问题
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?
回答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]();
回答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.
回答3:
int is not a class, it's a built in data type, therefore no constructor is called for it.
来源：https://stackoverflow.com/questions/3575458/does-new-call-default-constructor-in-c