Can a pointer pointing to a const also point to a non const? [duplicate]

Question

As we know in reference, a const can have a reference to either a const or non-const. However I have a question for the following pointer:

#include<iostream> using namespace std; int main() { const double pi = 3.14; const double *cptr = &pi; //we point to a const double (above) double dval = 3.14; cptr = &dval; cout<<*cptr<<endl; }

What I am not understanding is "const double *cptr" if we read it from right to left we have cptr is a pointer that points to a const double.

However, below we have double dval = 3.14; with cptr = &dval; double dval is not a constant, from what I am understanding we can still point to a non constant correct?

The const in const double *cptr simply means "cptr can not change the double it points to". — Drew Dormann
– Drew Dormann, Commented Jul 2, 2022 at 18:12
...or to put it slightly differently, const doesn't really mean "constant" nearly as much as it means "read only". Having a read-only pointer to a writable item just means you can't write to the item via that pointer. — Jerry Coffin
– Jerry Coffin, Commented Jul 2, 2022 at 18:46
"a const can have a reference to either a const or non-const" I hope you don't mean to have a non-const reference to a const variable — MatG
– MatG, Commented Jul 2, 2022 at 18:48
This is an example straight from the book C++ Primer where it is already explained thoroughly. There the author has explained this line by line in a very beginner friendly manner so the explanation can be looked up there. — Richard
– Richard, Commented Jul 2, 2022 at 19:13

Some programmer dude · Accepted Answer · 2022-07-02 18:08:58Z

2

That's perfectly fine.

After the reassignment

cptr = &dval;

it just means that you can't dereference the pointer cptr to modify what it points to.

In other words, it's not possible to do e.g.

*cptr = 2.72;

answered Jul 2, 2022 at 18:08

Some programmer dude

411k36 gold badges420 silver badges655 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

tall_call_9129 Over a year ago

Ok thank you! I thought because we specifically specified the pointer points to a const double we absolutely have to point to a double that is const. Thanks for clarifying!

463035818_is_not_an_ai · Accepted Answer · 2022-07-02 18:14:16Z

Similar to having a const & to a non-const object you can have pointers to const pointing to non-const objects.

Suppose you'd use a pointer rather than a reference for pass-by-reference, then this

 void foo(const double* p);

Means that the function cannot modify the pointee. Whether the passed pointer does actually point to a const double doesn't matter that much to the function, because anyhow it is not modifying it:

double dval = 3.14; foo(&dval);

After the function call, dval is still 3.14.

Collectives™ on Stack Overflow

Can a pointer pointing to a const also point to a non const? [duplicate]

2 Answers 2

1 Comment

Comments

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

Comments

Linked

Related