PHP下对缓冲区的控制_PHP
PHP4.0 提供了一个输出缓冲函数集合。输出缓冲支持允许你写包裹函数功能压缩缓冲区。在 PHP4 的输出缓冲支持允许 HTML 头信息存放, 无论 HTML的正文是否输出。但在PHP中,头信息( (header(), content type, and cookies )不采用缓冲 。
在使用PHP的过程中不免要使用到header和setcookie两个函数,这两个函数会发送一段文件头信息给浏览器,但是如果在使用这两个函数之前已经有了任何输出(包括空输出,比如空格,回车和换行)就会提示出错,提示信息如下:“Header had all ready send by”!。在PHP 4.0里面加入了缓冲区控制的几个函数,使用这些函数可以帮我们解决很多问题。
函数名称 函数格式 功能 说明
Flush flush() 输出缓冲区内的内容并且删除缓冲区。 这个函数经常使用,效率很高。
ob_start void ob_start(void) 打开输出缓冲区。 当缓冲区激活时,所有来自PHP程序的非文件头信息均不会发送,而是保存在内部缓冲区。为了输出缓冲区的内容,可以使用ob_end_flush()或者使用ob_end_clean()来输出缓冲区的内容。
ob_get_contents string ob_get_contents(void) 返回内部缓冲区的内容。 这个函数会返回当前缓冲区中的内容,如果输出缓冲区没有激活,则返回 FALSE 。
ob_get_length int ob_get_length(void) 返回内部缓冲区的长度。 这个函数会返回当前缓冲区中的长度;和ob_get_contents一样,如果输出缓冲区没有激活。则返回 FALSE。
ob_end_flush void ob_end_flush(void) 发送内部缓冲区的内容到浏览器,并且关闭输出缓冲区。 这个函数发送输出缓冲区的内容(如果有的话)。
ob_end_clean void ob_end_clean(void) 删除内部缓冲区的内容,并且关闭内部缓冲区。 这个函数不会输出内部缓冲区的内容!
ob_implicit_flush void ob_implicit_flush ([int flag]) 打开或关闭绝对刷新 使用过Perl的人都知道$|=x的意义,这个字符串可以打开/关闭缓冲区,而ob_implicit_flush函数也和那个一样,默认为关闭缓冲区,打开绝对输出。
二、实例分析:
1、用缓冲区控制的函数防止文件头发送信息出错。
//PHP提示符
ob_start(); //打开缓冲区
echo "Welcome /n"; //输出
header("location:next.php"); //把浏览器重定向到next.php
?>
如果去掉ob_start,PHP就会提示在文件的第4行出错,出错信息为“Header had all ready send by”,但是加上ob_start,就不会提示出错,原因是当打开了缓冲区,echo后面的字符不会输出到浏览器,而是保留在服务器的缓冲区中,直到你使用flush或者ob_end_flush才会输出,所以并不会出现文件头已输出的错误!
2、保存输出(这是一个很经典的用途)。
假如你想知道客户端的屏幕输出信息像函数的输出结果等,而且这个输出信息会因客户端的不同而不同。我们可以用函数 phpinfo(); ?> 得到服务器的设置信息,但是如果想要保存phpinfo()函数的输出怎么办呢?在没有缓冲区控制之前,可以说一点办法也没有,但是有了缓冲区的控制,我们可以轻松的解决。
ob_start(); //打开缓冲区
phpinfo(); //使用phpinfo函数
$info=ob_get_contents(); //得到缓冲区的内容并且赋值给$info
$file=fopen('phpinfo.txt','w'); //打开文件phpinfo.txt
fwrite($file,$info); //写入信息到phpinfo.txt
fclose($file); //关闭文件phpinfo.txt
?>
用以上的方法,就可以把不同用户的phpinfo信息保存下来,这在以前恐怕没有办法办到!同样,用缓冲区的方法可以保存一般方法难以完成的任务,这其实上就是将一些“过程”转化为“函数”的方法。

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