PHP basic tutorial PHP page buffering mechanism

PHP has many mechanisms and functions, which are actually magicians. If they are used repeatedly, magical effects will appear even with simple applications. Band of Brothers PHP training

Here we will talk about the ob_start() function.

　 The ob_start() function is used to open the buffer. For example, if there is output before the header() function, including carriage returns, spaces, and line breaks, there will be an error of "Header had all ready send by". In this case, you can use ob_start() to open it first. The data block and echo() output of the buffer PHP code will enter the buffer and will not be output immediately. Of course, opening the buffer has many functions, just use your imagination. The following four points can be summarized:

　1. Used for header( before ();//Output all the content to the browser

　?>

　 2. The phpinfo() function can obtain client and server-side information, but to save client-side information, the buffer method is the best choice.

　ob_start(); //Open the buffer

　phpinfo(); //Use the phpinfo function

　$info=ob_get_contents(); //Get the contents of the buffer and assign it to $info

　$file=fopen( 'info.txt','w');//Open the file info.txt

　fwrite($file,$info); //Write information to info.txt

　fclose($file); //Close the file info.txt

　　?>

　 3. Static page technology

　 ob_start(); //Open the buffer

　 ?>

　 All output of the php page

$content =ob_get_contents();//Get All contents output by the php page

　$fp =fopen("output00001.html", "w"); //Create a file and open it, ready to write

　fwrite($fp, $content); //Put Write all the contents of the php page into output00001.html, and then...

　　fclose($fp);

　?>

　 4. Output code

　Function run_code($code) {

　If($code) {

　ob_start();

　eval($code);

　$contents =ob_get_contents();

　ob_end_clean();

　}else {

　echo "Error! No output";

　exit();

　　}

　 return $contents;

　}

　 The Output Control function allows you to freely control the output of data in the script. It is very useful, especially when you want to output the file header after the data has been output. The output control function does not affect the file header information sent using header() or setcookie(), only the data blocks similar to echo() and PHP code.

　Let’s take a simple example to give everyone a general impression of OutputControl:

　Example 1.

　CODE
　ob_start(); //Open the buffer

　echo ”Hellon”; / /Output

　header(”location:index.php”);//Redirect the browser to index.php

　ob_end_flush();//Output all content to the browser

　?>

　 All pairs of headers Anyone who knows the () 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, an error will be prompted . If we remove ob_start() in the first line and execute this program again, we will find that we get an error message: "Header hadall ready send by"! But with ob_start, there will be no error message because when the buffer is turned on area, the characters after echo will not be output to the browser, but will be retained on the server. They will not be output until you use flush or ob_end_flush, so there will not be any errors in file header output!

　 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 will be saved in the internal buffer district. 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: Returns the contents of the internal buffer.

　 Usage: stringob_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: intob_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: voidob_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: voidob_end_clean(void)

Note: This function will not output the contents of the internal buffer but delete it!

　7 , ob_implicit_flush: Turn on or turn off absolute flush

Usage method: void ob_implicit_flush([int flag])

Description: Anyone who has used Perl knows the meaning of $|=x. This string can open/close the buffer, and The ob_implicit_flush function is the same as that one. 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().

　　II. In-depth understanding:

　1. About the Flush function :

　This function has appeared in PHP3. It is a very efficient function. It has a very useful function of refreshing the browser's cache. Let's give an example with a very obvious operating effect to illustrate flush.

　Example 2 .

　　CODE
　for($i = 1; $i <= 300;$i++ ) print(" ");

　 // This sentence is very critical. The structure of the cache makes its content only It must reach a certain size to be output from the browser

　　 // In other words, if the cache content does not reach a certain size, it will not be output before the program is executed. After

　 // testing, I found that the lower limit of this size is 256 characters long. This means that the content received by the cache in the future will be sent out continuously.

　For($j = 1; $j <= 20;$j++) {

　echo $j.”

　“;

　flush(); //This will cause the new content in the cache to be squeezed Go out and display it on the browser

　 sleep(1); // Let the program "sleep" for a second, which will allow you to see the effect more clearly

　}

　?>

　 You can go to the specific effect Take a look here http://www.php2000.com/~uchinaboy/out.php

The latest PHP chat room of PHP2000 uses this technology. Unfortunately, the source code is not disclosed.

Note: If in the program Add ob_implicit_flush() to the first part to turn on absolute refresh, and you can no longer use flush() in the program. The advantage of this is: improve efficiency!

　　2. Regarding the ob series functions:

　I would like to quote my good friend y10k first An example of:

　Example 3.

　For example, you can use the setting information of the server and the client, but this information will be different depending on the client. What if you want to save the output of the phpinfo() function? Without buffering Before area control, it can be said that there was no way at all, but with buffer control, we can easily solve it:

　CODE
　ob_start(); //Open the buffer

　phpinfo(); // Use the phpinfo function

　$info=ob_get_contents(); //Get the contents of the buffer and assign it to $info

　$file=fopen('info.txt','w');//Open the file info.txt

　fwrite($file,$info); //Write information to info.txt

　fclose($file); //Close the file info.txt

　?>

　Using the above method, you can put different The user's phpinfo information is saved, which I'm afraid there was no way to do before! In fact, the above is a method of converting some "processes" into "functions"!

Some people may ask: "Is this it? Is there anything else? Purpose?" Of course there is. For example, the PHP syntax highlighting in the author's forum 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 has retained the results displayed by the syntax highlighting function by controlling the buffer). If you are interested, you can take a look at http://www.zphp.com/bbs/!

Maybe everyone is interested now Now that you have a certain understanding of the function of ob_start(), the above example may seem simple, but in fact you have mastered the key points of using ob_start().

　 <1>. Use ob_start to open the browser's cache. This ensures that the contents of the cache will not be output before you call flush(), ob_end_flush() (or the program is executed).

< 2>. Now you should know the advantages you have: you can use header, setcookie and session after any output content, which is a great feature of ob_start; you can also use the parameters of ob_start to be written in the cache After that, the command is automatically run, such as ob_start("ob_gzhandler "); and our most commonly used method is to use ob_get_contents() to get the contents in the cache, and then process it...

　　<3>. When the processing is completed, We can use various methods to output, flush(), ob_end_flush(), and automatic output after the program is executed. Of course, if you are using ob_get_contents(), then you have to control the output method yourself.

Come on, let’s see what we can do with the ob series functions...

1. Static template technology

Introduction: The so-called static template technology is to use some method to make what the user gets on the client side generated by PHP html page. If this html page will no longer be updated, then when another user browses this page again, the program will no longer call PHP and related databases. For some websites with a large amount of information, such as sina, 163, sohu. The benefits of technology like this are huge.

　There are two ways to achieve static output that I know of:

　 <1>. Implemented through a class called template.inc.php of phplib modified by y10k.

　<2>. Use the ob series function to implement.

　For the first method, because it is not the issue to be studied in this article, I will not go into details.

　Let’s now take a look at the specific implementation of the second method:

　Example 4.

　CODE
　ob_start();//Open the buffer

　?>

　All output of the php page

　　
　 $content =ob_get_contents();//Get all the content output by the php page

　 $fp =fopen("output00001.html", "w"); //Create a file and open it, Prepare to write

　fwrite($fp, $content); //Write all the contents of the php page to output00001.html, and then...

　fclose($fp);

　?>

　In this way, the so-called Static templates can be easily implemented...

　 2. Capture output

The above Example 4 is the simplest case. You can also operate on $content before writing...

You can Try to capture some keywords and then reprocess them, such as the PHP syntax highlighting described in Example 3. Personally, I think this function is the best part of this function. It can solve a variety of problems, but it requires you to have enough imagination...

　Example 5.

　CODE
　Function run_code($code ) {

　If($code) {

　　ob_start();

　eval($code);

　$contents =ob_get_contents();

　ob_end_clean(); echo "Error! No output";

　exit();

　}

　 return $contents;

　}

　 The above example is not very useful, but it is typical that $code itself is an output page containing variables, and this The example uses eval to replace the variables in $code, and then captures the output and processes it again...

　Example 6. Speed ​​up the transmission

　CODE
　ob_start();

　ob_implicit_flush(0 );

Function CheckCanGzip(){

global$HTTP_ACCEPT_ENCODING;
　if(strpos($HTTP_ACCEPT_ENCODING , 'x-gzip') !== false) return ”x-gzip";

　if(strpos($HTTP_ACCEPT_ENCODING,'gzip') !== false) return ”gzip";

　return 0;

　　}

　　functionGzDocOut($level=1,$debug=0){

　 $ENCODING = CheckCanGzip();

　 if ($ENCODING){

　 print ”nn”;

　 $Contents =ob_get_contents();

　 ob_end_clean();

　 if ($debug){

　 $s = ”

Notcompress length: ”.strlen($Contents);

　 $s .= ”

　Compressed length:”.strlen(gzcompress($Contents,$level));

　$Contents .= $s;

　　}

　header(“Content-Encoding:$ENCODING”); ×00x00×00x00×00”;

$Size = strlen($Contents);

　$Crc = crc32($Contents);

　$Contents =gzcompress($Contents,$level);

　$Contents = substr($Contents,0, strlen($Contents ) – 4);

　print $Contents;

　print pack('V',$Crc);

　print pack('V',$Size);

　exit;

　}else{

　ob_end_flush( ; Compression has been carried out, and tests have shown that it will have an effect on pages above 10k, and the larger the page, the more obvious the effect...