static const

Learn to define class constants with static const.

static const

A static const member is an immutable constant at the class level. Integral types (int, char, bool) can be initialized directly inside the class body.

Example: static const int MAX = 100;. This requires no separate outside definition. More complex types still need an outside definition. static const members can be used as compile-time constants: as array sizes or case labels. The value cannot be changed later, making them suitable for configuration constants.

Using static const

Because static const members are compile-time constants, they can be used as array sizes: int data[MAX];. This is ideal for values that will not change at runtime.

For example, in a Config class you can define static const int MAX_USERS = 50; and write int users[MAX_USERS];. Modern C++ also offers constexpr, but static const is still common and compatible. It guarantees the constant cannot be modified.

Exercise Add a static const to the Config class

Define a Config class. Under public: add static const int MAX = 5;. In main declare an array int data[Config::MAX]; and write std::cout << Config::MAX;.

Show example solution

#include <iostream>

class Config {
public:
    static const int MAX = 5;
};

int main() {
    int data[Config::MAX];
    std::cout << Config::MAX;
    return 0;
}

Test yourself

Which can be initialized inside the class?
```
class Config { ??? };
```
- static int max = 100;
- static const int MAX = 100;
- const int max;
- int max = 100;
Show answer

static const int MAX = 100; — A static const integer can be initialized inside the class.
Match each declaration to its type

static const int MAX = 100;

In-class constant
MAX

Compile-time constant
static int count;

Modifiable
const int x;

Instance constant

Complete the constant value

class Config { public: static const int MAX = ____; };

Show answer

class Config { public: static const int MAX = 100; };

Next lesson: inline static

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