Unhandled exception on user callback

Question

When I do the following:

 float name[512][512][3]

I get this big error which causes me to break. I'm using Visual Studio.

I noticed simply putting "static" in front causes the error to go away, but I want this to be an instance field. I'm not sure why this is happening -- the array isn't that big and I have a powerful machine.

Trying [512][512] breaks me, but [256][512] is totally fine.

I'm at my wit's end! Help please :)

Answer 1

The array is 3 MB (on most implementations of float). Objects of such size should only be allocated dynamically—3 MB is way too much for residing on the stack.

You have two options: one is to keep your class as-is, and make sure you only ever allocate it dynamically (using new, owned in a smart pointer).

The other, which I would prefer, is to use std::vector<float> instead of a 3-dimensional array, and implement the indexing around it as accessor functions. You could even wrap this vector & accessors in a class of their own, and use that as the type of your name data member.

The second option guarantees that the 3 MB of data will never reside in non-dynamic memory.

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Here's one possible sketch of such a 3D-accessible vector:

template <class T, size_t Dim1, Dim2, Dim3>
class Array3d
{
  std::vector<T> data;

public:
  Array3d() : data(Dim1 * Dim2 * Dim3) {}

  T& at(size_t idx1, size_t idx2, size_t idx3)
  { return data[idx1 * Dim2 * Dim3 + idx2 * Dim3 + idx3); }

  T at(size_t idx1, size_t idx2, size_t idx3) const
  { return data[idx1 * Dim2 * Dim3 + idx2 * Dim3 + idx3); }
};

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A more basic alternative would be to just dynamically allocate the array itself:

using Array2d = std::array<std::array<float, 3>, 512>;
std::unique_ptr<Array2d[]> name{new Array2d[512]};
name[i][j][k] = 42.0f;