Creating array using emx array api with initialization to zero

I have MATLAB Coder project which contains emx arrays.

When I generate C code in MATLAB R2021a, Coder generates emxCreate function with calloc inside:

emxArray_Nodes *emxCreateND_Nodes(int numDimensions, const int *size)
{
  emxArray_Nodes *emx;
  int numEl;
  emxInit_Nodes(&emx, numDimensions);
  numEl = 1;
  for (int i = 0; i < numDimensions; i++) {
    numEl *= size[i];
    emx->size[i] = size[i];
  }
  emx->data = (Nodes *)calloc(static_cast<unsigned int>(numEl), sizeof(Nodes));
  emx->numDimensions = numDimensions;
  emx->allocatedSize = numEl;
  return emx;
}

But when I generate C code in MATLAB R2023b, Coder generates emxCreate funciotn with malloc:

emxArray_Nodes *emxCreateND_Nodes(int numDimensions, const int *size)
{
  emxArray_Nodes *emx;
  int numEl;
  emxInit_Nodes(&emx, numDimensions);
  numEl = 1;
  for (int i = 0; i < numDimensions; i++) {
    numEl *= size[i];
    emx->size[i] = size[i];
  }
  emx->data = static_cast<Nodes *>(
      malloc(static_cast<unsigned int>(numEl) * sizeof(Nodes)));
  emx->numDimensions = numDimensions;
  emx->allocatedSize = numEl;
  return emx;
}

In the second code memory for my struct arrays is allocated without initialization to zero. As a result, after updating MATLAB, code behaviour was changed.

How can I force MATLAB Coder R2023b to generate emx Create functions with calloc inside for initialization all struct array elements with zeros?

Answer 1

[Ezra Stein]

Hi Dmitri,

In R2023b we began generating emxArray allocation functions without zero-initializing their data. This was done as a performance enhancement because the generated code never actually relied on the zero-initialized data internally. Unfortunately, there is currently no way to enable the old behavior.

However, there are two possible workarounds:

1. Manually initialize the data to 0 after creating the emxArray. This is the simplest approach but it incurs the preformance overhead of doing an allocation followed by a zero-initialization.
2. Allocate memory via calloc manually, then wrap that memory in an emxArray using the emxCreateWrapper_<name> or emxCreateWrapperND_<name> utility functions. More details about this workflow can be found in the documentation here: https://www.mathworks.com/help/coder/ug/use-c-arrays-in-the-generated-function-interfaces.html#mw_1bf6258f-c070-4743-bb63-500d05e4542e

I am aware that the linked documentation page still states that the emxArray creation functions zero initialize the data. As a result, users have been relying on this behavior with an expectation that it will not change without warning. I am sorry for the inconvenience that this breaking change has caused.

I will discuss with our team to consider an enhancement that would allow users to enable the old behavior if desired.

Best,

-Ezra

[Dmitri Bliznuk]

Thank you for explanation