How do you call unmanaged code in C#?
💡 Concept: Calling Unmanaged Code from C#
Unmanaged code refers to native code executed outside the .NET runtime. Calling it from C# is done via Platform Invocation Services (P/Invoke).
📘 Quick Intro
P/Invoke allows managed code to call functions exported from unmanaged DLLs.
🧠 Analogy
Like placing an international phone call through a gateway that translates protocols.
🔧 Technical Explanation
- Use DllImport attribute to specify DLL and function signatures.
- Handle data marshaling between managed and unmanaged memory.
- Supports calling C, C++, and Win32 APIs.
- Careful with memory management to avoid leaks and crashes.
- Example: calling MessageBox from user32.dll.
🎯 Use Cases
- ✅ Accessing legacy native libraries.
- ✅ Calling OS-level APIs.
- ✅ Performance critical code sections.
- ✅ Integrating with hardware or external devices.
💻 Code Example
using System.Runtime.InteropServices;
class Program {
[DllImport(""user32.dll"", CharSet = CharSet.Unicode)]
public static extern int MessageBox(IntPtr hWnd, string text, string caption, int options);
static void Main() {
MessageBox(IntPtr.Zero, ""Hello from unmanaged code!"", ""P/Invoke Example"", 0);
}
}
❓ Interview Q&A
Q1: What is unmanaged code?
A: Code not managed by the CLR.
Q2: What is P/Invoke?
A: Platform Invocation to call unmanaged DLL functions.
Q3: How do you specify the DLL?
A: Using DllImport attribute.
Q4: What are marshaling concerns?
A: Converting data between managed and unmanaged memory.
Q5: Can you call C++ code?
A: Yes, if exposed via C-style DLL exports.
Q6: Is memory management automatic?
A: No, must be handled carefully.
Q7: Can P/Invoke cause crashes?
A: Yes, if used incorrectly.
Q8: Is P/Invoke supported on all .NET platforms?
A: Mostly, but some restrictions exist.
Q9: Alternatives to P/Invoke?
A: COM Interop, C++/CLI.
Q10: Why call unmanaged code?
A: For legacy or performance reasons.
📝 MCQs
Q1. What is unmanaged code?
- Code outside CLR management
- Managed code
- C# code
- Java code
Q2. What is P/Invoke?
- Calling managed code
- Calling unmanaged DLLs
- Debugging
- Profiling
Q3. How to specify DLL?
- DllImport attribute
- Marshal class
- Namespace
- Assembly info
Q4. What is marshaling?
- Memory allocation
- Data conversion
- Thread management
- Garbage collection
Q5. Can P/Invoke call C++?
- No
- Yes
- Sometimes
- Rarely
Q6. Is memory management automatic?
- Yes
- No
- Sometimes
- Rarely
Q7. Can P/Invoke cause crashes?
- No
- Yes
- Maybe
- Never
Q8. Is P/Invoke on all .NET platforms?
- No
- Mostly
- Yes
- Sometimes
Q9. Alternatives to P/Invoke?
- COM Interop
- Reflection
- Serialization
- Attributes
Q10. Why call unmanaged code?
- For fun
- Legacy or performance
- Testing
- Debugging
💡 Bonus Insight
Calling unmanaged code bridges legacy native libraries with modern .NET applications, enabling powerful integrations.
📄 PDF Download
Need a handy summary for your notes? Download this topic as a PDF!