use of brackets after contructor and destructor

[agyBeginner]

Hello, what is the difference between

 Mammal();
~Mammal();

and

 Mammal() {}
~Mammal() {}

Why it is not needed to put semicolons after the lines in the second piece of code.

Thanks in advance

[minomic]

The first two examples are invocations, while in the last two examples you are providing an empty implementation of both the constructor and the destructor.

[Peter87]

The first two examples are invocations

They are probably function declarations.

class Mammal
{
public:
	Mammal();
	~Mammal();
	// ...
};

It means they have to be defined elsewhere, outside the class definition.

Mammal::Mammal()
{
	// ...
}

Mammal::~Mammal()
{
	// ...
}

[agyBeginner]

Thank you very much for your responses.