In-depth analysis of Php output buffering cache and program cache_PHP tutorial

Test the ob cache and program cache below:
In order to make the test effect more obvious before testing, we first turn off the ob cache and set an obvious error level in php.ini.
Output_buffering=off
Display_errors=on
Code 1:

The code is as follows:

echo "php";
header("content-type:text/html;charset='utf-8'");
echo 'ok';

will appear
php
Warning: Cannot modify header information - headers already sent by (output started at D:wwwapachehtdocstestt2.php:2) in D:wwwapachehtdocstestt2.php on line 3
ok
Code 2:

The code is as follows:

ob_start();
 echo "php";
 header("content-type:text/html;charset='utf-8'");
 echo 'ok';

The result is completely correct

Cause analysis:
Code 1: Php has already sent a header information to the browser when echo 'php',
when it appears again
header("content-type: text/html;charset='utf-8'");
I saw another header information. At this time, the above header information had been typed back. I couldn't change it and an error occurred.
Code 2: The ob cache is turned on. When echoing 'php', the data to be sent to the browser is first placed in the ob cache. Then, when a header information is encountered, it is also placed in the Ob cache. , when the page ends, press the http protocol to cache the program and return it to the browser.
For a deeper understanding, look at the following code
Code 3:

The code is as follows:

ob_start();
echo "php";
header("content-type:text/html;charset='utf-8'");
echo 'ok';
echo '
';
$ob=ob_get_contents();
echo $ob;

Yes Output

Ob_get_contents() just gets the contents of the ob cache without knowing them
Ob_get_contents( ) must be used before the ob cache is cleared.
Code 4:

The code is as follows:

ob_start(); 
echo "php"; 
ob_clean();//清除缓存内容但不关闭缓存区，还能用(往里添加东西) 
header("content-type:text/html;charset='utf-8'"); 
echo 'ok'; 
echo '
'; 
$ob=ob_get_contents(); 
echo $ob;

Result:

Code 5:

The code is as follows:

ob_start();
echo "php";
ob_end_clean();//清空缓存内容并关闭缓存区，ob_get_contents取不到内容
header("content-type:text/html;charset='utf-8'");
echo 'ok';echo '
';
$ob=ob_get_contents();
echo $ob;

Result:

Code 6:

The code is as follows:

ob_start();
echo "php";
ob_end_flush();//把缓存送到程序缓存内并关闭ob缓存
header("content-type:text/html;charset='utf-8'");
echo 'ok';
echo '
';
$ob=ob_get_contents();
echo $ob;

Code 7: Compare code 6 with ob_flush()

The code is as follows:

ob_start();
echo "php";
ob_flush();//把Ob 缓存送到程序缓存，不关闭ob缓存
header("content-type:text/html;charset='utf-8'");
echo 'ok';
echo '
';
$ob=ob_get_contents();
echo $ob;

Result:

Ob_clean()
Clear the ob cache content but do not close it
Ob_get_flush()
Flush the cache to the program cache, Turn off ob cache
Code 8:

The code is as follows:

Ob_start();
echo 'abc';
header("content-type:text/html;charset='utf-8'");
echo 'hello';
Ob_flush();
echo 'aa';
echo ob_get_contents();
//abchelloaaaa

2.ob_flush(),flush( ) and program cache
Code 9:

The code is as follows:

ob_start();
echo 'a';
flush();//把Ob缓存冲刷到程序缓存再冲刷到浏览器输出，不影响ob缓存
echo ob_get_contents();
//aa

Code 10:

The code is as follows:

ob_start();
echo 'a';
ob_flush();//把Ob缓存冲刷到程序缓存,ob里没有了缓存内容
echo "ob_con".ob_get_contents();
//a     是按正常输出的，Ob里没内容

Program cache:
Code 11:

The code is as follows:

echo str_repeat(" ",1024);//一些版本的 Microsoft Internet Explorer 只有当接受到的256个字节以后才开始显示该页面，
所以必须发送一些额外的空格来让这些浏览器显示页面内容。 
for($i=0;$i<5;$i++){
echo $i;
echo "
";
sleep(1);
flush();
}

It will output one number per second
If there is no flush(); it will temporarily store all the output in the program cache, and then return it to the browser as a whole after it is completed. This example illustrates the program cache.

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