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Learn effective methods to call managed .NET code from unmanaged C++ without COM wrappers, using C++/CLI and function pointers.
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How to Efficiently Call Managed Code from Unmanaged Code in C++

In the world of software development, integrating different types of code can often present challenges. One frequent scenario developers encounter is the need to call managed .NET code from unmanaged C++. This task can be particularly daunting because of the differences in how these two environments operate. If your process entry point is .NET based and you're aiming for a way to access individual static methods of managed classes, you might find tracking down a concise method to achieve that a bit complicated.

In this guide, we will explore strategies for calling managed code from unmanaged C++, focusing specifically on two effective methods: using C++/CLI wrappers and marshaling function pointers.

Understanding the Problem

Before diving into the solutions, let's clarify the context:

Managed Code: This refers to code executed by the .NET runtime known as the Common Language Runtime (CLR). It provides services like garbage collection and exception handling.

Unmanaged Code: This is typically native code, such as native C++, that runs directly on the operating system without the CLR's management.

COM Wrappers: Traditionally, developers could access .NET functionality from unmanaged code through COM. However, in scenarios demanding direct access to specific methods without overhead, this approach might not be efficient.

Solutions for Calling Managed Code from Unmanaged Code

1. Using C++/CLI Wrapper

One of the simplest ways to bridge managed and unmanaged code is through C++/CLI, a language specification created specifically for this purpose. Here’s how to do it effectively:

Steps to Create a C++/CLI Wrapper:

Create a C++/CLI Project: Start by setting up a new project in Visual Studio and selecting the C++/CLI project type.

Reference Your .NET Assembly: Add a reference to the .NET assembly whose methods you want to call.

Write the Wrapper:

Create public ref classes that will act as the wrapper for the managed code.

Use __declspec(dllexport) to allow methods to be exported for use in unmanaged code.

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Compile the Project: This will generate a DLL that can be loaded by your unmanaged application.

2. Marshaling Function Pointers

If you have more control over the invocation of your unmanaged code, marshaling function pointers to your .NET methods can be an excellent way to achieve tight integration without needing a full COM interface.

Steps to Marshal Function Pointers:

Define a Delegate in C++/CLI: Create a delegate that matches the signature of the static methods in your managed code.

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Create an Instance of the Delegate: In your C++/CLI wrapper, you can create an instance of this delegate and pass it to your unmanaged code.

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Pass the Function Pointer: You can now get a function pointer from this delegate and pass it to your unmanaged code.

Conclusion

Choosing the right method to call managed code from unmanaged code largely depends on your specific requirements and control over the code. C++/CLI wrappers offer a straightforward and clean way to access managed features, especially when focusing on accessing static methods. On the other hand, if performance and direct method calls are of utmost importance, marshaling function pointers is an effective solution without the complexities of COM.

By utilizing these methods, you can seamlessly connect your unmanaged applications to the richness of .NET, enhancing functionality while keeping your engineering streamlined.

Whether you choose to create a wrapper or marshal function pointers, the integration of managed and unmanaged code can potentiate your projects, unlocking new pos