PHP constants and variables use constants to restrict users from skipping certain files

长——Chinese literally means: long-lasting, unchanged for a long time.

Constant is easy to translate: a long-lasting value.

[Key knowledge] We define the knowledge level as: silent level

The scope of use of constants is very wide. We will use constants in the future to define our working directory, define some characteristics of account passwords, version numbers, etc. So this piece of knowledge is very important.

The definition and writing method of constants in the code:

define (constant name, constant value)

Note:

1. The constant value can only be the scalar we talked about in the previous chapter.

2. Constant names can be lowercase, but usually uppercase

3. Constant names can be without quotation marks, but usually with quotation marks.

4. When calling a constant in a string, it must be outside the quotation marks

5. It is recommended that only letters and underscores be used for constant names

Let’s experiment with code:

1. Try defining and calling a constant once

<?php

define('MY_NAME','PHP中文网');

echo MY_NAME;
//下面是错误的调用方式
echo '我的名字是MY_NAME';
//正确的调用方式该这么写
echo '我的名字是' . MY_NAME;
?>

2. Pay attention to project experiments

<?php
//其实可以小写，但是不好区分，所以我们规定通常大写
define('xiaoxie',true);
echo xiaoxie;

//常量可以在外面不加引号
define(YH,'不要对未来迷茫，迷茫的时候静下心来coding');
echo YH;

//只能用标量，我在后面用了一个数组，大家学一下就行,会报错的哟
define('BIAO',array(1,2,3));

?>

In addition, the system has also prepared some built-in constants for us. These constants are specified. Let’s get familiar with a few first. There are more system constants that we have studied in the previous volume. After getting started, we will slowly add and learn them.

The current lineThe path of the current file on the serverCurrent function nameCurrent class nameCurrent member method namePHP_OSThe operating system that PHP runs onPHP_VERSIONCurrent PHP versionTrait name ,php5.4 new additionThe directory where the file is locatedThe name of the current namespace (case sensitive)

defined() function is used as a security mechanism

You don’t need to master the knowledge here. After learning the function, you can look at this part of the code again.

defined() Let’s learn this usage, mainly to prevent others from bypassing the security check file.

Function: defined (constant)
Function: Pass the constant after the brackets of the function. If the constant is defined, it returns true, otherwise it returns false

[Scenario Simulation] Assume, we This set of online e-mall software requires payment. Checking whether the payment is made is done by checking the software authorization. The file version.php has the function of checking authorization. We have stipulated in the software that there is no authorization to check the file version. PHP cannot use this software. All code includes version.php. And in order to prevent someone from piracy, I can also encrypt the version.php code.

We have two files:

1. There is a version number, version statement and authorization statement in the middle of one file. The file name is version.php

2. A file has specific business functions. For example: user registration, login, etc., the file name is users.php

What should we do? ——That is to say, if the version.php file is not included, the code after users.php will be executed.

Let’s conduct an experiment:
version.php file

<?php

//此处是检查是否是否授权的业务部份代码xxxx
define('AUTH',true);

//略过模拟代码xxx行

?>

users.php

<?php
//尝试将include 'version.php'这一行代码注释后再执行看看，对比结果
include 'version.php';

if(!defined('AUTH')){
   echo '非法！非法！你尝试跳过授权文件';
   exit;
}


//模拟后面用户注册和用户登陆的代码xxx行
echo '用户注册';
?>

The experimental results show that version.php must be included, otherwise it will not be displayed The following echo 'User registration';

---

include
pronunciation: [ɪnˈklud]
explanation: contains

version
pronunciation: [ˈvɜ:ʃn]
Explanation: Version

user
Pronunciation: [ˈjuzɚ]
Explanation: Users
Plural: users

define
Pronunciation: [dɪˈfaɪn]
Explanation: Specifies

Function: include('Input file path and file name')
Function: The function of this function is to pass in the file with the specified path and let PHP include it for execution
Note: In the following chapters, we will specifically explain and experiment with include

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Constant name	Description
##LINE
FILE
FUNCTIOIN
CLASS
METHOD
TRAIT
DIR
NAMESPACE