What is the usage of const in php

const is a keyword in PHP, which is used to define constants. The syntax is "const constant name = constant value;"; when the const keyword defines a constant, it can only contain scalar data (bool, int, float, string). Once a constant is defined, it cannot be changed or undefined.

The operating environment of this tutorial: windows7 system, PHP7.1 version, DELL G3 computer

const is a keyword in php, is Used to define constants.

In PHP, you can use the const keyword or the define() function to define a constant. The function define() allows a constant to be defined as an expression, while the const keyword has some restrictions. Once a constant is defined, it cannot be changed or undefined.

When using the const keyword to define a constant, it can only contain scalar data (bool, int, float, string). A constant can be defined as an expression or as an array. You can also define resource as a constant, but this should be avoided as it may cause unpredictable results.

Compared with variables, constants have the following characteristics:

• There is no dollar sign ($) in front of the constant;

• Constants can only be defined using define() and const;

• The scope of constants is global;

• Once defined, constants cannot be redefined or undefined.

The syntax of const keyword to define constants:

const 常量名 = 常量值;

Example:

<?php
    const url = &#39;https://www.php.cn/&#39;;
    echo url;
?>

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