How Can I Access a C DLL Class with Member Variables and Non-Static Methods from C#?

Accessing a C DLL Class in C# Code

Problem:

Using P/Invoke to access functions in a C DLL with member variables and non-static methods requires creating instances of the defining class. How can access be gained to this class?

Answer:

Directly using a C class in C# is not possible. Instead, follow these steps:

1. Create non-member functions for each class member function, calling into the member functions.
2. Use P/Invoke to expose these non-member functions to C#.

Example:

class Foo {
public:
  int Bar();
};
extern "C" Foo* Foo_Create() { return new Foo(); }
extern "C" int Foo_Bar(Foo* pFoo) { return pFoo->Bar(); }
extern "C" void Foo_Delete(Foo* pFoo) { delete pFoo; }

In C#:

[DllImport("Foo.dll")]
public static extern IntPtr Foo_Create();

[DllImport("Foo.dll")]
public static extern int Foo_Bar(IntPtr value);

[DllImport("Foo.dll")]
public static extern void Foo_Delete(IntPtr value);

Wrapper Class:

To simplify usage, wrap the IntPtr pointer into a C# wrapper class:

public class FooWrapper
{
  private IntPtr _foo;

  public FooWrapper()
  {
    _foo = Foo_Create();
  }

  public int Bar()
  {
    return Foo_Bar(_foo);
  }

  public void Dispose()
  {
    Foo_Delete(_foo);
  }
}

Alternative Approach:

If unable to modify the original DLL, create an intermediate DLL that wraps the original DLL and exposes the wrapped class to C#.

The above is the detailed content of How Can I Access a C DLL Class with Member Variables and Non-Static Methods from C#?. For more information, please follow other related articles on the PHP Chinese website!