How to define constants in php

Defining constants in PHP requires the use of the define() function, which specifies the name and value of the constant, and optionally sets whether it is case-insensitive. When accessing a constant, simply use its name. Constant names are usually named in uppercase letters and cannot be changed.

How to define constants in PHP

Constants are used in PHP to store unchangeable values. Defining a constant is very simple, just use the define() function.

Syntax:

<code class="php">define(name, value, [case-insensitive]);</code>

Parameters:

• name: The name of the constant, Must be a valid PHP identifier.
• value: The value of the constant, which can be any data type.
• case-insensitive (optional): If set to true, the name of the constant will be case-insensitive.

Example:

<code class="php">define('PI', 3.14159265); // 定义一个浮点常量
define('TAX_RATE', 0.08); // 定义一个数字常量
define('COMPANY_NAME', 'Acme Corp.'); // 定义一个字符串常量</code>

Accessing constants:

A defined constant can be accessed directly using its name.

<code class="php">echo PI; // 输出 3.14159265
echo TAX_RATE; // 输出 0.08
echo COMPANY_NAME; // 输出 Acme Corp.</code>

Note:

• The name of a constant must start with a letter or underscore and cannot contain special characters.
• Once defined, constants cannot be modified or redefined.
• Constants can be accessed anywhere in the script.
• Constant names usually use uppercase letters to indicate their unchangeable nature.

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