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How do I define and use constants in a class in PHP?

Hey everyone,
I'm currently working on a PHP project and I want to define and use constants within a class. I know that constants are like variables, but their values can't be changed once defined. This makes them perfect for storing values that remain constant throughout the execution of a script.

I'm wondering how I can define a constant within a class and then access it. Can anyone help me with this? I'd greatly appreciate it!

All Replies


I completely agree with User 1's explanation. Defining and using constants in a PHP class is indeed a useful feature. One thing to note is that constants are defined at the class level, and they are accessible throughout the class, including its methods.

Besides the numerical constants like PI mentioned by User 1, you can also define string constants or even arrays as class constants. This can be particularly handy when you have values that need to remain constant and shared among all instances of the class.

Here's an example where I define a string constant and an array constant within a class:

class MyClass {
const GREETING = "Hello, ";
const FRUITS = ['apple', 'orange', 'banana'];

public function greet($name) {
echo self::GREETING . $name;

public function printFruits() {
foreach (self::FRUITS as $fruit) {
echo $fruit . ", ";

In the above code, I've defined the constant `GREETING` as a string and `FRUITS` as an array. These constants can be accessed using the `self` keyword followed by double colons. In the `greet()` method, I concatenate the constant `GREETING` with the provided name to generate a greeting. In the `printFruits()` method, I loop through the constant `FRUITS` and print each fruit.

Feel free to try it out and let me know if you have any further questions!


Hey there!
Defining and using constants within a class in PHP is a straightforward process. To define a constant within a class, you need to use the `const` keyword followed by the constant name and value. Here's an example:

class MyClass {
const PI = 3.14;

public function calculateArea($radius) {
return self::PI * $radius * $radius;

In the above code, I've defined a constant named `PI` with a value of 3.14 inside the `MyClass`. To access this constant, I'm using the `self` keyword followed by the double colons to reference the constant within the class.

You can then use this constant anywhere within the class, just like any other variable or method. For example, in the `calculateArea()` method, I've multiplied the constant `PI` with the provided radius to calculate the area of a circle.

Hope that helps! Let me know if you have any more questions.

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