What you should know about the correct usage of require() file inclusion in PHP_PHP Tutorial

When I looked at some PHP framework source codes in the past, it was strange that dirname (__FILE__) was used to piece together the file path when the file was included. I didn’t know what the benefits of doing so were, but I finally discovered the reason.

Let’s look at a simple example:

There are three php files a, b, c. a.php is in the root directory of the website, b.php is in the b folder - b/b.php, and c.php is in the c folder - c/c.php. Some confusion? It’s clear when you look at the picture:

Both a.php and b.php include c.php, and finally c.php includes a php file in the d folder - d/d.php.

Let’s take a look at a.php first:

<span  1</span> <?<span php 
</span><span  2</span> 
<span  3</span>     <span $file_name</span> = 'a.php'<span ;
</span><span  4</span> 
<span  5</span>     <span echo</span> "this is a.php"<span ;
</span><span  6</span>     <span echo</span> "<hr>"<span ;
</span><span  7</span> 
<span  8</span>     <span require</span>('c/c.php'<span );
</span><span  9</span> 
<span 10</span>  ?>

This is a very simple code. After printing, it contains c/c.php. Next, we need to look at c/c.php:

<?<span php 
    </span><span $c_file_name</span> = 'c.php'<span ;

    </span><span echo</span> 'this is c.php, is required by ' . <span $file_name</span><span ;
    </span><span echo</span> "<hr>"<span ;

    </span><span require</span>('../d/d.php'<span );
 </span>?>

Print output "this is c.php, is required by a.php", $file_name is a variable defined in a.php. At the end, d.php is included. Because the d folder is one layer above the current c.php file, according to common sense, we will write the path as "../d/d.php" as a matter of course. But unfortunately, an error will be reported. The reason is that when you include other files in an included file such as c.php, the path is relative to the outermost parent file, that is, relative to a.php, which can be understood as because you are included by me. , so you have to rely on me. It seems very mysterious, but the principle is actually very simple: you can think of require('c/c.php'); as the code in the c/c.php file, so that our a.php can look like this:

<?<span php 
    </span><span $file_name</span> = 'a.php'<span ;

    </span><span echo</span> "this is a.php"<span ;
    </span><span echo</span> "<hr>"<span ;

    </span><span //</span><span  require('c/c.php');</span>
    <span $c_file_name</span> = 'c.php'<span ;

    </span><span echo</span> 'this is c.php, is required by ' . <span $file_name</span><span ;
    </span><span echo</span> "<hr>"<span ;

    </span><span require</span>('../d/d.php'<span );
 </span>?>

At this point, you can see that when we want to include the d/d.php file, is the path just now wrong? Because now we are in the a.php code, we are relative to the a.php file, of course, the path should be require('d/d.php'); We modify the code as follows:

<?<span php 
    </span><span $file_name</span> = 'a.php'<span ;

    </span><span echo</span> "this is a.php"<span ;
    </span><span echo</span> "<hr>"<span ;

    </span><span //</span><span  require('c/c.php');</span>
    <span $c_file_name</span> = 'c.php'<span ;

    </span><span echo</span> 'this is c.php, is required by ' . <span $file_name</span><span ;
    </span><span echo</span> "<hr>"<span ;

    </span><span require</span>('d/d.php'<span );
 </span>?>

At this point, you haven’t understood the meaning yet, so you need to look down. Let’s look at b/b.php:

<?<span php 
    </span><span $file_name</span> = 'b.php'<span ;

    </span><span echo</span> "this is b.php"<span ;
    </span><span echo</span> "<hr>"<span ;
    
    </span><span require</span>('../c/c.php'<span );
 </span>?>

No need to explain, there is no problem, but when you replace require('../c/c.php'); with the code in c/c.php, you will find the problem , note that we have just modified the code in c/c.php and changed require('../d/d.php'); to require('d/d.php'); See what is included below Code:

<?<span php 
    </span><span $file_name</span> = 'b.php'<span ;

    </span><span echo</span> "this is b.php"<span ;
    </span><span echo</span> "<hr>"<span ;
    
    </span><span //</span><span  require('../c/c.php');</span>
    <span $c_file_name</span> = 'c.php'<span ;

    </span><span echo</span> 'this is c.php, is required by ' . <span $file_name</span><span ;
    </span><span echo</span> "<hr>"<span ;

    </span><span require</span>('d/d.php'<span );
 </span>?>

So, compared to b/b.php, the path of require('d/d.php'); is wrong, it should be require('../d/d.php');. You go back and modify the require path in c/c.php, but it’s wrong. After you modify it, b/b.php can run normally, but a/a.php can’t. Is it true that they share c/c? .php, it affects the whole body, what should I do?

At this time, we return to the dirname(__FILE__) mentioned at the beginning of the article. This is a good thing and can completely solve the above problems. Using it, you don't need to worry about which file contains your file and which path it is under. You don't need to worry about the level of the parent file, because dirname(__FILE__) can specify the path relative to the current file. In other words, we need to change the require path in our c/c.php to:

<?<span php 
    </span><span $c_file_name</span> = 'c.php'<span ;

    </span><span echo</span> 'this is c.php, is required by ' . <span $file_name</span><span ;
    </span><span echo</span> "<hr>"<span ;

    </span><span require</span>(<span dirname</span>(<span __FILE__</span>) . '/../d/d.php'<span );
 </span>?>

Here, we only need to use c/c.php as a reference. Compared to it, d/d.php is at the upper level. In this way, there is only one standard, and that is, I shall prevail. Whether you include me or he includes me, I only use myself as the criterion, and the files I want to include are only relative to myself.

For fellow practitioners who don’t understand dirname(__FILE__), please google it, it’s very simple.

Okay, this ends the PHP technology sharing. If you have any questions or errors, please leave a message. By the way, this is my first standard technical blog post. The first article is hydrology, the second article is quasi-technical, and today I finally wrote a technical article, Ou Ye.