PHP需要/包含文件(PHP require/include file)

 我有以下程序结构： 
 
Root directory：-----index.php
                       |-------TPL directory
                                 |-------------header.php
                                 |-------------index.php
                                 |-------------footer.php
php file loading structure:

Root directory:index.php ----require/include--->tpl:index.php
                                                      |----require/include-->header.php
                                                      |----require/include-->footer.php
 
 root index.php： 
 
    <?php
function get_header(){
    require('./tpl/header.php');
}

function get_footer(){
    require('./tpl/footer.php');
}

$a = "I am a variable";
 
 要求（ './ TPL / index.php的'）; 
 
 TPL：index.php文件： 
 
    <?php
get_header();//when I change require('./tpl/header.php'); variable $a can work!!
echo '<br />';
echo 'I am tpl index.php';
echo $a;
echo '<br />';
get_footer();//when I change require('./tpl/footer.php'); variable $a can work!!
 
 TPL：header.php文件： 
 
    <?php
echo 'I am header.php';
echo $a;//can not echo $a variable
echo '<br/>';
 
 TPL：footer.php： 
 
    <?php
echo '<br />';
echo $a;//can not echo $a variable
echo 'I am footer';
 
 出于某种原因，当我使用函数来要求header.php和footer.php时，我的变量$ a没有得到回应。 如果我自己使用header.php或footer.php，它工作正常。 我不明白问题是什么。 您认为这里的问题是什么？ 

I have the following program Structure:
 
Root directory：-----index.php
                       |-------TPL directory
                                 |-------------header.php
                                 |-------------index.php
                                 |-------------footer.php
php file loading structure:

Root directory:index.php ----require/include--->tpl:index.php
                                                      |----require/include-->header.php
                                                      |----require/include-->footer.php
 
Root index.php :
 
    <?php
function get_header(){
    require('./tpl/header.php');
}

function get_footer(){
    require('./tpl/footer.php');
}

$a = "I am a variable";
 
require('./tpl/index.php');
 
TPL:index.php:
 
    <?php
get_header();//when I change require('./tpl/header.php'); variable $a can work!!
echo '<br />';
echo 'I am tpl index.php';
echo $a;
echo '<br />';
get_footer();//when I change require('./tpl/footer.php'); variable $a can work!!
 
TPL:header.php:
 
    <?php
echo 'I am header.php';
echo $a;//can not echo $a variable
echo '<br/>';
 
TPL:footer.php:
 
    <?php
echo '<br />';
echo $a;//can not echo $a variable
echo 'I am footer';
 
For some reason when I used function to require header.php and footer.php my variable $a doesn't get echoed. It works fine if I use header.php or footer.php on its own. I do not understand what the problem is. What do you think is the issue here?

原文：https://stackoverflow.com/questions/16883839