C++ Const Pointer Usage

cpp_const_usage.cpp

//------------------------------------------------------------------------------------------------------------------------------

struct MyType
{
    int x = 0;
    void Mutate() { ++x; }
};

//------------------------------------------------------------------------------------------------------------------------------

int main()
{
    MyType a, b;

    // Example #1 - No const usage
    MyType* example1 = &a;
    example1 = &b;          // OK: Pointer value (address) is mutable
    example1->Mutate();     // OK: Object is mutable

    // Example #2 - Pointer value (address) is const, object remains mutable
    // NOTE: In C#, this is equivalent to using readonly with reference types
    MyType* const example2 = &a;
    example2 = &b;          // ERROR: Pointer value (address) is const
    example2->Mutate();     // OK: Object is mutable

    // Example #3 - Pointer value (address) is mutable, object is const
    const MyType* example3 = &a;
    example3 = &b;          // OK: Pointer value (address) is mutable
    example3->Mutate();     // ERROR: Object is const

    // Example #4 - Pointer value (address) and object are both const
    // NOTE: In C#, this is equivalent to using readonly with value types
    const MyType* const example4 = &a;
    example4 = &b;          // ERROR: Pointer value (address) is const
    example4->Mutate();     // ERROR: Object is const
}

//------------------------------------------------------------------------------------------------------------------------------