What is P/Invoke?

💡 Concept: P/Invoke in C#

P/Invoke (Platform Invocation) allows managed C# code to call functions exported from unmanaged libraries such as Windows DLLs.

📘 Quick Intro

P/Invoke bridges managed and unmanaged code by describing the method signatures and marshaling data appropriately.

🧠 Analogy

Think of P/Invoke as a translator allowing two people who speak different languages to communicate.

🔧 Technical Explanation

🛠 Uses [DllImport] attribute to declare external methods.
🔄 Marshals data types between managed and unmanaged memory.
⚠️ Requires careful handling of memory and types to avoid errors.
📚 Supports calling Windows API, legacy libraries, and custom unmanaged DLLs.
🔐 Security considerations must be addressed.

🎯 Use Cases

✅ Accessing Windows native APIs.
✅ Reusing legacy unmanaged libraries.
✅ Performance-critical operations in native code.
✅ Interfacing with hardware or system resources.

💻 Code Example


using System.Runtime.InteropServices;

public class NativeMethods {
    [DllImport("user32.dll", CharSet = CharSet.Auto)]
    public static extern int MessageBox(IntPtr hWnd, string text, string caption, uint type);
}

public class Program {
    public static void Main() {
        NativeMethods.MessageBox(IntPtr.Zero, "Hello from P/Invoke!", "Example", 0);
    }
}

❓ Interview Q&A

Q1: What does P/Invoke stand for?
A: Platform Invocation.

Q2: What attribute is used to import DLL functions?
A: [DllImport].

Q3: How is data marshaled?
A: Automatically based on declared signatures.

Q4: Can P/Invoke cause errors?
A: Yes, due to incorrect signatures or memory issues.

Q5: Is P/Invoke platform-dependent?
A: Mainly Windows, but .NET Core supports others.

Q6: Can P/Invoke call unmanaged COM objects?
A: Yes, with COM interop.

Q7: What namespaces are involved?
A: System.Runtime.InteropServices.

Q8: Does P/Invoke support callbacks?
A: Yes, with delegates.

Q9: How to handle string parameters?
A: Specify CharSet and marshaling.

Q10: What is the risk of P/Invoke?
A: Possible security and stability issues.

📝 MCQs

Q1. What does P/Invoke stand for?

Platform Invocation
Platform Integration
Platform Interchange
Platform Inspection

Q2. Which attribute is used for DLL imports?

[DllImport]
[MarshalAs]
[UnmanagedFunctionPointer]
[ComImport]

Q3. Can P/Invoke cause errors?

No
Yes
Sometimes
Never

Q4. Is P/Invoke platform-dependent?

Linux only
Mainly Windows
Mac only
Cross-platform

Q5. Can P/Invoke call COM objects?

No
Yes
Sometimes
Never

Q6. What namespace is used?

System.IO
System.Runtime.InteropServices
System.Net
System.Data

Q7. Does P/Invoke support callbacks?

No
Yes
Sometimes
Never

Q8. How to handle strings in P/Invoke?

Ignore
Specify CharSet
Use UTF8Encoding
Don't use strings

Q9. What is the risk of P/Invoke?

No risk
Security and stability
Memory leaks only
Performance only

Q10. How is data marshaled?

Manually
Automatically
Not at all
Sometimes

💡 Bonus Insight

P/Invoke extends .NET capabilities but requires attention to detail and security practices.

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