Can I access an external (const) array within generated C++ code without copying the contents into a local array?

I have been generating code with massive constant arrays in the generated code using MATLAB coder code generation MATLAB to C++ code. I would like to define these arrays in an external header funtion instead of within the MATLAB code, a MATLAB class, or define it as a global variable. I would like to define it as a const int array in a external header function and then just access that array in generated code (avoiding generating the array every time a change to the MATLAB code is modified).

I know that I could use an external function to copy the array into a local array, however my goal is to avoid copying the elements. I would like to simply directly access the elements from a const int array within generated code by using

coder.target('RTW')

if coder.target('RTW')
    coder.cinclude('header.h');
    % x defined in header.h (const int x[5] = {1,2,3,4,5};)
else
    x = [1,2,3,4,5];
end

Any insight?

Answer 1

[Ryan Livingston]

With Embedded Coder you can use the function coder.storageClass to pull in that array as an imported extern global variable:

function useImportedArray
global importedArray;
coder.storageClass('importedArray','ImportedExtern');
t = sum(importedArray(:));
fprintf('Sum = %g\n', t);

% Do codegen
cfg = coder.config('dll');
cfg.GenerateExampleMain = "GenerateCodeAndCompile";
codegen useImportedArray -config cfg -globals {'importedArray', [7,8,8]} arrayConstant.c

arrayConstant.c

const double importedArray[] = {1.0, 2.0, 3.0};

[Matt Shellhammer]

I tested this and the result is a definition of "extern int importedArray[3];", is there a way to get the extern variable to be a "extern const int importedArray[3];"? I would like to keep the array as a const int.

[Ryan Livingston]

Unfortunately there's not a way to make it const. I've made an internal note so we can think about that for the future though.

[Matt Shellhammer]

Great, thank you!