I am learning about classes in C++ and know that non-static member functions have implicit this parameter. My first question is that does constructor also have an implicit this parameter just like non-static member functions. Note that i am not asking whether we can use this inside a ctor as i already know that we can use this inside a ctor.
Next, I know that inside a const qualified non-static member function for a class X, the type of this is const X*. And for a non-static member function(without const qualified), the type of this is X*. Similarly, inside the ctor the type of this is always X*. Here comes the deeper question.
We know that when we call a non-static member function(say like obj.func()), then the address of the object named obj is implicitly passed to the implicit this parameter of the method func. So this explains "where the this comes from in case of non-static member function".
Now, lets apply the same thing to constructors. For example, say we create an object of class X using default ctor like:
X x; //does the default ctor also have an implicit this parameter to which the address of x is passed?
My second question is: Does the same thing happen to ctors? Like, the address of x is passed to an implicit parameter of the default ctor. My current understanding is that ctors don't have an implicit this parameter. So when we write X x;, the address of x is not passed as an argument because the object is not created yet and so it doesn't make sense to pass its address. But from the standard we know that inside a ctor we can use the this pointer. So my second question essentially is that, if ctors don't have an implicit this parameter then where does the this in the statement this->p = 0; come from? We know that before using any name(like variable name) in C++, we must have a declaration for that name. So where is the declaration for this? Does the compiler implicitly declares the this in case of ctor? I mean, in case of non-static member function, i can understand that they have the declaration for this as the implicit this parameter but what happens in ctors? How inside ctors we're able to use the name this without having a declaration for that?
struct Name
{
private:
int p = 0;
int k = 0;
void func() //func is a non-static member function and so have an implicit this parameter
{
this->k = 0; // the "this" here comes from implicit this parameter
}
Name()
{
this->p = 0; //where does the "this" comes from here since ctor don't have implicit this parameter
}
};
My third question is that is the concept of implicit this parameter an implementation detail or does the standard says that non-static member function will have an implicit this parameter.
Summary
Do ctors have an implicit this parameter? This first question can also be phrased as "Do ctors also have an implicit object parameter?".
The standard says that we can use
thisinside a ctor. But where does thatthiscome from. For example, in case of a non-static member function, we know thatthiscomes from the implicit this parameter, but in case of ctors, since ctors don't have an implicitthisparameter, where does thatthisthat we're allowed to use inside ctor come from.Is the concept of implicit
thisparameter an implementation detail or does the standard say that all non-static member functions have an implicit this parameter, in which case, ctors are also allowed by implementations to have an implicit this parameter.
Edit:
The most important part(IMO) of this question is that how are we able to use the name this inside a ctor? For example when we write:
this->p = 0; //here "this" behaves like a name
In the above statement this behaves like a name. And we know that before using any name(like variable name) in C++, we must have a declaration for that name. So where is the declaration for this? Does the compiler implicitly declares the this in case of ctor? I mean, in case of non-static member function, i can understand that they have the declaration for this as the implicit this parameter but what happens in ctors? How inside ctors we're able to use the name this without having a declaration for that?
