php: Detailed explanation of include file variable scope

This article summarizes the scope of several situations when include files in PHP. It is very simple and practical. I hope it will be helpful for everyone to become familiar with the use of include.

In php we sometimes need to include a file. For example, when I was writing a framework some time ago, I planned to use native PHP as the template, and then write a display method to introduce the template file, but this is just my imagination. .

After finishing writing, I found that all variables in the template were prompted to be undefined. Through various research and searching for information, I summarized the scope in several situations when including files.

The first situation: A file includes B file, and the variables in A can be called in B file.

A file code:

<?php
 $aaa = &#39;123&#39;;
 
 include "B.php";

B file code:

<?php

echo $aaa;

The content can be output normally.

Second case: A file includes B file, and then the variables of B file can be called in A file.
A file code:

<?php

include "B.php";

echo $fff;

B file code:

<?php

$fff = &#39;i am f&#39;;

At this time, the content can be output normally.

The third situation: Call B file in a method of a certain class in A file, and then the variables in the method can be called in B file.
A file code:

<?php

class test{
  public function show(){
    $bbb = &#39;abc&#39;;
    include "B.php";
  }
}

$t = new test;
$t->show();

B file code:

<?php

echo $bbb;

At this time, the content can be output normally.

Fourth case: A file imports B file through a defined function. Variables in A cannot be used in B file, but A file can be used. Variables in the calling function (display).
A file code:

<?php
$aaa = &#39;123&#39;;

function display($file){
  $bbb= &#39;asdasdas&#39;;
  include $file;
}

display("B.php");

B file code:

<?php
echo $aaa;
echo $bbb;

After running, $aaa prompts that it is undefined, and $bbb can be output normally.

So I started to assume that it was not feasible to introduce the template using a display method. Based on the three situations, I finally chose to write a class to import the template file. Currently, ThinkPHP and Smarty also use classes to introduce template files. Any deficiencies in the article are welcome to be corrected.

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