What is the Difference Between define() and const Keyword in PHP ?
Last Updated :
13 Feb, 2024
In PHP, both define( )
and const
Keywords are used to define constants, which are identifiers with unchanging values. However, they have differences in terms of usage, scope, and flexibility.
Syntax
// Using define() function
define("CONSTANT_NAME", value);
// Using const keyword (outside of class)
const CONSTANT_NAME = value;
Important Points
- Constants defined using
define( )
are global and can be defined anywhere in the script, including within functions or conditionals.
- Constants defined using
const
Keywords are class constants and can only be defined within classes or interfaces.
A define()
method is evaluated at runtime, whereas const
the keyword is evaluated at compile time.
- Constants defined using
const
keywords are case-sensitive, whereas those defined using define()
are case-insensitive by default.
Difference between define() and const
define() |
const keyword |
Defines constants at runtime |
Defines class constants at compile time |
Can be defined anywhere in the script |
Can only be defined within classes or interfaces |
Case-insensitive by default |
Case-sensitive by default |
Global scope |
Class scope |
Usage
- Dynamic vs. Static Definition:
define()
allows dynamic definition of constants at runtime, while const
keyword allows static definition within class or interface definitions.
- Scope: Constants defined using
define()
are global and can be accessed from anywhere in the script, while constants defined using const
keyword are scoped to the class or interface in which they are defined.
- Case Sensitivity: Constants defined using
const
keyword are case-sensitive by default, whereas those defined using define()
are case-insensitive unless explicitly specified.
Example:
// Using define() to define a Global constant
define("PI", 3.14);
// Using const keyword to define a Class constant
class Math {
const PI = 3.14;
}
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