Is this simple example considered as RAII

Question

And peformance-wise, are there some better ways to do that?

for example, create a class/struct called arraydata, it allocates some aligned memory for use (though a pointer provided by .dataPtr):

class arraydata//to allocate some memory, 
               //and return a pointer to that block of memory
{
    void *dataPtrV;

  public:

    double *dataPtr;

    arraydata(int a, int b)
    {
        dataPtrV=_aligned_malloc(a*b*sizeof(double),32);
        dataPtr=(double *)dataPtrV;
    }

    ~arraydata()
    {
        _aligned_free(dataPtrV);
        dataPtrV=NULL;
        dataPtr=NULL;
    }   
};

Then call it by:

     arraydata X(30,20);

Answer 1

Yes, that would be considered RAII - the resource is acquired in the constructor and released in the destructor.

I'm not sure why you're storing both a void* and a double* though - only a double* should suffice.

Also, be extremely careful when copying your class as that will easily lead to leaks and freeing already freed data.

Anyway, this can also be done using std::unique_ptr which is more idiomatic and without the downfalls of your class:

struct aligned_free {
  void operator()(void* p) {
     _aligned_free(p);
  }
};

template<typename T>
T* aligned_malloc(std::size_t size, std::size_t alignment) {
  return static_cast<T*>(_aligned_malloc(size * sizeof(T), alignment));
}

std::unique_ptr<double, aligned_free> make_array_data(int a, int b) {
    return std::unique_ptr<double, aligned_free>(aligned_malloc<double>(a*b, 32));
}

auto arraydata = make_array_data(30, 20);

---

Here's your class without void*:

class arraydata//to allocate some memory, 
               //and return a pointer to that block of memory
{

  public:

    double *dataPtr;

    arraydata(int a, int b)
    {
        dataPtr=static_cast<double*>(_aligned_malloc(a*b*sizeof(double),32));
    }

    ~arraydata()
    {
        _aligned_free(dataPtr);
    }   
};