Question

Does it matter if the constructor/destructor implementation is provided in the header file or the source file? For example, which way is preferred and why?

Way 1:

class Singleton
{
  public:
    ~Singleton() { }

  private:
    Singleton() { }
};

Way 2:

class Singleton
{
  public:
    ~Singleton();

  private:
    Singleton();
};

In the source .cc file:

Singleton::Singleton()
{
}

Singleton::~Singleton()
{
}

Initially, I have the implementation in a source file, but I was asked to remove it. Does anyone know why?

Answer 1

It does not matter, but usually it’s better (in my humblest of opinions) to define them in the .cpp file, in order to hide the implementation from users of the class.