What keywords are used to define constants in php

In PHP, use the const keyword to define constants. Characteristics include: must use identifier naming rules, values ​​cannot be modified, cannot start with $, are globally accessible, and cannot be declared private or protected. Constants are used to store immutable values, such as mathematical constants, configuration settings, and enumeration values, to improve readability and maintainability.

Keywords for defining constants in PHP

In PHP, use the const key words to define constants.

Usage

Syntax:

<code class="php">const 常量名称 = 值;</code>

For example:

<code class="php">const PI = 3.14;</code>

Features

• The names of constants must follow the identifier naming rules.
• The value of a constant cannot be modified and cannot be changed once it is defined.
• Constant values ​​cannot begin with a dollar sign ($).
• Constants can be accessed globally without using the global keyword.
• Constant cannot be declared private or protected.

Usage scenarios

Constants are usually used to store immutable values, such as:

• Mathematical constants, such as PI, E.
• Configuration settings, such as website name and database connection string.
• Enumeration values, such as status codes and user roles.

By defining constants, you can improve the readability and maintainability of your code and avoid errors caused by hard-coded values.

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