How do I link a C++/CLI library to C++ application - c++

Question

I made a C++/CLI wrapper for using a C# DLL in a C++ application. I used Visual Studio to manage the projects and manage the dependencies, and I got it to work that way.
But I can't get it to work when I use CMake to link the library that Visual Studio built for me.
cmake_minimum_required (VERSION 3.12)
project(playground CXX)
SET(CMAKE_CXX_STANDARD 17)
set(PLAYGROUND_SOURCE_DIR ${CCMAKE_CURRENT_SOURCE_DIR})
set(PLAYGROUND_BINARY_DIR ${CMAKE_CURRENT_BINARY_DIR})
set(PLAYGROUND_SRC
main.cpp)
add_executable(Playground ${PLAYGROUND_SRC} ${PLAYGROUND_HDR})
find_library(comm_dll CommWrapper Lib/CommDLL)
target_link_libraries(Playground PUBLIC
${comm_dll}
)
Using this method gets me an "unresolved external symbol error". I have the .dll, .lib and .h file in the same folder.

Answer 1

As Hans Passant already stated: you must compile your C++/CLI code as Dynamic Library in order to be able to consume it from an unmanaged application. CLI/Managed code cannot run from/cannot reside in static libraries. If you change the C++/CLI library target from Static library to Dynamic library you'll be able to compile successfully your unmanaged C++ application.
One thought from my side: I think you'll be better if you use mixed mode C++/CLI DLLs to consume the managed functionality - you'll be able to free your consumer application completely from referencing the CLR.
The Header of such mixed mode Wrapper for your Element class would look like this:
#pragma once
#pragma unmanaged
#if defined(LIB_EXPORT)
#define DECLSPEC_CLASS __declspec(dllexport)
#else
#define DECLSPEC_CLASS __declspec(dllimport)
#endif
class ElementWrapperPrivate;
class __declspec(dllexport) ElementWrapper
{
private:
ElementWrapperPrivate* helper;
public:
ElementWrapper();
~ElementWrapper();
public:
void ExecuteCommand();
};
And the implementation would look like this:
#include "ElementWrapper.h"
#pragma managed
#include "Element.h"
#include <msclr\auto_gcroot.h>
using namespace System::Runtime::InteropServices;
class ElementWrapperPrivate
{
public:
msclr::auto_gcroot<Element^> elementInst; // For Managed-to-Unmanaged marshalling
};
ElementWrapper::ElementWrapper()
{
helper = new ElementWrapperPrivate();
helper->elementInst = gcnew Element();
}
ElementWrapper::~ElementWrapper()
{
delete helper;
}
void ElementWrapper::ExecuteCommand()
{
helper->elementInst->ExecuteCommand();
}
Then just compile your Element.cpp + ElementWrapper.cpp to a DLL and use the ElementWrapper.h in your unmanaged applications.