The difference between Define and Const in PHP
This article mainly introduces the difference between Define and Const in PHP. It has a certain reference value. Now I share it with you. Friends in need can refer to it.
We often change values that do not change frequently. Defined as a constant, constants are generally expressed in all capital letters without a dollar sign in front. So what is the difference between define and const?
A constant is a simple identifier. This value cannot be changed during script execution (except for so-called magic constants, which are not constants). Constants are case-sensitive by default. Normally constant identifiers are always uppercase.
You can use the define() function to define constants. After php5.3.0, you can use the const keyword to define constants outside the class definition. In php7, you can define array constants. In previous versions, the const keyword can only be used in classes. Once a constant is defined, it cannot be changed or undefined.
<?php
// 以下代码在 PHP 5.3.0 后可以正常工作
const USERNAME = '周伯通';
echo USERNAME.PHP_EOL;
echo constant("USERNAME");
const ZHOUUSERNAME = '周伯通九阴真经';define('MYUSERNAME','周伯通九阴真经2');
echo "<pre class="brush:php;toolbar:false">";
print_r(get_defined_constants());
?>The differences between constants and variables are as follows:
1. const is a language structure; define is a function, which can Specify whether to be case sensitive through the third parameter. true means case insensitivity, the default is false
2. const is simple and easy to read, and it is much faster to compile than define.
3. Const can be used in classes and is used to define class member constants. It cannot be modified after definition; define cannot be used in classes and can be used for global variables
<?php
class MyClass
{ const USER = '周伯通';
function showConstant() {
echo self::USER . PHP_EOL;
echo constant('USER'); // 注意：Warning: constant(): Couldn't find constant USER
}
}
$class = new MyClass();
$class->showConstant();4. const is defined at compile time, so it must be in the topmost scope and cannot be used in functions, loops and if conditions; while define It is a function, that is, it can be used wherever a function can be called.
<?php
$x = true;
if ($x==1){
//const FOO = 'BAR';
// 无效的invalid
}
if ($x==1){
define('FOO', 'BAR'); // 有效的valid
echo FOO;
}The above is the entire content of this article. I hope it will be helpful to everyone's learning. , please pay attention to the PHP Chinese website for more related content!
Related recommendations:
ob_start usage analysis in PHP
Explanation of PHP empty() function
The above is the detailed content of The difference between Define and Const in PHP. For more information, please follow other related articles on the PHP Chinese website!
Hot AI Tools
Undresser.AI Undress
AI-powered app for creating realistic nude photos
AI Clothes Remover
Online AI tool for removing clothes from photos.
Undress AI Tool
Undress images for free
Clothoff.io
AI clothes remover
Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!
Hot Article
Hot Tools
Notepad++7.3.1
Easy-to-use and free code editor
SublimeText3 Chinese version
Chinese version, very easy to use
Zend Studio 13.0.1
Powerful PHP integrated development environment
Dreamweaver CS6
Visual web development tools
SublimeText3 Mac version
God-level code editing software (SublimeText3)
Hot Topics
What are the basic requirements for c language functions
Apr 03, 2025 pm 10:06 PM
C language functions are the basis for code modularization and program building. They consist of declarations (function headers) and definitions (function bodies). C language uses values to pass parameters by default, but external variables can also be modified using address pass. Functions can have or have no return value, and the return value type must be consistent with the declaration. Function naming should be clear and easy to understand, using camel or underscore nomenclature. Follow the single responsibility principle and keep the function simplicity to improve maintainability and readability.
How to set password protection for export PDF on PS
Apr 06, 2025 pm 04:45 PM
Export password-protected PDF in Photoshop: Open the image file. Click "File"> "Export"> "Export as PDF". Set the "Security" option and enter the same password twice. Click "Export" to generate a PDF file.
The difference between H5 and mini-programs and APPs
Apr 06, 2025 am 10:42 AM
H5. The main difference between mini programs and APP is: technical architecture: H5 is based on web technology, and mini programs and APP are independent applications. Experience and functions: H5 is light and easy to use, with limited functions; mini programs are lightweight and have good interactiveness; APPs are powerful and have smooth experience. Compatibility: H5 is cross-platform compatible, applets and APPs are restricted by the platform. Development cost: H5 has low development cost, medium mini programs, and highest APP. Applicable scenarios: H5 is suitable for information display, applets are suitable for lightweight applications, and APPs are suitable for complex functions.
Concept of c language function
Apr 03, 2025 pm 10:09 PM
C language functions are reusable code blocks. They receive input, perform operations, and return results, which modularly improves reusability and reduces complexity. The internal mechanism of the function includes parameter passing, function execution, and return values. The entire process involves optimization such as function inline. A good function is written following the principle of single responsibility, small number of parameters, naming specifications, and error handling. Pointers combined with functions can achieve more powerful functions, such as modifying external variable values. Function pointers pass functions as parameters or store addresses, and are used to implement dynamic calls to functions. Understanding function features and techniques is the key to writing efficient, maintainable, and easy to understand C programs.
Why do you need to call Vue.use(VueRouter) in the index.js file under the router folder?
Apr 05, 2025 pm 01:03 PM
The necessity of registering VueRouter in the index.js file under the router folder When developing Vue applications, you often encounter problems with routing configuration. Special...
What are the differences and connections between c and c#?
Apr 03, 2025 pm 10:36 PM
Although C and C# have similarities, they are completely different: C is a process-oriented, manual memory management, and platform-dependent language used for system programming; C# is an object-oriented, garbage collection, and platform-independent language used for desktop, web application and game development.
How to use XPath to search from a specified DOM node in JavaScript?
Apr 04, 2025 pm 11:15 PM
Detailed explanation of XPath search method under DOM nodes In JavaScript, we often need to find specific nodes from the DOM tree based on XPath expressions. If you need to...
What are the different ways of promoting H5 and mini programs?
Apr 06, 2025 am 11:03 AM
There are differences in the promotion methods of H5 and mini programs: platform dependence: H5 depends on the browser, and mini programs rely on specific platforms (such as WeChat). User experience: The H5 experience is poor, and the mini program provides a smooth experience similar to native applications. Communication method: H5 is spread through links, and mini programs are shared or searched through the platform. H5 promotion methods: social sharing, email marketing, QR code, SEO, paid advertising. Mini program promotion methods: platform promotion, social sharing, offline promotion, ASO, cooperation with other platforms.
