Question

In C++11 we have a new std::array, similar to the boost::array. Example:

std::array<int, 5> fiveInts;

If I would like to use this new arrays in two ways:

1. Allocate an array on the stack.
2. Allocate an array on the heap.

How to achieve that syntactically? Can that 5 be a variable or only a const?

Answer 1

Template arguments must always be known at compile time. The size of a std::array cannot be a variable.

The best way to manage a contiguous buffer of values on the heap is via std::vector, which gives you run-time sizing of the size of the buffer.

std::array<int, 5> fiveInts; creates an array of 5 elements on the stack (in automatic storage). std::vector<int> fiveInts(5); creates a managed buffer of 5 ints on the heap (in the free store).

You could create the full std::array on the heap via calling new, but I would advise against it. std::arrays main advantage is that it allows stack-based (or internal-to-a-class-based) storage.