C++/CLI Windows Forms - creating custom DLL library

Question

Today I wanted to make my own dynamic library. I am using VC++ 2010. Tried to apply a console example (from http://msdn.microsoft.com/en-us/library/ms235636%28v=vs.80%29.aspx) but I keep failing. Here are steps I follow:

Create Win32 project and choose Empty Project, DLL from wizard,

Create a header with

// FILE: bday.h
#ifndef BDAY_H_
#define BDAY_H_

#ifdef BUILD_DLL
#define PORT_DLL __declspec(dllexport)
#else
#define PORT_DLL __declspec(dllimport)
#endif

namespace Tests
{
    public class BDay
    {
    public:
        static PORT_DLL double Foo(double);
    };
};
#endif

Create a .cpp to implement that class,
Build this project which is successful.

Then I go with

Create Windows Forms project, add reference to the previously created .dll,
Include bday.h from the previous project.
Define BUILD_DLL constant,
Add a button which calls Tests::BDay::Foo upon clicking.

Building this project gives me

1>CoreResGen:
1>  Processing resource file "Form1.resX" into "Debug\generatory2.Form1.resources".
1>generatory2.obj : error LNK2028: unresolved token (0A00000F) "public: static double __cdecl Tests::BDay::Foo(double)" (?Foo@BDay@Tests@@$$FSANN@Z) referenced in function "private: void __clrcall generatory2::Form1::button4_Click(class System::Object ^,class System::EventArgs ^)" (?button4_Click@Form1@generatory2@@$$FA$AAMXP$AAVObject@System@@P$AAVEventArgs@4@@Z)
1>generatory2.obj : error LNK2019: unresolved external symbol "public: static double __cdecl Tests::BDay::Foo(double)" (?Foo@BDay@Tests@@$$FSANN@Z) referenced in function "private: void __clrcall generatory2::Form1::button4_Click(class System::Object ^,class System::EventArgs ^)" (?button4_Click@Form1@generatory2@@$$FA$AAMXP$AAVObject@System@@P$AAVEventArgs@4@@Z)
1>C:\Users\Patryk\Documents\Visual Studio 2010\Projects\generatory2\Debug\generatory2.exe : fatal error LNK1120: 2 unresolved externals

There must me something that I'm doing wrong, can you point out where the error is?

Yochai Timmer · Accepted Answer · 2013-07-27 19:36:48Z

2

If you want to reference it as .Net class and method, you need to make it so.
The dll export/import is for unmanaged code. (Native c++ in your case).

In a c++ project you'd have to compile the .dll with a matching .lib file, and then link the lib file so the function can be found.

In a .Net library on the other hand, you just need to reference the dll. But for that it need to be compiled as a .Net library.

Compile the dll with the /CLR flag. And make the class a reference .Net class:

namespace Tests
{
    public ref class BDay
    {
    public:
        static double Foo(double);
    };
};

You don't need the declspec export and import for .Net

answered Jul 27, 2013 at 19:36

Yochai Timmer

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1 Comment

patryk Over a year ago

This worked as expected. Thank you for this simple and clear explanation

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