C++ unique_ptr to array element

Question

I had a function that returns a unique_ptr to an array element, and I noticed the original variable was not getting updated.

Why does this work (a[5] == 6 after):

int a[10];

for (size_t i = 0; i < 10; i++)
{
    a[i] = i;
}

int* ap = &a[5];

*ap += 1;

But

int a[10];

for (size_t i = 0; i < 10; i++)
{
    a[i] = i;
}

unique_ptr<int> ap = make_unique<int>(a[5]);

*ap += 1;

Does not update the original array element? (a[5] == 5 ):

Answer 1

The function std::make_unique<T> constructs a new object .

Quoting:

Constructs an object of type T and wraps it in a std::unique_ptr.

Therefore, your statement

unique_ptr<int> ap = make_unique<int>(a[5]);

creates another integer ( T = int ) and initializes it with the value of the expression a[5] .

So, when you operate on the pointer ap you are actually modifying another integer (a copy of a[5] ).