如何正确初始化std :: array的向量？

Question

Firstly, I have a template data structure which can access elements using numeric indices. The indices can be negative.

class RangeList
{
public:
    RangeList(PosType off_min, PosType off_max)
        : _off_min(off_min)
        , _off_max(off_max)
        , data(off_max - off_min + 1) {}

    T& operator[] (PosType i)
    { return data[i-_off_min]; }

    const T& operator[] (PosType i) const
    { return data[i-_off_min]; }

    size_t size()
    { return data.size(); }

protected:
    PosType _off_min;
    PosType _off_max;
    std::vector<T> data;
};

I use C++11 std::array to represent some data profile of fixed length:

typedef std::array<float, std::numeric_limit<uint16_t>::max()> ProfileType;

The question raises when these two things combined together:

typedef RangeList<ProfileType> ProfileRangeList;

Inside RangeList , the data member will be of type vector<array<float, 65536> > .

I noticed, if you create a std::array on the stack, its contents will be uninitialized, and you need to explicitly set its content to zero. So what happens if the std::array is a value type of std::vector?

In my test code, it seems the contents are magically initialized to zeroes, but I don't know if it obeys language standard and is reliable and reproducible.

Answer 1

I suppose your If you create array on the stack means something akin to:

std::array<T,s> arr;

This is also valid, though:

std::array<T,s> arr {};

Which will value-initialize every field. And that's what vector does (to each of its array elements), so you're safe.