Ob_start usage analysis in PHP

This article mainly introduces the usage analysis of ob_start in PHP, which has certain reference value. Now I share it with everyone. Friends in need can refer to it

Use PHP's ob_start();
Control your browser cache

Output Control Functions allow you to freely control the output of data in your script. It is very useful, especially when you want to output the file header after the data has been output. The output control function is not used header() or setcookie(), the file header information sent has an effect, and only affects those data blocks similar to echo() and PHP code.
Let’s give a simple example first to give everyone a general impression of Output Control:
Example 1.

Program codeProgram code

<?php
ob_start(); //打开缓冲区
echo \"Hellon\"; //输出
header("location:index.php"); //把浏览器重定向到index.php
ob_end_flush();//输出全部内容到浏览器
?>

All pairs Anyone who knows the header() function knows that this function will send a file header to the browser, but if there is any output (including empty output, such as spaces, carriage returns, and line feeds) before using this function, it will prompt Something went wrong. If we remove ob_start() in the first line and then execute this program, we will find that we get an error message: "Header had all ready to send by"! But adding ob_start will not prompt an error. The reason is that when the buffer is opened, the characters after echo will not be output to the browser, but will be retained on the server until you use Only flush or ob_end_flush will output, so there will not be any file header output errors!

1. Introduction to related functions:
1. Flush: refresh the contents of the buffer and output.
Function format: flush()
Description: This function is frequently used and is very efficient.
2. ob_start: Open the output buffer
Function format: void ob_start(void)
Description: When the buffer is activated, all non-file header information from the PHP program will not be sent, but saved. in the internal buffer. In order to output the contents of the buffer, you can use ob_end_flush() or flush() to output the contents of the buffer.
3, ob_get_contents: Return the contents of the internal buffer.
Usage: string ob_get_contents(void)
Description: This function will return the contents of the current buffer. If the output buffer is not activated, it will return FALSE.
4. ob_get_length: Returns the length of the internal buffer.
Usage: int ob_get_length(void)
Description: This function will return the length in the current buffer; the same as ob_get_contents, if the output buffer is not activated. then returns FALSE.
5. ob_end_flush: Send the contents of the internal buffer to the browser and close the output buffer.
Usage: void ob_end_flush(void)
Description: This function sends the contents of the output buffer (if any).
6. ob_end_clean: Delete the contents of the internal buffer and close the internal buffer
Usage method: void ob_end_clean(void)
Description: This function will not output the contents of the internal buffer but delete it. !
7. ob_implicit_flush: Turn on or turn off absolute refresh
Usage method: void ob_implicit_flush ([int flag])
Description: Anyone who has used Perl knows the meaning of $|=x, this string can be turned on /Close the buffer, and the ob_implicit_flush function is the same as that. The default is to close the buffer. After turning on absolute output, each script output is sent directly to the browser, and there is no need to call flush()

2. In-depth understanding:

1. About the Flush function:
This function appeared in PHP3. It is a very efficient function. It has a very useful function of refreshing the browser's cache. Let's take the example An example with very obvious running effect to illustrate flush.
Example 2.

Program codeProgram code

<?php
for($i = 1; $i <= 300; $i++ ) print(" ");
// 这一句话非常关键，cache的结构使得它的内容只有达到一定的大小才能从浏览器里输出
// 换言之，如果cache的内容不达到一定的大小，它是不会在程序执行完毕前输出的。经
// 过测试，我发现这个大小的底限是256个字符长。这意味着cache以后接收的内容都会
// 源源不断的被发送出去。
For($j = 1; $j <= 20; $j++) {
echo $j."
";
flush(); //这一部会使cache新增的内容被挤出去，显示到浏览器上
sleep(1); //让程序"睡"一秒钟，会让你把效果看得更清楚
}
?>

Note: If you add ob_implicit_flush() at the beginning of the program to turn on the absolute By refreshing, you can no longer use flush() in the program. The benefit of this is: improve efficiency!

2. Regarding the ob series functions:
I would like to quote an example from my good friend y10k first:
Example 3.

For example, you can use the server and client settings information, but this information will vary depending on the client. What if you want to save the output of the phpinfo() function? Before there was no buffer control, it can be said that there was no way at all, but with buffer control, we can easily solve it:
Program codeProgram code

<?php
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
$file=fopen(\&#39;info.txt\&#39;,\&#39;w\&#39;); //打开文件info.txt
fwrite($file,$info); //写入信息到info.txt
fclose($file); //关闭文件info.txt
?>

Use the above method, You can save the phpinfo information of different users, which I am afraid there was no way to do before! In fact, the above is a method to convert some "processes" into "functions"!
Some people may ask: "Is it just like this? Are there any other uses?" Of course there are, such as PHP in the author's forum Syntax highlighting is related to this (PHP's default syntax highlighting function will output directly and cannot save the results. If it is displayed every time it is called, it will be a waste of CPU. The author's forum will display the results of the syntax highlighting function. Retained by controlling the buffer), if you are interested, you can take a look

可能现在大家对ob_start()的功能有了一定的了解，上面的一个例子看似简单，但实际上已经掌握了使用ob_start()的要点。
<1>.使用ob_start打开browser的cache，这样可以保证cache的内容在你调用flush(),ob_end_flush()（或程序执行完毕）之前不会被输出。
<2>.现在的你应该知道你所拥有的优势：可以在任何输出内容后面使用header,setcookie以及session，这是 ob_start一个很大的特点；也可以使用ob_start的参数，在cache被写入后，然后自动运行命令，比如ob_start(\ "ob_gzhandler\")；而我们最常用的做法是用ob_get_contents()得到cache中的内容，然后再进行处理……
<3>.当处理完毕后，我们可以使用各种方法输出，flush(),ob_end_flush(),以及等到程序执行完毕后的自动输出。当然，如果你用的是ob_get_contents()，那么就要你自己控制输出方式了。

来，让我们看看能用ob系列函数做些什么……

一、 静态模版技术

简介：所谓静态模版技术就是通过某种方式，使得用户在client端得到的是由PHP产生的html页面。如果这个html页面不会再被更新，那么当另外的用户再次浏览此页面时，程序将不会再调用PHP以及相关的数据库，对于某些信息量比较大的网站，例如sina,163,sohu。类似这种的技术带来的好处是非常巨大的。

我所知道的实现静态输出的有两种办法：
<1>.通过y10k修改的phplib的一个叫template.inc.php类实现。
<2>.使用ob系列函数实现。
对于第一种方法，因为不是这篇文章所要研究的问题，所以不再赘述。
我们现在来看一看第二种方法的具体实现：
Example 4.

程序代码 程序代码

<?php
ob_start();//打开缓冲区
?>
php页面的全部输出
<?
$content = ob_get_contents();//取得php页面输出的全部内容
$fp = fopen("output00001.html", "w"); //创建一个文件，并打开，准备写入
fwrite($fp, $content); //把php页面的内容全部写入output00001.html，然后……
fclose($fp);
?>

这样，所谓的静态模版就很容易的被实现了……

二、 捕捉输出

以上的Example 4.是一种最简单的情况，你还可以在写入前对$content进行操作……
你可以设法捕捉一些关键字，然后去对它进行再处理，比如Example 3.所述的PHP语法高亮显示。个人认为，这个功能是此函数最大的精华所在，它可以解决各种各样的问题，但需要你有足够的想象力……
Example 5.

程序代码 程序代码

<?php
Function run_code($code) {
If($code) {
ob_start();
eval($code);
$contents = ob_get_contents();
ob_end_clean();
}else {
echo "错误！没有输出";
exit();
}
return $contents;
?>
}

以上这个例子的用途不是很大，不过很典型$code的本身就是一个含有变量的输出页面，而这个例子用eval把$code中的变量替换，然后对输出结果再进行输出捕捉，再一次的进行处理……

Example 6. 加快传输

程序代码 程序代码

<?
/*
** Title.........: PHP4 HTTP Compression Speeds up the Web
** Version.......: 1.20
** Author........: catoc <catoc@163.net>
** Filename......: gzdoc.php
** Last changed..: 18/10/2000
** Requirments...: PHP4 >= 4.0.1
** PHP was configured with --with-zlib[=DIR]
** Notes.........: Dynamic Content Acceleration compresses
** the data transmission data on the fly
** code by sun jin hu (catoc) <catoc@163.net>
** Most newer browsers since 1998/1999 have
** been equipped to support the HTTP 1.1
** standard known as \"content-encoding.\"
** Essentially the browser indicates to the
** server that it can accept \"content encoding\"
** and if the server is capable it will then
** compress the data and transmit it. The
** browser decompresses it and then renders
** the page.
**
** Modified by John Lim (jlim@natsoft.com.my)
** based on ideas by Sandy McArthur, Jr
** Usage........:
** No space before the beginning of the first \&#39;<?\&#39; tag.
** ------------Start of file----------
** |<?
** | include(\&#39;gzdoc.php\&#39;);
** |? >
** |<HTML>
** |... the page ...
** |</HTML>
** |<?
** | gzdocout();
** |? >
** -------------End of file-----------
*/
ob_start();
ob_implicit_flush(0);
function CheckCanGzip(){
global $HTTP_ACCEPT_ENCODING;
if (headers_sent() || connection_timeout() || connection_aborted()){
return 0;
}
if (strpos($HTTP_ACCEPT_ENCODING, \&#39;x-gzip\&#39;) !== false) return \"x-gzip\";
if (strpos($HTTP_ACCEPT_ENCODING,\&#39;gzip\&#39;) !== false) return \"gzip\";
return 0;
}
/* $level = compression level 0-9, 0=none, 9=max */
function GzDocOut($level=1,$debug=0){
$ENCODING = CheckCanGzip();
if ($ENCODING){
print \"n<!-- Use compress $ENCODING -->n\";
$Contents = ob_get_contents();
ob_end_clean();
if ($debug){
$s = \"<p>Not compress length: \".strlen($Contents);
$s .= \"
Compressed length: \".strlen(gzcompress($Contents,$level));
$Contents .= $s;
}
header(\"Content-Encoding: $ENCODING\");
print \"x1fx8bx08x00x00x00x00x00\";
$Size = strlen($Contents);
$Crc = crc32($Contents);
$Contents = gzcompress($Contents,$level);
$Contents = substr($Contents, 0, strlen($Contents) - 4);
print $Contents;
print pack(\&#39;V\&#39;,$Crc);
print pack(\&#39;V\&#39;,$Size);
exit;
}else{
ob_end_flush();
exit;
}
}
?>

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