What causes this error in a C++ app calling a C# DLL?

Question

I haven't programmed in C++ since before .Net -- for Windows I use C# and .Net now.

I have a C# .Net DLL that I call from other C# programs with no problems. But I have a customer who wants to call it from C++ so I'm writing a practice app to see how it's done. NB this is C++/CLI ie, it's a managed, CLI-CIL-CLR app.

In my C# program I add my DLL as a reference then in my code I have a using statement and then instantiate it . . .

    using ScannerBeam;
    . . . 

    CScannerBeam SB = new CScannerBeam();

. . . works a treat, no problems. But in C++ I also add the DLL as a reference and do a

    using namespace ScannerBeam;
    . . . 

    CScannerBeam SB = gcnew CScannerBeam();

...and I get an error . . .

Error 1 error C3673: 'ScannerBeam::CScannerBeam' : class does not have a copy-constructor

Why does it need a copy constructor when C# doesn't? Does it need a deep copy or just a shallow one? Any other gotchas I need to know calling a C# DLL from (managed/CLI/CLR) C++?

Answer 1

引用类需要refptr，CScannerBeam ^表示C ++-CLI中的ref_ptr。

Answer 2

gcnew evaluates to a tracking handle, of type CScannerBeam^

Your code is not much different from:

std::string s = new std::string();

which is also an error, the right side is a pointer and the left side isn't.

Just like native C++, use either

CScannerBeam SB; // creates an object with stack semantics
                 // it will be disposed at end the of the scope
func(sb.member);

or

CScannerBeam^ pSB = gcnew ScannerBeam(); // get handle to object on managed heap
                                         // it has dynamic lifetime and will live as
                                         // long as the .NET garbage collector can reach it
func(pSB->member);