


Detailed explanation of php custom/system/class constant code examples
Let’s look at a piece of code first:
<span style="font-size:18px;"> <?php // php常量:分为以下四种 //(1)、自定义常量: // 必须用函数define()定义 // define() 函数 - 它使用三个参数: // 首个参数定义常量的名称 // 第二个参数定义常量的值 // 可选的第三个参数规定常量名是否对大小写敏感。默认是 false,对大小写敏感。 // 定义完后其值不能再改变了 // 使用时直接用常量名,不能像变量一样在前面加$s // 实例代码: define("GREETING", "Welcome to W3School.com.cn!"); echo "对大小写敏感:".GREETING."<br/>"; //第三个参数为 true ,对大小写不敏感 define("GREETING", "Welcome to W3School.com.cn!", true); echo "对大小写不敏感:".greeting."<br/>"; //(2)、系统常量: // PHP_VERSION:当前解析器的版本号 // PHP_OS:执行当前PHP版本的操作系统名称 // 可以直接拿来使用,例如要查看执行当前PHP版本的操作系统名称,就可以写成 echo PHP_OS // 实例代码: echo "<br/>"; //输出当前解析器的版本号 echo "当前解析器的版本号是: ".PHP_VERSION; echo "<br/>"; //输出执行当前PHP版本的操作系统名称 echo "当前操作系统是: ".PHP_OS; echo "<br/>"; // 输出圆周率 echo M_PI; echo "<br/>"; // 输出科学常数e echo M_E; echo "<br/>"; // 输出以2为底e的对数 echo M_LOG2E; echo "<br/>"; // 输出以10为底e的对数 echo M_LOG10E; echo "<br/>"; // 输出2的自然对数(常数e为底数的对数叫做自然对数) echo M_LN2; echo "<br/>"; // 输出10的自然对数 echo M_LN10; echo "<br/>"; //(3)、php类常量 class MyClass{ //类常量,用constant修饰,不带 const cons1 = 'constant value'; function showCons1() { echo self::cons1."<br/>"; } } //常量的表示形式: 类名::常量名 echo "<br/>类常量值为:".MyClass::cons1."<br/>"; ?> </span>
1. If two identical constants are defined, which one will work, the former or the latter?
The former works because a constant cannot be redefined or undefined once it is defined.
2. What are the differences between constants and variables?
1) There is no $ sign before constants;
2) Constants can only be defined through define(), not assignment statements;
3) Constants can be defined and accessed anywhere, while variables have global and local;
4) Once a constant is defined, it cannot be redefined or undefined, while a variable is redefined through assignment;
5) The value of a constant can only be scalar data, and the database type of the variable There are 8 primitive data types.
The above is the detailed content of Detailed explanation of php custom/system/class constant code examples. For more information, please follow other related articles on the PHP Chinese website!

PHP is widely used in e-commerce, content management systems and API development. 1) E-commerce: used for shopping cart function and payment processing. 2) Content management system: used for dynamic content generation and user management. 3) API development: used for RESTful API development and API security. Through performance optimization and best practices, the efficiency and maintainability of PHP applications are improved.

PHP makes it easy to create interactive web content. 1) Dynamically generate content by embedding HTML and display it in real time based on user input or database data. 2) Process form submission and generate dynamic output to ensure that htmlspecialchars is used to prevent XSS. 3) Use MySQL to create a user registration system, and use password_hash and preprocessing statements to enhance security. Mastering these techniques will improve the efficiency of web development.

PHP and Python each have their own advantages, and choose according to project requirements. 1.PHP is suitable for web development, especially for rapid development and maintenance of websites. 2. Python is suitable for data science, machine learning and artificial intelligence, with concise syntax and suitable for beginners.

PHP is still dynamic and still occupies an important position in the field of modern programming. 1) PHP's simplicity and powerful community support make it widely used in web development; 2) Its flexibility and stability make it outstanding in handling web forms, database operations and file processing; 3) PHP is constantly evolving and optimizing, suitable for beginners and experienced developers.

PHP remains important in modern web development, especially in content management and e-commerce platforms. 1) PHP has a rich ecosystem and strong framework support, such as Laravel and Symfony. 2) Performance optimization can be achieved through OPcache and Nginx. 3) PHP8.0 introduces JIT compiler to improve performance. 4) Cloud-native applications are deployed through Docker and Kubernetes to improve flexibility and scalability.

PHP is suitable for web development, especially in rapid development and processing dynamic content, but is not good at data science and enterprise-level applications. Compared with Python, PHP has more advantages in web development, but is not as good as Python in the field of data science; compared with Java, PHP performs worse in enterprise-level applications, but is more flexible in web development; compared with JavaScript, PHP is more concise in back-end development, but is not as good as JavaScript in front-end development.

PHP and Python each have their own advantages and are suitable for different scenarios. 1.PHP is suitable for web development and provides built-in web servers and rich function libraries. 2. Python is suitable for data science and machine learning, with concise syntax and a powerful standard library. When choosing, it should be decided based on project requirements.

PHP is a scripting language widely used on the server side, especially suitable for web development. 1.PHP can embed HTML, process HTTP requests and responses, and supports a variety of databases. 2.PHP is used to generate dynamic web content, process form data, access databases, etc., with strong community support and open source resources. 3. PHP is an interpreted language, and the execution process includes lexical analysis, grammatical analysis, compilation and execution. 4.PHP can be combined with MySQL for advanced applications such as user registration systems. 5. When debugging PHP, you can use functions such as error_reporting() and var_dump(). 6. Optimize PHP code to use caching mechanisms, optimize database queries and use built-in functions. 7


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

AI Hentai Generator
Generate AI Hentai for free.

Hot Article

Hot Tools

ZendStudio 13.5.1 Mac
Powerful PHP integrated development environment

SublimeText3 Linux new version
SublimeText3 Linux latest version

VSCode Windows 64-bit Download
A free and powerful IDE editor launched by Microsoft

SublimeText3 Mac version
God-level code editing software (SublimeText3)

Dreamweaver CS6
Visual web development tools