Detailed explanation of PHP output buffer control

This article mainly introduces PHP output buffering control. Detailed relevant information and simple sample codes are provided here to help you learn and reference. Interested friends can refer to

PHP Buffering Introduction

In fact, my impression of the php ob series is still very vague. I don’t know much about how to play it. In my usual curd, I really don’t have an in-depth understanding of these contents. As a phper, I am very ashamed. After searching online and copying each other, the phenomenon described by the author cannot occur when running the code. This article is a conscientious product, and the code has been run by the author.

When executing output, such as echo, print. The output is not sent to the web server immediately, but the data is written to the php buffer. The benefits of the php output_buffering mechanism certainly improve performance. In fact, the php file is finally displayed on the browser and goes through three buffering stages: php buffer=》web server buffer=》browser buffer. Finally displayed in the browser

By default, php buffer is turned on, and the default value of the buffer is 4096, which is 4 kb. You can find the output_buffering configuration in the php.ini configuration file. Buffer is a memory address space. The default size of Linux system is generally 4096 (4kb), which is one memory page. It is mainly used to store data transfer areas between devices with unsynchronized speeds or devices with different priorities. Through the buffer, the processes can wait less for each other. Here is a more general example. When you open a text editor to edit a file, every time you enter a character, the operating system will not immediately write the character directly to the disk, but first write it to the buffer. When writing When a buffer is full, the data in the buffer will be written to the disk. Of course, when the kernel function flush() is called, it is mandatory to write the dirty data in the buffer back to the disk.

For example

<?php
echo "南无阿弥陀佛<br>";
header("content-type:text/html;charset=&#39;utf-8&#39;");
echo "真善忍好!";
//output
//南无阿弥陀佛
//真善忍好

##header()must be called before any actual output, but we The program has output but runs normally. Looking at the following code:

<?phpecho "南无阿弥陀佛<br>";
ob_flush();
header("content-type:text/html;charset=&#39;utf-8&#39;");
echo "真善忍好!";
//output
//南无阿弥陀佛
//Cannot modify header information - headers already sent by (output started at E:\php\test.php:3)
//真善忍好

The above program shows that the program does not output immediately, but only refreshes the buffer and outputs when the ob_flush function is called.

ob_flush() and flush()

ob_flush() and flush() functions are available in the PHP manual You can check it out for detailed instructions. The difference between the two is:

ob_flush() is to refresh PHP's own buffer

flush() is to refresh the WebServer server buffer. Output to browser. But the following situation will occur:

1. Individual web server programs, especially web server programs under Win32, will still cache the output of the script before sending the results to the browser. , until the end of the program.

2. Some Apache modules, such as mod_gzip, may cache their own output, which will cause the results generated by the flush() function to not be sent to the client browser immediately.

3. Even the browser will cache the received content before displaying it. For example, the Netscape browser caches content until it receives a line break or the beginning of an html tag, and does not display the entire table until it receives a tag.

4. Some versions of Microsoft Internet Explorer will only begin to display the page after receiving 256 bytes, so some extra spaces must be sent to allow these browsers to display the page content.

For example:

<?php
/**
Server:LightTPD/1.4.28 (Win32)
X-Powered-By:PHP/5.3.27
*/
echo &#39;佛法无边&#39;."<BR>";
ob_flush();
flush();
sleep(1);
echo &#39;法轮常转&#39;;

//output

The above code is output line by line on the chrome browser, and on the ie series The browser outputs all. In fact, it is the fourth item above. Some browsers only start displaying when they receive 256 characters. Change the above code to the following form:

<?php
/**
Server:LightTPD/1.4.28 (Win32)
X-Powered-By:PHP/5.3.27
*/
echo str_pad(&#39;&#39;,240)."\n"; 
echo &#39;佛法无边&#39;."<BR>";
ob_flush();
flush();
sleep(1);
echo &#39;法轮常转&#39;;

//output

This will be output line by line under IE because it exceeds 256 characters.

ob Other function descriptions

1.ob_end_flush and ob_end_clean

End ends as the name suggests, closing the buffer Areas, both turn off the output buffer, one is the output buffer, and the other is clear. For example,

<?php
/**
Server:LightTPD/1.4.28 (Win32)
X-Powered-By:PHP/5.3.27
*/
echo &#39;before&#39;;
ob_end_clean();
echo str_pad(&#39;&#39;,4096)."\n";
for ($i=10; $i>0; $i--) 
{ 
 echo $i;
 sleep(1);
}

The above code outputs all the contents at once, rather than outputting them one by one. Doesn't ob_end_clean() turn off the buffer? Why not output them one by one? In fact, as we said above, php is not output directly to the browser, but to the web server. Although php has no buffer. But the web server still exists. So the following code:

/**
Server:LightTPD/1.4.28 (Win32)
X-Powered-By:PHP/5.3.27
*/
echo 'before';
ob_end_clean();
echo str_pad('',4096)."\n";
for ($i=10; $i>0; $i--) 
{ 
 flush();
 echo $i;
 sleep(1);
}

plus flush() will output it line by line. If you replace ob_end_clean with ob_end_flush, before will be output.

For other functions, please refer to the manual, which is relatively simple.

Summary

From the php script to the browser, you need to go through php buffer=》web server buffer=》browser buffer. Finally displayed to the browser. Indispensable. So we need ob_flush and flush and add echo str_pad('',4096) to debug the effect you want.

Summary: The above is the entire content of this article, I hope it will be helpful to everyone's study.

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