如何防止在包含的文件中两次包含相同的文件? [英] How can I prevent to include same file twice in an included file?

问题描述

在主index.php文件中，包括header.php.两个文件都必须插入session.php, database.php等才能运行.但是，当包含header.php时，有两个相同的 require/include文件，因此有两个相同的函数，即查询.这会在文件中引起一些问题.
这个问题的解决办法是什么?

In a main index.php file, header.php is included. Both files must insert session.php, database.php etc. to run. But when header.php is included, there are two same require/include files, so there are two same functions, queries. This cause some problems in the file.
What is the solution of this problem?

推荐答案

使用include_once代替include.

include_once语句在脚本执行期间包含并评估指定的文件.这是一种与include语句类似的行为，唯一的区别是如果文件中的代码已经被包含，则不会再次被包含.顾名思义，它将仅包含一次.

The include_once statement includes and evaluates the specified file during the execution of the script. This is a behavior similar to the include statement, with the only difference being that if the code from a file has already been included, it will not be included again. As the name suggests, it will be included just once.

http://php.net/manual/en/function.include-一次.php

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