Shared_ptr with array

Question

Hi all

Why p2 being int array is allocating same size as of int?

Should it not allocate 24*5 = 120?
https://code.sololearn.com/c0tdy0fXUAOb/?ref=app

Answer 1

"std::make_shared ()" doesn't use your implementation of "new" operator to allocate the storage for the object, it instead uses global placement new operator ( which can't be overloaded )

The place where your "new" is being used is to allocate memory ( 24 in this case ) to store internals like shared_count.

you can confirm this by making shared ptr for different types :
https://code.sololearn.com/ca97KJFS2CKI/?ref=app

--
some useful links :-

1. Placement new : https://en.cppreference.com/w/cpp/language/new#Placement_new

2. std::make_shared : https://en.cppreference.com/w/cpp/memory/shared_ptr/make_shared

Answer 2

Ketan Lalcheta yes, if you are working with C++20 ( or above )

make_shared<int[5]> ();
or
make_shared<int[]> (5);

Should work as intended.

Answer 3

It's because in your environment, a pointer IS an integer.
To actually allocate the memory, you would have to call ‘new int[5]’
I think they’re both pointers to an int. sizeof(int*) would be the same as sizeof(int**)

Answer 4

Okay... So

shared_ptr<int[]> p2 = make_shared<int[5]>();

Is proper to allocate array ?