## [How to debug your own Ansys Rocky Custom Modules -- \[Solver SDK\]](/blog/how-debug-your-own-ansys-rocky-custom-modules-solver-sdk) When developing your Ansys Rocky™ Custom Modules using the Rocky Solver SDK, running into errors or unexpected behaviors is part of the process. Whether you are extending particle behavior, creating custom post-processing tools, or integrating with external solvers, efficient debugging is essential to ensure your module works as intended. In this article, we will walk through a step-by-step approach to debugging your own custom modules -- from setting up your development environment to interpreting log messages and using external tools like Visual Studio for deeper inspection. ## 1. Use Rocky Simulation Log file for information Rocky software provides a simulation log file which contains simple information, such as hardware details, to more complex data about the simulation, such as particles, triangles, and contacts information; memory consumption and free memory; and other solver process information. These outputs can help you trace what your module is doing, which can be useful for debugging purposes. ![](https://developer.ansys.com/sites/default/files/inline-images/debugrockymodules_img1.png) *Example simulation log file location* Visit the [Rocky User Manual](https://ansyshelp.ansys.com/public/account/secured?returnurl=/Views/Secured/prod_page.html?pn=Rocky&pid=Rocky&lang=en)for more details about the Simulation log file. You can also find some information in a more simplified form in the **Simulation log panel** within Rocky, which displays any solver-related warnings, errors, or other information that happen during processing, no matter whether you are running your simulations using CPU or GPU resources. ![](https://developer.ansys.com/sites/default/files/inline-images/debugrockymodules_img2.png) *Simulation Log panel showing some warnings and information that was logged during processing* Visit the [Rocky User Manual](https://ansyshelp.ansys.com/public/account/secured?returnurl=/Views/Secured/prod_page.html?pn=Rocky&pid=Rocky&lang=en) for more details about the Simulation log panel. ## 2. Use Print Statements or Logging in your code Sometimes, the simplest way to check if your code is running as expected is to insert print/log lines in strategic parts. Examples of code lines to print: ```python ROCKY_MESSAGE_LOG("SPHModelAPIAddin: configure"); ROCKY_INFO_LOG("SPHModelAPIAddin: initialize_cuda"); ROCKY_WARNING_LOG("Text"); ``` In this way you can print values in the log and use the Rocky application to debug. ## 3. Use Auxiliary Scalars to identify calculations errors You can also create auxiliary scalars with intermediate values ​​to help you identify possible calculation errors and later visualize them during the simulation in the 3D view. ## 4. Check for compilation and Linking Errors To prepare your system for building custom modules for Rocky software using the Solver SDK, you need to install and set up a few components, including environment variables. - Ensure that all components were added correctly using the **Installation Guide Modules and Scripts** within **SDK and Modules (Full Package)** [in Ansys Customer Portal](https://download.ansys.com/currentReleases). - Always clean and rebuild if you are unsure. **Important:** Check the version of Solver SDK you are using and make sure it is the same as the Rocky software. Mixing packages from different versions may generate an error. ## 5. Use the VS Code to debug Ansys Rocky Custom Modules Below is a workflow you can follow for building and debugging your code: 1. Download and install **VS Code**. ***Note:** In this step-by-step, the version used was 1.67.2.* 2. Launch **VS Code** and install the following extensions: - **C/C ++ Extension Pack (Microsoft)** - **CMake (twxs)** - **CMake Tools (Microsoft)** 3. Close and Launch **VS Code** again. 4. Go to **File,** then **Open folder,** and open the *Module Folder*you are currently working on. 5. Configure the compiling options as shown below: ![undefined](https://developer.ansys.com/sites/default/files/inline-images/debugrockymodules_img3.png) 6. Click on Build: > This should compile the module with Debug info and also install the > .dlls and python file in the module's folder. If everything went right > during compilation, your module can now be debugged. > > In order to do that, we need to launch Rocky and attach the debugger > in the Solver. ![undefined](https://developer.ansys.com/sites/default/files/inline-images/debugrockymodules_img4_0.png) 7. Create a folder inside the module folder and name it ***.vscode****(with a dot in the name).* 8. Go to the **Run and Debug** in the left panel and click on **create a launch.json file**. 9. Select the first option you see, for example, *Edge: Launch*. 10. Delete the content of the configurations list and click on **Add Configuration**. 11. Choose the option C/C++: (Windows) Start/Launch. It should look like this: ```json { "version": "0.2.0", "configurations": [ { "name": "(Windows) Attach", "type": "cppvsdbg", "request": "attach" }, { "name": "(Windows) Launch", "type": "cppvsdbg", "request": "launch", "program": "Indlude the path to the Rocky executable", "args": [], "stopAtEntry": false, "cwd": "${fileDirname}", "environment": [], "console": "externalTerminal" } ] } ``` 12. Now we just need to supply the path for the **Rocky Solver** and the solver arguments. To make it easier to understand, you can open the simulation log file of any Rocky project, found under the simulation folder and named as rocky\_simulation.rocky20.log. Right after the file header, you will see the command line that was used to launch the Rocky Solver: ```plaintext Command line: C:\Program Files\ESSS\Rocky 2022 R1\bin\RockySolver.exe --rcy-file=C:\Users\vdaroz\Documents\Delete\freeze_roi.rocky.files\simulation/rocky_simulation.rocky20 --license=C:\Users\vdaroz\AppData\Roaming\Rocky\license.lic --ncpus=4 ``` 13. We just need to copy that information to the **launch.json file**. It should look like: ![undefined](https://developer.ansys.com/sites/default/files/inline-images/debugrockymodules_img5_0.png) Have in mind that we have changed the argument --ncpus to 1 instead of 4. We recommend debugging using only 1 CPU. Debugging in parallel is much more complicated. 14. As soon as you have the **launch.json file** set up, you just need to create the breakpoints wherever you need, go to **Run and Debug** in the left panel in **VS Code,** and click the launch button. If it works, you will see everything working properly. With practice, debugging becomes not just a troubleshooting step, but a key part of writing robust **Rocky Custom Modules**, enabling detailed logging and using tools like Visual Studio, you can identify and resolve issues more efficiently. Keep iterating, stay curious, and do not hesitate to dive deeper into **Solver SDK** examples in the [**Rocky Solver SDK Manual**](https://developer.ansys.com/docs/rocky).