Be careful about php require_once usage and relative directories

The article introduces the usage of require_once that everyone often encounters in PHP development. Friends in need can refer to it.

wwwroot //Website root directory. The absolute path is: F:/wwwroot

-- folder_a // Folder A

file_a_a.php

file_a_b.php

file_a_c.php

-- folder_b // Folder B

file_b_a.php

file_b_b.php

file_b_c.php

-- index.php

**************************************************** ******************

This directory hierarchy is already very clear:

wwwroot is the root directory, below which there is the index.php file and two folders folder_a and folder_b

These two folders each have 3 php files

Let’s first look at the contents of the index.php file:

The code is as follows

Copy code

代码如下

复制代码

require_once("folder_a/file_a_a.php");

echo "文件folder_a_a.php被包含成功";

require_once("folder_a/file_a_a.php");

代码如下

复制代码

require_once("../folder_b/file_b_a.php");

$x = new X();

$x.printInfo();

echo "The file folder_a_a.php was included successfully";

代码如下

复制代码

class X{

function printInfo(){

echo 'success;

}

?> Look at the contents of the folder_a/folder_a_a.php file:

The code is as follows	Copy code
<🎜> require_once("../folder_b/file_b_a.php");<🎜> <🎜> $x = new X();<🎜> <🎜> $x.printInfo();<🎜> <🎜>?>

Finally, let’s take a look at the contents of the folder_b/folder_b_a.php file:

The code is as follows	Copy code
<🎜> class X{<🎜> <🎜> function printInfo(){<🎜> <🎜> echo 'success;<🎜> <🎜> }<🎜> <🎜> }<🎜> <🎜>?>

ok if I run floder_a/file_a_a.php directly now

Then it will output: success

If I run index.php under wwwroot

Then an error will be reported because the included file cannot be found: file_b_a.php

But if I add dirname(__FILE__).'/'

to all require_once()

Then no matter you run file_a_a.php or index.php, the output will be normal

**************************************************** **********

Question:

The first time I used a relative path, so an error occurred when I included it repeatedly

The second time I used the absolute path, so there was no error. But I am still a little confused:

I first analyzed the following reasons why using relative paths will cause errors:

I run index.php, it can find the folder_a directory and file_a_a.php in that directory, so it copies the contents of folder_a/file_a_a.php to the first line of index.php (including the statement line), and then continue to run (that is, run the included content), so this is equivalent to running require_once('../folder_b/file_b_a.php'); in file_a_a.php in index.php. Find this path file (file_b_a.php) based on the current location of index.php, but of course it can’t be found, so it’s an error.

But isn’t it the same when I use absolute paths? But why doesn’t it go wrong? Maybe everyone is a little confused about this sentence, let me explain it in detail (according to the running order of the program).

The program first runs index.php (note that I added dirname(__FILE__) at this time, so the current path is absolute),

index.php first runs the first line of code: require_once(dirname(__FILE__).'/'.'folder_a/file_a_a.php');

dirname(__FILE__) is f:/wwwroot/, so the path contained in this code is:

f:/wwwroot/folder_a/file_a_a.php

This path is correct, so it’s no problem, right

ok the first step is completed correctly

Then it copies the code in file_a_a.php to this location in index.php:

Then it still continues to run: This is to run all the code in file_a_a.php in index.php, so let’s see what code it runs?

The code is as follows

Copy code

代码如下

复制代码

require_once(dirname(__FILE__).'/'."../folder_b/file_b_a.php");

$x = new X();

$x.printInfo();

require_once(dirname(__FILE__).'/'."../folder_b/file_b_a.php");

代码如下

复制代码

require_once(dirname(__FILE__).'/'."../folder_b/file_b_a.php");

$x = new X();

$x.printInfo();

echo "文件folder_a_a.php被包含成功";

$x = new X();

$x.printInfo();

代码如下

复制代码

c.php

require_once("a.php");
require_once("demo/b.php");
B::demo();a.php
class A
{
}

Yes, that’s it. It should be noted that these codes have been copied to index.php, that is to say, the content of index.php now actually becomes:

The code is as follows	Copy code
<🎜> require_once(dirname(__FILE__).'/'."../folder_b/file_b_a.php");<🎜> <🎜> $x = new X();<🎜> <🎜> $x.printInfo();<🎜> <🎜> echo "The file folder_a_a.php was included successfully";<🎜> <🎜>?>

Let’s take a look at some things to note Suppose there are the following three files, c.php a.php b.php and the corresponding storage directory is: localhost/ localhost/ localhost/demo

The code is as follows	Copy code
c.php require_once("a.php"); require_once("demo/b.php"); B::demo();a.php class A { }

The content of b.php is more interesting, because it inherits CLASS A, so I also introduced a.php into it

The code is as follows

代码如下	复制代码
require_once("../a.php"); class B extends A { public static function demo() { echo "xx"; } }

Copy code

require_once("../a.php");
class B extends A {

代码如下	复制代码
require_once("a.php"); require_once("../a.php"); class B extends A { public static function demo() { echo "xx"; } } B::demo();

Public static function demo()

{
echo "xx";

}

The system reports an error when executing localhost/c.php. The error message is as follows Warning: require_once(../a.php) [function.require-once]: failed to open stream: No such file or directory in F:wwwdemob.php on line 2

Fatal error: require_once() [function.require]: Failed opening required '../a.php' (include_path='.;C:php5pear') in F:wwwdemob.php on line 2 However, I was surprised to find that if Remove the require_once statement in b.php and the execution is normal. So there must be too many require_once statements defined? The reason is that Class A was redefined twice? But no. If I only add require_once(‘a.php’); to c.php, it will be correct even if I write it twice. So what’s going on?

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