PHP's Ob_start () function usage

Classic Reference Fragments:

<?phpob_start (); Echo ' 123 '; Echo ' 456 '; Echo ' 789 '; $content = Ob_get_contents (); Ob_end_clean (); Echo $content;? >

The PHP manual says:

The output buffers are stackable, which means that when a ob_start () is active, you can call another Ob_start (). Just make sure that the correct number of Ob_end_flush () is correctly called. If multiple output callback functions are active, the output will be filtered sequentially through them in nested order.

Test Case:

<?phpinclude ' public/write.php '; Ob_start (); Ob_implicit_flush (0); Echo ' 123 '; $content = ob_get_contents (); Write ($ content);//ob_end_clean (); Ob_start (); Echo ' 456 '; $content = ob_get_contents (); write ($content); Ob_end_clean (); >

PHP Ob_start () usage

Use PHP's Ob_start () to control your browser cache.

The output control function gives you the freedom to control the outputs of the data in your script. It is very useful, especially when you want to output a file header after the data has been output. The output control function does not affect the header information sent using header () or Setcookie (), only data blocks that resemble Echo () and PHP code are useful.

Let's start with a simple example that gives you a general impression of the output control:

Example 1.

<?phpob_start (); Open buffer echo "Hellon"; Output header ("Location:"); redirect the browser to Ob_end_flush (); Output all content to browser?>

All people who know about the header () function know that this function sends a file header to the browser, but if there are any outputs (including null output, such as spaces, carriage returns, and line feeds) before using this function, an error is indicated. If we get rid of the first line of Ob_start () and execute the program, we'll find an error message: "Header had all ready to send by"! But with Ob_start, there is no hint of error, because when the buffer is opened, the character behind the echo is not output to the browser, but remains on the server until you use flush or ob_end_flush to output, so there will be no file header output error!

Introduction of related functions:

1,flush: Flush the contents of the buffer, output.

function format: Flush ()

Description: This function is often used and is highly efficient.

2.ob_start : Open Output buffer

function format: void Ob_start (void)

Note: When the buffer is active, all non-file header information from the PHP program is not sent, but is saved in the internal buffer. In order to output the contents of the buffer, you can use the contents of the Ob_end_flush () or flush () output buffers.

3.ob_get_contents : Returns the contents of the internal buffer.

How to use: String ob_get_contents (void)

Description: This function returns the contents of the current buffer and returns FALSE if the output buffer is not activated.

4.Ob_get_length: Returns the length of the internal buffer.

How to use: int ob_get_length (void)

Note: This function returns the length of the current buffer, as with ob_get_contents, if the output buffer is not activated. FALSE is returned.

5.Ob_end_flush : Sends the contents of the internal buffer to the browser, and closes the output buffer.

How to use: 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

How to use: void Ob_end_clean (void)

Description: This function does not output the contents of the internal buffer but deletes it!

7.Ob_implicit_flush: Turn absolute refresh on or off (implicitly refresh)

How to use: void Ob_implicit_flush ([int flag])

Description: People who have used Perl know the meaning of $|=x, this string can open/close the buffer, and the Ob_implicit_flush function is the same, the default is to close the buffer, open the absolute output, each script output is sent directly to the browser, no longer need to call flush ()

8.Ob_get_clean: Gets the contents of the current buffer and deletes the current output slow.

Essentially, ob_get_contents () and Ob_end_clean () are executed together.

Second, in-depth understanding:

1. About the Flush function:

This function appears in PHP3, is a very efficient function, he has a very useful function is to refresh the browser cache. Let's give a very obvious example of how flush works.

Example 2.

<?phpfor ($i = 1; $i <=; $i + +) {print ("");} This sentence is very key, the structure of the cache so that its content only to reach a certain size to output from the browser//In other words, if the cache content does not reach a certain size, it will not be output before the program is finished executing. After//test, I found that the limit of this size is 256 characters. This means that the content received by the cache will be sent//continuously. for ($j = 1; $j <=, $j + +) {echo $j. "<br/>"; flush (); This step causes the cache additions to be extruded to show the browser sleep (1); Let the program "Sleep" a second, will let you see the effect more clearly}?>

Note: If you open an absolute refresh by adding Ob_implicit_flush () to the program's header , you can no longer use flush () in your program, and the benefit is: increase efficiency!

that is, even if the Ob_start () function is not added, the page output is cached, and when the cache reaches a certain size and then output, and the Ob_start () function is added, all outputs are cached and only output when the active output (flush) (or program execution) is completed.

2. About OB series functions:

I'd like to cite an example of my good friend y10k first:

Example 3.

For example, you use the server and client settings information, but this information is different from the client, if you want to save the Phpinfo () function output what to do? Before there is no buffer control, it can be said that there is no way, but with the control of the buffer, we can easily solve:

<?phpob_start (); Open buffer phpinfo (); Use the Phpinfo function $info = ob_get_contents (); The contents of the buffer area are obtained and assigned to $info$file = fopen (' D:/cache.txt ', ' W '); Open File Fwrite ($file, $info); Write information to fclose ($file); Close File?>

Using the above method, you can save the Phpinfo information of different users, which in the past I am afraid there is no way to do! In fact, the above is a few "process" into the "function" Method! One might ask, "is that what it looks like?" Is there any other use? "Of course, such as the author of the Forum's PHP syntax highlighting is related to this (php default syntax highlighting function will be directly output, can not save the results, if every call is likely to be a waste of CPU, the author's forum to the syntax highlighting function display results with the method of control buffer), If you are interested, you can take a look.

Perhaps now you have a certain understanding of the function of Ob_start (), the above example seems simple, but actually has mastered the use of Ob_start () points.

<1>: Use ob_start to open the browser cache, which ensures that the contents of the cache are in your call flush (),Ob_end_flush () (or the program is finished) will not be output until it is executed.

<2> Now you should know the advantages you have: You can use the Header,setcookie and session after any output, which is a great feature of Ob_start, or you can use the Ob_start parameters after the cache is written , and then run the command automatically, such as Ob_start ("Ob_gzhandler"), and our most common practice is to use ob_get_contents () to get the contents of the cache before processing.

<3> When processing is complete, we can use various methods to output,flush (),Ob_end_flush (), and wait until the program finishes executing the automatic output. Of course, if you use ob_get_contents (), then you have to control the output mode.

Here, let's see what we can do with OB series functions:

First, static template technology

Introduction: The so-called static template technology is in some way, so that users on the client side is generated by PHP HTML page. If this HTML page is not updated again, then when another user browses to the page again, the program will no longer invoke PHP and the associated database, for some of the more informative sites, such as Sina,163,sohu. The benefits of a technology like this are enormous.

There are two ways I know to implement static output:

<1> A class implementation that modifies Phplib by y10k.

<2> Use the OB series function implementation.

For the first method, because it is not the issue to be studied in this article, so don't repeat it.

Let's take a look at the concrete implementation of the second approach:

Example 4.

<?phpob_start (); Open Buffer?>

Full output of PHP page

< $content = Ob_get_contents (); Get the full contents of the PHP page output $fp = fopen ("d:/index.html", "w"); Create a file and open, ready to write Fwrite ($fp, $content); Write all the contents of the PHP page, and then ... fclose ($FP);? >

In this way, the so-called static template is easily implemented ...

Second, capture the output

The above example 4 is one of the simplest cases where you can also manipulate the $content before writing.

You can try to catch some keywords and then go back to it, such as Example 3. The PHP syntax is highlighted. Personally, this function is the biggest essence of this function, it can solve a variety of problems, but need you have enough imagination.

Example 5.

<?phpfunction 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 use of this example is not very large, but the typical $code itself is a variable output page, and this example uses eval to replace the variables in the $code, and then the output to capture the output, and then once again processed.

Example 6. Faster transfer

<?/** * * Title ...: PHP4 HTTP Compression Speeds up the Web * * Version .....: * * Author ...: Catoc, <[email.  protected]> * * Filename ...: * * Last changed: 18/10/2000 * * requirments ...: PHP4 >= 4.0.1 * * PHP was confi Gured with--with-zlib[=dir] * * Notes ...: Dynamic Content Acceleration Compresses * * The data transmission data on T He fly * * Code by Sun Jin Hu (CATOC) <[email protected]> * * Most newer browsers since 1998/1999 has * * been EQ Uipped to support the HTTP 1.1 * * Standard known as "content-encoding." * * Essentially the browser indicates to the * * ser Ver that it can accept "content encoding" * * and if the server is capable it would then * * compress the data and transmit I T. The * * Browser decompresses it and then renders * * the page. * * * * Modified by John Lim ([email protected]) * * Based on ideas by Sandy McArthur, Jr * * Usage ...: * * No space Before the beginning of the first ' <? ' tag. * *------------Start of file----------* * |<? ** | Include ('); ** |? > * * |
 Ob_start () function usage for PHP