CODEWITHSUNDEEP
c#c++interop
user1946771
user1946771

Reputation:

Call from C# to C++ fails to pass parameters correctly

I have a very basic call from C# to C++. The function call takes three parameters:

extern "C" int CLIENT_API example(const char, char * const, const unsigned int);

The C# code imports that function as:

[DllImport("my.dll", CallingConvention = CallingConvention.Cdecl)]
public static extern int example(in sbyte id, byte[] buffer, in uint bufferSize);

When I call the function from C# like this:

uint bufferSize = 400;
byte[] buffer = new byte[bufferSize];
example(0, buffer, bufferSize);

I log on the C++ size variant values for both id and bufferSize (every run has different values for those two variables). What am I doing wrong? I have other interop functions that pass pointers and strings to my C++ DLL and they aren't having any issues. It seems like it just happens with the more primitive types of byte and uint.

Upvotes: 1

Views: 225

Answers (1)

madreflection
madreflection

Reputation: 4937

The in modifier makes the argument a read-only ref argument. It's not the same as the [In] attribute, which is a marshalling hint.

You're passing 0 and bufferSize, and C# is taking their addresses (the literal 0 by way of a temporary variable) and passing those.

You're getting varying values because the address is different each time.

Remove the in modifiers so that C# passes those values rather than addresses.

Upvotes: 2

Related Questions