How to define a constant in php

In PHP, use define("CONSTANT_NAME", value) to define a constant, and its value will not change during execution. Constant names follow the variable naming rules, and the value can be of any type.

Define constants in PHP

In PHP, a constant is a special variable whose value is Remains unchanged during script execution. To define a constant, you can use the following syntax:

<code class="php">define("CONSTANT_NAME", value);</code>

where:

• CONSTANT_NAME is the name of the constant. Constant names must follow the variable naming rules, that is, start with a letter, number, or underscore, and cannot be a reserved word in PHP.
• value is the value of the constant. Constant values ​​can be of any type, including strings, numbers, arrays, or Boolean values.

Example:

<code class="php">define("MY_CONSTANT", "Hello World");</code>

After defining a constant, you can use it like an ordinary variable:

<code class="php">echo MY_CONSTANT; // 输出 "Hello World"</code>

Notes:

• Once a constant is defined, its value cannot be changed.
• Constant names are case-sensitive.
• Constants can be defined anywhere, but it is generally recommended to define them at the beginning of the script for centralized management.
• You can use the const keyword instead of the define function to define constants, but the syntax is the same.

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