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How Can I Access a C DLL Class with Member Variables and Non-Static Methods from C#?
How Can I Access a C DLL Class with Member Variables and Non-Static Methods from C#?
Dec 28, 2024 pm 09:49 PM
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:
- Create non-member functions for each class member function, calling into the member functions.
- 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#.
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