Unit testing Inconsistent dll linkage leads to compilation error - c++

Question

New to c++ and trying to test a dll but keep getting
warning C4273: 'CRootFinder::SquareRoot' : inconsistent dll linkage
RootFinder.h
#ifdef MY_EXPORTS
#define API _declspec(dllexport)
#else
#define API _declspec(dllimport)
#endif
class API CRootFinder {
public:
CRootFinder(void);
double SquareRoot(double v);
};
RootFinder.cpp
#include "stdafx.h"
#include "RootFinder.h"
double CRootFinder::SquareRoot(double v)
{
return 0.0;
}
Builds but gets warning above.
Added reference to dll to unit test project
unittest1.cpp
#include "stdafx.h"
#include "CppUnitTest.h"
#include "../c source/RootFinder.h"
using namespace Microsoft::VisualStudio::CppUnitTestFramework;
namespace Tests
{
TEST_CLASS(UnitTest1)
{
public:
TEST_METHOD(TestMethod1)
{
CRootFinder rooter;
Assert::AreEqual(
// Expected value:
0.0,
// Actual value:
rooter.SquareRoot(0.0),
// Tolerance:
0.01,
// Message:
L"Basic test failed",
// Line number - used if there is no PDB file:
LINE_INFO());
}
};
}
Won't build
Error 2 error LNK2019: unresolved external symbol "__declspec(dllimport) public: __thiscall
CRootFinder::CRootFinder(void)" (__imp_??0CRootFinder##QAE#XZ)
referenced in function "public: void __thiscall
Tests::UnitTest1::TestMethod1(void)"
(?TestMethod1#UnitTest1#Tests##QAEXXZ)

Answer 1

Compile dll with MY_EXPORTS preprocessor marco. Add use it in test without MY_EXPORTS definition macro.
In Visual Studio you can do that: Project right click->Propertis->C/C++->Preprocessor->Preprocessor Definitions, just add MY_EXPORTS to the list for dll project, and leave that list without MY_EXPORTS for test project.
And you need define constructor CRootFinder() in RootFinder.cpp.