php ob_start(), ob_end_flush and ob_end_clean() multi-level buffering_PHP tutorial

ob_start() and ob_end_flush() are a good pair to control the output. There is no problem in understanding when they appear as a pair, but when they appear more often, it becomes more difficult to understand.

view sourceprint?01

02 ob_start();

03 echo 'level 1
';

04 ob_start();

05 echo 'level 2
';

06 ob_start();

07 echo 'level 3
';

08 ob_end_flush();

09 ob_end_flush();

10 ob_end_flush();

Obviously, the result is:

level 1
level 2
level 3

When the program is modified and ob_end_flush() is changed to ob_end_clean() to become the following, what do you think the result will be? Attached are the explanations of these functions:

ob_clean — Clear (erase) the output buffer
ob_end_clean — Clear (erase) the buffer and close output buffering
ob_end_flush — flush out (send out) the contents of the output buffer and close the buffer
ob_flush — Flush (send) the contents of the output buffer
ob_start — Open the output control buffer

view sourceprint?01

02 ob_start();

03 echo 'level 1
';

04 ob_start();

05 echo 'level 2
';

06 ob_start();

07 echo 'level 3
';

08 ob_end_clean();//Modifications

09 ob_end_flush();

10 ob_end_flush();

Result:

level 1
level 2

Maybe you think that ob_end_clean() will clear the output of its latest ob_start(); in fact, this statement is not very comprehensive. See the example below

view sourceprint?01

02 ob_start();

03 echo 'level 1
';

04 ob_start();

05 echo 'level 2
';

06 ob_start();

07 echo 'level 3
';

08 ob_end_clean(); //First modification

09 ob_end_flush();

10 ob_end_clean(); //Second modification

This time, nothing is output.

Isn’t there an ob_flush() in the middle? Logically speaking, it should output level2.

In fact, the main reason for this is the multi-level buffering mechanism of the output. This program example has three ob_start(), which means that it has three buffers A, B, and C. In fact, the php program itself also has a final output buffer, we will call it F.

In this program, these buffers have certain levels, C->B->A->F, F is the highest level and is the final output buffer of the program. We follow the above program. Give an explanation.

Just started. F:null

view sourceprint?1 ob_start();

Create a new buffer A. A: null -> F: null

view sourceprint?1 echo 'level 1
';

The program has output, and the output enters the lowest buffer A A: 'level 1
' -> F:null

view sourceprint?1 ob_start();

Create a new buffer B. B:null -> A: 'level 1
' -> F:null

view sourceprint?1 echo 'level 2
';

The program has output, and the output enters the lowest buffer B B:'level 2
' -> A: 'level 1
' ->F:null

view sourceprint?1 ob_start();

Create a new buffer C C:null B:'level 2
' A: 'level 1
' -> F:null

view sourceprint?1 echo 'level 3
';

The program has output, and the output enters the lowest buffer C C:'level 3
' -> B:'level 2
' -> A: 'level 1
' -> F:null

view sourceprint?1 ob_end_clean(); //First modification

Buffer C is emptied and closed. B:'level 2
' -> A: 'level 1
' -> F:null

view sourceprint?1 ob_end_flush();

Buffer B is output to the previous level buffer A and closed. A: 'level 1
level 2
' -> F:null

view sourceprint?1 ob_end_clean(); //Second modification www.2cto.com

Buffer A is cleared and closed. At this time, the contents of buffer A have not been actually output to the final F, so the entire program does not have any output.

ob There are many other functions, but as long as you can understand these mechanisms, it should not be difficult to understand. Attach the remaining functions

flush — Flush the output buffer
ob_clean — Clear (erase) the output buffer
ob_end_clean — Clear (erase) the buffer and close output buffering
ob_end_flush — flush out (send out) the contents of the output buffer and close the buffer
ob_flush — Flush (send) the contents of the output buffer
ob_get_clean — Get the contents of the current buffer and delete the current output buffer.
ob_get_contents — Returns the contents of the output buffer
ob_get_flush — Flushes (sends out) the contents of a buffer, returns the contents as a string, and closes the output buffer.
ob_get_length — Returns the length of the output buffer contents
ob_get_level — Returns the nesting level of the output buffering mechanism
ob_get_status — Get the status of all output buffers
ob_gzhandler — The callback function used in ob_start to compress the contents of the output buffer. ob_start callback function to gzip output buffer
ob_implicit_flush — Turn on/off absolute flushing
ob_list_handlers — List all output handlers in use.
ob_start — Open the output control buffer
output_add_rewrite_var — Add URL rewriter values ​​
output_reset_rewrite_vars — Reset URL rewriter values ​​

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