Confusion about ROS2 parameters in MATLAB Coder

Hello everyone,

my confusion stems from the fact, that is seems not be possible to get array-valued parameters from a node. I use the following MWE-node which gets code generated with MATLAB Coder (codegen).

function myNode() %#codegen

nodeParams.gains = [0.5, 1.0, 2.0];

node = ros2node("/my_node", Parameters=nodeParams);

r = ros2rate(node, 10);

while true

[gains, ok] = getParameter(node, "gains", Datatype="double");

if ok

fprintf("First gain: %f\n", gains(1));

else

fprintf("Status is false\n");

end

waitfor(r);

end

end

This will successfully generate code, which can be compiled into a standlaone ROS2 node. Analyzing the node:

name@host:~/ros_ws$ ros2 param get /my_node gains

Double values are: [0.5, 1.0, 2.0]

Which means, that the parameter is set correct. But the node will repeatedly print:

Status is false

The code generation will also fail when actively trying to index into gains(2). I see from the Simulink-Coder documentation that there you are able to specify the datatype="double[]" which would make it clear that i want to read an array of doubles. But this is not allowed for the getParameter method. Does this mean, that it is simply not possible?

I am looking for some clarification on this topic, or possible workarounds. Thank you :)

Answer 1

[Umar]

Hi @Sönke,

This is a real, documented limitation — not something wrong with your code. The getParameter reference page states that for the code-generation syntax, the Datatype name-value argument only supports these return types: int64, logical, string, char, or double. There's no array variant (double[], etc.) offered for this argument, unlike the Simulink equivalent.

By contrast, the Simulink Get Parameter block for ROS 2 explicitly supports array types — its Data type parameter can be set to uint8[], double[], int64[], or boolean[], and it even has a Maximum length setting specifically for sizing the array output.

So the asymmetry you found is accurate: ros2node's Parameters argument and setParameter happily accept and publish array-valued parameters (which is why ros2 param get shows your array correctly), but the MATLAB Coder-facing getParameter function was never given an array-capable Datatype option. That mismatch is almost certainly why your generated code gets status = false — the codegen path is expecting a scalar double and the type resolution fails silently at runtime rather than erroring at compile time.

Workarounds:

1. Split the array into individual scalar parameters (gain1, gain2, gain3, ...) and call getParameter once per scalar with Datatype="double". This is the most direct fix given the current API. 2. If an array parameter is a hard requirement, use Simulink + Simulink Coder instead — the Get Parameter block natively supports double[] with a configurable max length.

Worth filing this as feedback to MathWorks directly, since as of the current documentation there's no array support in the MATLAB Coder-facing getParameter function — only in the Simulink block.

See attached PDF for direct documentation references and quotes supporting this.