'Does new[] call default constructor in C++?

When I use new[] to create an array of my classes:

int count = 10;
A *arr = new A[count];

I see that it calls a default constructor of A count times. As a result arr has count initialized objects of type A. But if I use the same thing to construct an int array:

int *arr2 = new int[count];

it is not initialized. All values are something like -842150451 though default constructor of int assignes its value to 0.

Why is there so different behavior? Does a default constructor not called only for built-in types?

c++arraysstandardsnew-operator


Solution 1:[1]

See the accepted answer to a very similar question. When you use new[] each element is initialized by the default constructor except when the type is a built-in type. Built-in types are left unitialized by default.

To have built-in type array default-initialized use

new int[size]();

Solution 2:[2]

Built-in types don't have a default constructor even though they can in some cases receive a default value.

But in your case, new just allocates enough space in memory to store count int objects, ie. it allocates sizeof<int>*count.

Solution 3:[3]

int is not a class, it's a built in data type, therefore no constructor is called for it.

Solution 4:[4]

Primitive type default initialization could be done by below forms:

    int* x = new int[5];          // gv gv gv gv gv (gv - garbage value)
    int* x = new int[5]();        // 0  0  0  0  0 
    int* x = new int[5]{};        // 0  0  0  0  0  (Modern C++)
    int* x = new int[5]{1,2,3};   // 1  2  3  0  0  (Modern C++)

Sources

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Source: Stack Overflow

Solution Source
Solution 1 Community
Solution 2 Suma
Solution 3 Hamid Nazari
Solution 4 SridharKritha

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