MATLAB Coder generated MEX file throws an error that "Index exceeds matrix dimensions" although the code runs in MATLAB without error

I'm trying to use MATLAB Coder to generate C/C++ code for my MATLAB code. However, when I try to execute the MEX file generated by MATLAB Coder, it throws an error that for a specific variable that the index exceeds matrix dimensions:

>> myCode_mex
Index exceeds matrix dimensions. The array 'A' is empty and therefore has no valid indices.

The error stack points to the following MATLAB source code where I perform array extension:

n = length(A);
if n < buffSize
   A(n+1) = data;

The same code however runs in MATLAB without any issues. Why does this happen?

Answer 1

[MathWorks Support Team]

This is fundamental difference between MATLAB execution and code generation. Code generation does not support increasing the size of an array through left-hand-side indexing out-of-bounds (except in some circumstances where the index is exactly "end+1"). See the "Incompatibility with MATLAB in Matrix Indexing Operations for Code Generation" section in the following documentation:

Incompatibilities with MATLAB in Variable-Size Support for Code Generation

Which states that "Code generation does not support increasing the size of an array over time.".

Try This Workaround:

If 'A' is variable-sized (due to coder.varsize in the constructor), the you can grow 'A' by assigning to it completely:

Instead of:

A(n+1) = data;

Use:

A = [A, data];