Fixed-sized C arrays with template parameter-dependent sizes

Question

I am working with a templated class, which I'd like to include fixed-sized data arrays whose size depends on the template parameter. A simplified example is

template<int D>
class Foo
{    
    private:
        int m_array[D*(D+1)];            
};

While variable-sized C arrays are understandably frowned upon in general, here they might be justifiable, since D is small and it's nice and clear how many values m_array holds (and that it cannot change size). My questions are

1. Is this in fact a justifiable use of variable-sized arrays in the first place?
2. Is this always bad practice, as these arrays are not universally supported by compilers?
3. Is there a clean alternative? One could use a std::vector and set the size in a constructor, which I'd argue makes the code less clear. Would it be preferable to use C++11's std::array , thus changing the relevant line in the example above to std::array<int,D*(D+1)> m_array; ?

Answer 1

Your example isn't a variable-length array , like what exists in C99. There, the size of the array is only known at runtime.

Here, you use a compile-time constant to set the size of the array. There is no problem with doing so. Go forth and enjoy.