php中ob_get_contents();ob_end_clean();ob_start();用法详解

php缓存相关函数：
ob_get_contents();
ob_end_clean();
ob_start()

使用ob_start()把输出那同输出到缓冲区，而不是到浏览器。
然后用ob_get_contents得到缓冲区的数据。

ob_start()在服务器打开一个缓冲区来保存所有的输出。
因此，在任何时候使用echo ，输出都将被加入缓冲区中，直到程序运行结束或者使用ob_flush()来结束。
然后在服务器中缓冲区的内容才会发送到浏览器，由浏览器来解析显示。

函数ob_end_clean 会清除缓冲区的内容，并将缓冲区关闭，但不会输出内容。
此时得用一个函数ob_get_contents()在ob_end_clean()前面来获得缓冲区的内容。
这样的话，能将在执行ob_end_clean()前把内容保存到一个变量中，然后在ob_end_clean()后面对这个变量做操作。

例子：
 

<?php
ob_start(); // buf1
echo ' multiple ';
ob_start(); // buf2
echo ' buffers work ';
$buf2 = ob_get_contents();
ob_end_clean();
$buf1 = ob_get_contents();
ob_end_clean();

echo $buf1;
echo '<br/>';
echo $buf2;
?>

下面来看，ob_get_contents

(PHP 4, PHP 5)
ob_get_contents -- Return the contents of the output buffer
Description
string ob_get_contents ( void )

This will return the contents of the output buffer or FALSE, if output buffering isn't active.

See also ob_start() and ob_get_length().

if you use ob_start with a callback function as a parameter, and that function changes ob string (as in example in manual) don't expect that ob_get_contents will return changed ob.
it will work as you would use ob_start with no parameter at all. So don't be confused.
transfer image, another method (alternative to fsockopen or function socket) :

server(192.168.0.1)
makeimage.php
 

<?php
...........
...........
$nameimage="xxxx.jpg"
$comand=exec("plotvelocity.sh $nameimage $paramater1 $paramater2");
ob_start();
readfile($nameimage);
$image_data = ob_get_contents();
ob_end_clean();
echo $image_data;
unlink($nameimage);

Client (192.168.0.2)
$bild="images/newimage2.gif";
$host="192.168.0.1";
$url=file_get_contents("http://$host/makeimage.php?$querystring");
$fp = fopen("$bild", 'wb');
fwrite($fp, $url);
fclose($fp);
echo '<img src="'.$bild.'">';
?>

naturally you can transfer whichever thing and not only images

ob_get_clean

(PHP 4 >= 4.3.0, PHP 5)
ob_get_clean -- Get current buffer contents and delete current output buffer
Description
string ob_get_clean ( void )

This will return the contents of the output buffer and end output buffering. If output buffering isn't active then FALSE is returned. ob_get_clean() essentially executes both ob_get_contents() and ob_end_clean().

例1：
ob_get_clean()的简单示例
 

<?php

ob_start();

echo "Hello World";

$out = ob_get_clean();
$out = strtolower($out);

var_dump($out);
?>

输出: string(11) "hello world"

例2，ob_start() and ob_get_contents().
Notice that the function beneath does not catch errors, so throw in an @ before those ob_* calls
Running PHP4 < 4.3.0, you can simply add the following to use the function anyway:
 

<?php
if (!function_exists("ob_get_clean")) {
function ob_get_clean() {
$ob_contents = ob_get_contents();
ob_end_clean();
return $ob_contents;
}
} //by www.jb200.com
?>