# C++ Const correctness

**[Const correctness](https://en.cppreference.com/w/cpp/language/const_cast)** means using `const` to document and enforce which functions and pointers should not modify their targets. A `const` member function promises not to modify the object, and a `const` parameter or reference promise the same to callers. This enables compiler checking and clarifies intent.

Apply `const` to all parameters and member functions that don't need to modify their targets for clarity and to enable passing const objects.

## Example

This example shows const member functions and const references enforcing immutability.

```cpp
// compile: g++ -o const const.cpp
// run: ./const
// description: const correctness prevents accidental mutations

#include <iostream>
#include <string>

class User {
private:
    std::string name;
public:
    User(const std::string& n) : name(n) {}
    
    const std::string& getName() const {
        return name;  // const function, const return
    }
    
    void updateName(const std::string& n) {
        name = n;  // non-const function
    }
};

int main() {
    const User u("Alice");
    std::cout << u.getName() << "\n";  // can call const methods
    // u.updateName("Bob");  // error: cannot call non-const on const object
    
    User u2("Charlie");
    u2.updateName("Dave");  // OK on non-const
    std::cout << u2.getName() << "\n";
    
    return 0;
}
```