The function used to define constants in php is

The function that defines constants in PHP is define(), which receives a constant name, a value, and optional case-sensitive parameters. Constant names usually use uppercase letters, start with a letter or an underscore, and are case-sensitive. You can create case-insensitive constants by setting the case-sensitivity parameter to true.

Function to define constants in PHP

The function used to define constants in PHP is: define ().

Function prototype:

<code class="php">define(string $name, mixed $value, bool $case_insensitive = false) : bool</code>

Parameters:

• $name: Constant Name
• $value: The value corresponding to the constant
• $case_insensitive (optional): Whether to use case-insensitive constant names. Default is false.

Return value:

If the constant definition is successful, return true; otherwise, return false.

Usage example:

<code class="php">// 定义一个常量，命名为 "MY_CONSTANT"，值为 "Hello World"
define('MY_CONSTANT', 'Hello World');

// 使用常量
echo MY_CONSTANT; // 输出 "Hello World"</code>

Constant naming rules:

The constant name must start with a letter or an underscore, and can be followed by letters, numbers, or underscores. Constant names are usually uppercase to distinguish them from variables.

Case sensitivity:

By default, constant names are case-sensitive. For example, MY_CONSTANT and my_constant are two different constants.

Case-insensitive:

Case-insensitive can be created by setting the $case_insensitive parameter to true constant. For example:

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

In this way, MY_CONSTANT and my_constant will refer to the same constant value.

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