MATLAB Answers

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

15 views (last 30 days)
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?

  0 Comments

Sign in to comment.

Accepted Answer

Ryan Livingston
Ryan Livingston on 31 Mar 2020
Edited: Ryan Livingston on 31 Mar 2020
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};

  3 Comments

Matt Shellhammer
Matt Shellhammer on 31 Mar 2020
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
Ryan Livingston on 31 Mar 2020
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.

Sign in to comment.

More Answers (0)

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!