The Four P&#39;s... A four part P/Invoke tutorial series

Tuesday, June 12, 2012

P/Invoke is a way of calling C/C++ functions from a .NET program. It’s very easy to use. This article will cover the basics of using P/Invoke.

Note: This tutorial will focus on Windows and thus use Visual Studio. If you’re developing on another platform or with another IDE, adopting the things in this article should be easy enough.

Project Structure

For this tutorial, we need a small project structure containing two projects:

NativeLib : a C++ library project

PInvokeTest : a C# console project

Simple P/Invoke

Troubleshooting

Unable to load DLL

Stack Imbalance

Portability

C++/CLI

P/Invoke Tutorial: Passing strings (Part 2)

In the previous tutorial we passed a single string to a native C/C++ function by using P/Invoke.

This function was defined like this:
// C++
void print_line(const char* str);
// C#
[DllImport("NativeLib.dll")]
private static extern void print_line(string str);
However, there exists a hidden pitfall here:

What happens when the user passes a non-ASCII character to this function?

ASCII and Unicode: A Historical Overview

P/Invoke String Conversions

P/Invoke Tutorial: Passing parameters (Part 3)

P/Invoke tries to make your life easier by automatically converting (“marshalling”) data types from managed code to native code and the other way around.

Marshalling Primitive Data Types

Marshalling Strings

Marshalling Arrays

Marshalling Objects

Marshalling Structs

Marshalling Arbitrary Pointers

P/Invoke Tutorial: Pinning (Part 4)

Sometimes a C/C++ function needs to store data you pass to it for later reference. If such data is a managed object (like a string or class) you need to make sure that the garbage collector doesn’t delete it while it’s still in use/still stored in the native code.

That’s what pinning is for. It prevents the garbage collector from deleting and moving the object.

Pinning an Object

Passing a Pinned Object

Pinning and Passing Strings

Verifying the Pinned Object is passed