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Discover how to effectively call an external C script that uses GLPK within Modelica, solving common linker errors with practical steps.
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Solving Linker Errors When Integrating C Code with Modelica using GLPK

Integrating C code with Modelica can sometimes lead to frustrating linker errors, particularly when external libraries like GLPK (GNU Linear Programming Kit) are involved. If you have a working C script but encounter issues when linking it with your Modelica model, you're not alone. In this post, we will walk you through a common scenario: calling a C script that uses an external library, addressing the specific linker errors that may arise, and providing a step-by-step solution to resolve these issues.

Understanding the Problem

You may find yourself with a C code working fine in standalone mode using a special linker command such as:

[[See Video to Reveal this Text or Code Snippet]]

However, when you attempt to link this C code efficiently within your Modelica model, you get errors like:

[[See Video to Reveal this Text or Code Snippet]]

This specific error indicates that the Modelica environment is unable to find the necessary reference to the GLPK library, suggesting that the linking process is not set up correctly. Let's explore how to set it up properly.

Step-by-Step Solution

Compile the GLPK Header File: First, ensure that the GLPK header file is compiled properly. You can do this using the following command:

[[See Video to Reveal this Text or Code Snippet]]

This command generates an object file that can be linked later.

Create a Shared Library from Your C Code: Next, convert your C file (let's say st_linprog.c) into a shared library. You can do this by running:

[[See Video to Reveal this Text or Code Snippet]]

This command compiles st_linprog.c and links it against the GLPK library, producing the liblinprog.so shared library.

Annotate Your Modelica Code: In your Modelica model file (let's say function.mo), you need to add an annotation that specifies the libraries you are using. Add the following lines:

[[See Video to Reveal this Text or Code Snippet]]

This annotation informs Modelica of the libraries it needs to link against and their location.

Conclusion

By following these steps, you can resolve common linker errors associated with integrating C code and external libraries, such as GLPK, in Modelica. Compiling the GLPK header, creating a shared library from your C code, and properly annotating your Modelica model are crucial steps that will help eliminate those pesky linker errors.

If you have encountered more elegant approaches or have any additional insights to share, feel free to contribute. Happy coding and good luck with your Modelica models!

Cheers,
Phil