Summary of concepts about PHP constants

Use define() function in php to define a constant. The so-called constant refers to a quantity whose value does not change. This article collects several articles about PHP constants. I hope it will be helpful to everyone's understanding of PHP constants. Let's take a look.

1.Detailed explanation of the definition and usage examples of PHP constants

We can understand constants as quantities whose values ​​do not change. Once a constant is defined, it cannot be changed anywhere else in the program script.

How to define constants: Constants are composed of English letters, underscores, and numbers. However, one thing to note is that the first letter of our constants cannot start with a number.

In PHP we use the define() function to define constants. The syntax of the define() function is as follows

2.Detailed explanation of PHP predefined constant examples

We can use PHP's predefined constants to obtain information in PHP. For example, we can use it to obtain the operating system of the current computer, the currently used PHP version information, etc. Some predefined constants commonly used in PHP are as follows: __FILE__ Default constant, PHP program file name; __LINE__ Default constant, number of PHP program lines

3.The relationship and difference between php constants and variables

Let’s first look at the difference between the two from the definition of php constants and variables:Constant : In PHP we use the define() function to define constants. For details, see: Detailed explanation of the definition and usage examples of PHP constants. Variables: All variables in PHP start with $, followed by the name of the variable, and assign a value to the variable. From the definition of PHP constants and variables, we can get: There is no dollar sign ($) in front of the constant; Constant can only be defined with the define() function, and Cannot pass assignment statements;

4.Detailed explanation of magic constant examples in php

When explaining PHP constants, we know that PHP Most of the constants in are unchanged, but there are 8 predefined constants that will change as the location of the code where they are located changes. These 8 constants are called magic constants. These special constants are not case-sensitive. PHP's "magic constants" are in the following table

5.Detailed explanation of php class constant definitions and examples

In hp we can understand that the value does not change The quantity is called a constant. So, what is a class constant? In fact, class constants are also easy to understand. We can call the value that always remains unchanged in the class a constant, and this constant can be called a class constant. Be sure to remember that you do not need to use the "$" symbol when defining and using constants.

Class constants belong to the class itself, not to object instances, and cannot be accessed through object instances

* Cannot be modified with public, protected, private, static

* Subclasses can be repeated To write constants in the parent class, you can call the constants in the parent class through (parent::)

[Q&A Recommendation]

How does MySQL convert constants Splicing with variables?

#php class constants to determine whether they are defined? Class constants are not constants

【Recommended entries】

Constant

Class constant

Magic constant

[Related article recommendations]

The difference between const and define in php constants Usage examples

In-depth understanding of built-in constants in Python

Variables and constants in PHP mobile Internet development

The above is the detailed content of Summary of concepts about PHP constants. For more information, please follow other related articles on the PHP Chinese website!