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

2. Pay attention to project experiments

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.

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

users.php

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

Continuing Learning The current line The path of the current file on the server Current function name Current class name Current member method name PHP_OS The operating system that PHP runs on PHP_VERSION Current PHP version Trait name ,php5.4 new addition The directory where the file is located The name of the current namespace (case sensitive)

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