓存并刷新
echo '2';
flush();//输出apache缓存并刷新
ob_flush();//输出php缓存并刷新
$cc = ob_get_contents();
ob_end_clean();
var_dump($cc);
?>

输出:
12string(0) ""
本文出处参考:http://www.jbxue.com/article/9469.html

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