Simulink model prints callback messages to the Diagnostic Viewer, how do I print to the Command Window?

I am using a Simulink model PostLoadFcn to run a MATLAB function when the model is opened.

The callback invokes:

PostLoadFcnTest();

When the model is opened (either via double‑clicking the .slx file or using open_system(modelname)), none of the usual printing mechanisms work.

Instead, all output appears in the Diagnostic Viewer.

Here is my callback setup:

Every attempt to print to the Command Window is redirected to Diagnostic Viewer:

• disp()
• fprintf()
• fprintf(1, ...)
• evalin('base', ...)
• warning()
• Simulink.output.info()
• even onCleanup()

However, if I defer printing using a MATLAB timer, the message does appear in the Command Window:

My Questions

1. Is it expected behavior that PostLoadFcn suppresses stdout and forces all output into Diagnostic Viewer?
2. Is there any official MATLAB/Simulink supported way to print to the Command Window directly from PostLoadFcn without requiring changes to Diagnostic Viewer configuration?(Besides the timer workaround.)
3. Is there a recommended callback alternative to PostLoadFcn that runs after model is opened AND allows normal stdout printing?
4. Is stdout intentionally locked during model load/update? If yes, is this documented anywhere?

Answer 1

[Oliver Jaehrig]

I believe this post from our Technical Support team clarifies this behavior:

https://www.mathworks.com/matlabcentral/answers/469921-why-do-fprintf-and-disp-not-show-in-the-command-window-when-called-from-simulink-callbacks-why

If you have any further questions, consider creating a Technical Support case.

[Viren Monpara]

Hi Oliver, thanks for getting back to me. The link you provided cleared things up for me. Really appreciate it!