Detailed explanation of ob function extension examples in php

For a new PHP programmer, the PHP buffer is almost transparent. In their minds, with an echo print_r function, the data will fly to the browser with a 'swish' sound and be displayed. I have always thought so simply. In fact, in the world of technology, things have always progressed from simplicity to complexity. Maybe those technology developers started out as simple as you and me, but in the face of the cruel reality, they had to adjust their strategies in order to improve the operating efficiency of the machine. Finally, they thought of those things that make the machine more efficient. An idea we admire.

When it comes to buffering, that is, buffer, we must compare it with cache. Simply comparing definitions is meaningless. Why not look at what they do. Caching solves the problem of how to quickly find and utilize data and save CPU consumption, while buffering solves the problem of mismatch between high-speed CPU and low-speed I/O devices.

Let’s talk about the other protagonist of this article, the ob function. ob is the abbreviation of output_buffering. Since the ob function is a PHP extension function, the main operation of the ob function is php buffer.

After briefly talking about the two protagonists of this article, we must return to the topic at the beginning. How does the data output by the echo print_r function reach the browser for the user to see? The actual process is like this:

echo、print_r=>php output_buffering=>webServer buffer=>browser buffer=>browser display

We can clearly see that from the echo and print_r functions to sending information to the client, it has gone through two buffers. Goes through a browser buffer. What we mainly discuss in this article is php output_buffering.

The usage of the buffer when the ob function is not used

Our codes often do not use the ob function at all, so do they use the buffer? This depends on the php settings. The buffer is controlled through the output_buffering variable in php.ini. Its default value is off and can be set to on to open the buffer. After calling the buffer, even if the ob function is not used in the program, the code actually uses the buffer. In addition, regardless of the setting of output_buffering in php.ini, php in cli mode is always closed by default.

Why is it a buffer? To put it simply, the high-speed CPU has processed its own data early and wants to transmit it to the user through the line, but the line is too narrow and cannot be transmitted at once. If a buffer is introduced, the CPU can quickly put the generated data into the buffer, and then rest somewhere cool. The buffer outputs data in a timely manner according to instructions. This effectively solves the contradiction between high-speed CPU and low-speed I/O devices.

When will the data in the buffer be output? 1. When the buffer is full, the buffer has a capacity, and the content will be automatically output when the limit is reached. 2. The script execution is completed. Many small programs don't output that much content. You can't wait until the buffer is full before outputting ~ This is natural.

　Buffer usage when using the ob function

ob_start()

Turn on the output buffer. This function is one of the functions we call most. With output_buffering set to on or x k, this function does not so much open the output buffer as it expands the output buffer to a large size. Of course, under the condition that output_buffering is set to off, ob_start will play the role of opening the buffer. ob_start() can also pass an optional parameter output_callback function, which is explained in detail in the official PHP manual.

ob_get_contents()

Just get the contents of the output buffer, but don't clear it.

ob_end_clean()与ob_clean()

The difference between these two functions can be seen literally. The former clears the buffer contents and closes it, while the latter only does the clearing work. It should be noted that after using these two functions, the previous functions such as echo and print_r will not output the content.

The author once tried to print out the contents of ob_get_contents() through print_r, and then called ob_clean() to clear the buffer, so as not to affect subsequent operations on the buffer. Repeatedly failed. If you think about it carefully, the content of print_r is written to the buffer again, and the ob_clean() operation is performed later, so naturally there will be no output. Calling the ob_flush() function before the ob_clean operation can achieve the desired effect.

ob_flush()与flush()

ob_flush() sends the contents of the buffer and discards the contents. Therefore, it is best to use ob_get_contents() to obtain the buffer content before this function. flush() flushes out the server-side buffer and sends it to the client. Therefore, from a process perspective, ob_flush() should be called first and then the flush function.

　　另外说明下再Apache buffer flush()的工作原理：在apache module的sapi下，flush会通过调用sapi_module()的flush成员函数指针，间接使用apache的api：：ap_rflush刷新apache的输出缓冲区。当然apache其他模块比如mod_gzip可能改变这个动作的结果，可能自己进行输出缓冲区，这将导致flush()函数产生的结果不会立即被送到客户端浏览器。

ob_get_clean()

　　如果你已经熟练掌握ob_get_contents()和ob_clean()，那这个函数就很简单了。因为它是前两者的结合体。它主要是得到当前缓冲区的内容并删除当前输出缓冲区。

　　ob函数还有很多，但大部分用法比较简单，理解较为容易。大家可以参照php手册 ，里面会有详细的解释。本文列出了笔者开始并不是很理解的一些函数，当然今后还会有新的问题出现，想到问题并且解决问题，生活的乐趣也许就在此处吧。

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