callback function from c# to c++

Question

Sam Hobbs · Answer

Can you provide details of the requirements? Since you say callback I assume that a C++ program is calling a C# program that you want to call C++ from. How does the C++ program call the C# program? Is the C++ program managed C++? I have written the following articles that might be relevant but I need more information to be able to be specific. Native Windows Dynamic Link Libraries (DLLs) https://www.c-sharpcorner.com/UploadFile/SamTomato/native-windows-dynamic-link-libraries-dlls Managed C++ Wrapper For Unmanaged Code https://www.c-sharpcorner.com/UploadFile/SamTomato/managed-cpp-wrapper-for-unmanaged-code

Simran Verma · Answer

To call a C++ function from C#, you can use Platform Invocation Services (P/Invoke). Here's a basic example demonstrating how to achieve this: Let's say you have a C++ function that you want to call from C#: // C++ code #include extern "C" { typedef void(*CallbackFunc)(int); __declspec(dllexport) void RegisterCallback(CallbackFunc callback) { // Invoke the callback function with some value callback(42); } } And here's how you would call this C++ function from C#: // C# code using System; using System.Runtime.InteropServices; class Program { // Define the delegate to match the callback function signature delegate void CallbackDelegate(int value); // Import the C++ function [DllImport("YourCppLibrary.dll")] private static extern void RegisterCallback(CallbackDelegate callback); // Define the callback function static void MyCallback(int value) { Console.WriteLine($"Callback received value: {value}"); } static void Main() { // Call the C++ function and pass the callback function RegisterCallback(MyCallback); Console.WriteLine("Press any key to exit..."); Console.ReadKey(); } } In this example: We define a C++ function RegisterCallback that takes a function pointer as an argument. In the C# code, we define a delegate CallbackDelegate to match the signature of the callback function expected by the C++ function. We import the RegisterCallback function from the C++ DLL using the DllImport attribute. We define the callback function MyCallback in C#, and pass it as an argument when calling RegisterCallback . When the C++ function RegisterCallback is invoked, it calls back the provided function pointer, which is the C# function MyCallback , passing the value 42 . Finally, the MyCallback function in C# is executed, printing the received value. Remember to replace "YourCppLibrary.dll" with the actual name of your compiled C++ DLL. Additionally, ensure that the C++ function is marked for export using __declspec(dllexport) or appropriate methods based on your compiler.