Instructions for using the ob_start function in PHP

Use PHP’s ob_start();

Control your browser cache

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 give you a simple example to give you a general impression of Output Control:

Example 1.

Program code

Copy code The code is as follows:

ob_start(); // Open buffer
echo "Hellon"; //Output
header("location:index.php"); //Redirect the browser to index.php
ob_end_flush(); //Output all Content to browser
?>

Everyone who knows the header() function knows that this function will send a file header to the browser, but if you use this function before If there is any output (including empty output, such as spaces, carriage returns and line feeds), an error will be prompted. 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 send by"! But with ob_start, there will be no error message. 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. They will not be output until you use flush or ob_end_flush, so it will not Any file header output errors!

1. Introduction to related functions:

1. Flush: refresh the contents of the buffer and output.

Function format: flush()

Note: This function is frequently used and is very efficient.

2. ob_start: Open the output buffer

Function format: void ob_start(void)

Note: 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. 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: 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: void ob_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 off absolute refresh

Usage: void ob_implicit_flush ([int flag])

Note: 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. The default is to close the buffer. After turning on absolute output, each Script output is sent directly to the browser, no need to call flush()

2. In-depth understanding:

1. About 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 give an example with a very obvious operating effect to illustrate flush.

Example 2.

Program code

Copy code The code is as follows:

for($i = 1 ; $i <= 300; $i++ ) print(" ");
// This sentence is very critical. The structure of the cache makes its content only when it reaches a certain size before it can be output from the browser
/ / In other words, if the cache content does not reach a certain size, it will not be output before the program execution is completed. After
// testing, I found that the lower limit of this size is 256 characters long. This means that the content received by the cache in the future will
// be sent out continuously.
For($j = 1; $j <= 20; $j++) {
echo $j."
";
flush(); //This will add new items to cache The content is squeezed out and displayed on the browser
sleep(1); //Let the program "sleep" for a second, which will allow you to see the effect more clearly
}
?>

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

2. About ob series functions:

I would like to first quote an example from my good friend y10k:

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? 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 code

Copy code The code is as follows:

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 save the phpinfo information of different users. This may not have been possible 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 is, for example, the PHP syntax highlighting in the author's forum is related to this (PHP's default syntax highlighting function will directly Output, the result cannot be saved. If it is displayed every time it is called, it will be a waste of CPU. The author's forum retains the result displayed by the syntax highlighting function by controlling the buffer). If you are interested, you can take a look.

Maybe now you have a certain understanding of the function of ob_start(). The above example seems 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 in cache After being written, the command is automatically run, such as ob_start("ob_gzhandler"); and our most common approach is to use ob_get_contents() to get the contents of 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 execution is completed. Of course, if you are using ob_get_contents(), then you have to control the output method yourself.

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

1. Static template technology

Introduction: The so-called static template technology uses a certain method to enable users to get html pages generated by PHP on the client side. 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, and 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.

As 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.

Program code

Copy code The code is as follows:

ob_start();// Open the buffer
?>

All output of the php page

Copy the code The code is as follows:

$content = ob_get_contents();//Get all the content output by the php page
$fp = fopen("output00001.html", "w"); //Create a file, and open it, ready to write
fwrite($fp, $content); //Write all the contents of the php page to output00001.html, and then...
fclose($fp);
? >

In this way, the so-called static template 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 biggest essence of this function. It can solve a variety of problems, but it requires you to have enough imagination...

Example 5.

Program code

Copy code The code is as follows:

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 above example It is not very useful, but it is very typical that $code itself is an output page containing variables. In this example, eval is used to replace the variables in $code, and then the output results are output captured and processed again...

Example 6. Speed up transmission

Program code

Copy code The code is as follows:

/*
** Title..........: PHP4 HTTP Compression Speeds up the Web
** Version..........: 1.20
** Author..........: catoc < ;catoc@163.net>
** Filename...: gzdoc.php
** Last changed..: 18/10/2000
** Requirements...: 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)
** 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 '** ----------Start of file----------
** |* * | include('gzdoc.php');
** |? >
** |
** |... the page ...
** |
** |** | 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, 'x-gzip') !== false ) return "x-gzip";
if (strpos($HTTP_ACCEPT_ENCODING,'gzip') !== 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 "nn";
$Contents = ob_get_contents();
ob_end_clean();
if ($debug){
$s = "

Not compressed 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 $Contents;
print pack('V',$Crc);
print pack('V',$Size);
exit;
}else{
ob_end_flush();
exit;
}
}
?>

Instructions for using the ob_start function in PHP_PHP Tutorial