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c++pointersreference
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Reputation: 37

Reference to pointer (int * const & arg)

What is this exactly:

int * const & arg

Is this

By the way, const references does not make any sense to me. I thought you can not change references after they are declared...

Upvotes: 1

Views: 205

Answers (2)

eerorika
eerorika

Reputation: 238401

Is this

a reference to an int pointer?

No, because there is const.

a reference to a const int pointer?

Yes. It is better to use the same order as the declaration except in reverse to be clear: A

reference to a const pointer to int.
&              const *          int

Compared to the original, non reverse order:

int * const &

a const reference to an int pointer?

a const reference to an const int pointer?

There is technically no such thing as "const reference".

Although often people use it to mean reference to const. With such interpretation, a const reference to an int pointer is same as a reference to const int pointer. Also, with such interpretation, const reference to const has meaningless repetition of const.

Upvotes: 1

Gary Allen
Gary Allen

Reputation: 1380

arg is a reference to an int pointer, where that pointer itself is constant.

When declaring arg, you will notice that (because it is a reference) it must be initialized, as references cannot reference nothing.

An easy way to see this is by using an example:

int x;
int* const ptr = &x;
// declare an integer pointer which is constant i.e. the address it stores does not change,
// and initialize this address to the address of x

int* const& arg = ptr;
// declare a reference variable called arg, which references an integer pointer which is constant,
// the same type that ptr is, and then make it reference our ptr variable

Since the const argument is after the "*" in your line of code, you are telling C++ that the pointer itself is constant. However, if we were to write either

const int* & arg = ...

or

int const* & arg = ...

we would be telling C++ that the pointer is pointing to data (in this case an integer) which is constant. Further, if we wrote the following

int const* const & arg = ...

we would be telling C++ that the address the pointer stores is constant, and that this address points to an integer which is also constant.

Hope this helped!

Upvotes: 0

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