What is the difference between PHP constants and variables?

What is the difference between PHP constants and variables?

• #Different definition methods: PHP variables have no defined keywords or functions and are defined when assigning values. PHP constants must be defined using the define() function.

• Different names: PHP variable names need to be modified with a dollar sign ($), but PHP constant names do not. It is recommended that PHP variable names be lowercase. When they consist of multiple words, the first letter of the first word should be lowercase, and the first letter of the remaining words should be uppercase. It is recommended that PHP constant names be in all uppercase letters.

• The meanings of values ​​are different: the value stored by PHP variables can be changed, while the value stored by PHP constants cannot be changed.

• Scope is not used: PHP variables are defined outside all functions and have global scope; when defined within functions, they have local scope. PHP constants are generally defined outside all functions and have super-global scope.

• The data type range is different: PHP variables can be of any data type, while PHP constants can only be scalar types (integer, float/double, string, boolean).

Sample code

/**
 * 常量定义
 */
define('ROOT_PATH', './web');

/**
 * 变量定义
 */
$root_path = './web';

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