c++ dynamic memory allocation using “new”

Question

I\'m new to C++, trying to learn by myself (I\'ve got Java background).

There\'s this concept of dynamic memory allocation that I can assign to an array (for example

Answer 1

When you know the size of an array at compile time you can declare it like this and it will live on the stack:

int arr[42];

But if you don't know the size at compile time, only at runtime, then you cannot say:

int len = get_len();
int arr[len];

In this case you must allocate the array at runtime. In this case the array will live on the heap.

int len = get_len();
int* arr = new int[len];

When you no longer need that memory you need to do a delete [] arr.

std::vector is a variable size container that allows you to allocate and reallocate memory at runtime without having to worry about explicitly allocating and freeing it.

int len = get_len();
std::vector v(len); // v has len elements
v.resize(len + 10); // add 10 more elements to the vector