在堆栈上创建对象

Question

I have a class which contains a large vector

class myClass
{
public:
    myClass(int size)
private:
    vector<int> myVector;
}

myClass::myClass(int size)
{
    myvector = vector<int>(size);
}

If I call myClass o(100000) the object is created on the stack. However, what is exactly on the stack ? How much memory do I allocate from the stack ? The contents of the vector should be allocated on the heap, right ?

Can someone explain to me what exactly is on the stack and what is on the heap ?

Answer 1

Essentially you can generalize std::vector as

template<typename T>
struct vector {
    T* data;
    size_t size;
    size_t capacity;
};

Individual implementations may vary but they'll usually look something like the above.

So it's just this vector-container that is created on the stack, the array in which the data will be held is drawn from the heap.

--- Edit ---

For a given stack variable, you can tell how much stack space it requires with the sizeof operator, eg

myClass o(100000);
std::cout << "o's size is " << sizeof(o) << "\n";