CODEWITHSUNDEEP
c++c++-cliwrapperlinker-errors
0699
0699

Reputation: 250

C++\CLI LNK Error 2019 & 2028 with Included .h and .lib (Linker finds those Files) [Wrapper]

I have a problem with this code, writing a wrapper function from an existing .lib (CryptoLib.lib):

mycode.ccp

#include "stdafx.h"
#pragma managed(push, off)
#include "CryptoLib.h"
#pragma comment (lib, "CryptoLib.lib")
#pragma managed(pop)

using namespace System;//This is a C++-CLI project.

__declspec(dllexport) void Encrypt(unsigned char *Data, unsigned char *RandomNr)
{
   CryptoLib_Encrypt(Data, RandomNr);
}

cryptolib.h

#ifndef _CRYPTOLIB_H_
#define _CRYPTOLIB_H_

#define PUBLIC
//This procedure is written in c++ code
extern void CryptoLib_Encrypt(unsigned char *Data, unsigned char *RandomNr);

#endif /* _CRYPTOLIB_H_ */

I have linked the cryptolib.h and the cryptolib, but i get still the "unresolved token Cryptolib_Encrypt" and the "unresolved external symbol Cryptolib_Encrypt" Errors.

Can anyone tell me why?

Thanks for helping

Exact Error-messages:

error LNK2028: unresolved token (0A000006) "void __cdecl CryptoLib_Encrypt(unsigned char *,unsigned char *)" (?CryptoLib_Encrypt@@$$FYAXPAE0@Z) referenced in function "void __cdecl Encrypt(unsigned char *,unsigned char *)" (?Encrypt@@$$FYAXPAE0@Z)
error LNK2019: unresolved external symbol "void __cdecl CryptoLib_Encrypt(unsigned char *,unsigned char *)" (?CryptoLib_Encrypt@@$$FYAXPAE0@Z) referenced in function "void __cdecl Encrypt(unsigned char *,unsigned char *)" (?Encrypt@@$$FYAXPAE0@Z)


error LNK1120: 2 unresolved externals

The Dumpbin.exe /exports comand line returns just Dumpbin.exe /exports

But i still added the C/C++ Additional Include Directory in Configuration Properties/"C/C++"/General and the Additional Dependencies (Cryptolib.lib) in Configuation Properties/Linker/Input

Upvotes: 3

Views: 3265

Answers (1)

Hans Passant
Hans Passant

Reputation: 941455

#pragma once
#pragma comment (lib, "CryptoLib.lib")
#include "stdafx.h"

This is wrong. The compiler will go looking for the stdafx.h #include directive and ignores anything it finds before that. So it will completely ignore your #pragma comment directive. The linker will therefore not link CryptoLib.lib and you'll indeed get this linker error. Using #pragma once in a .cpp file does not make sense.

Another problem is that you appear to compile this code with /clr in effect, we can tell from the using statement. The compiler cannot tell that your function is a __cdecl function, it will assume the default and that's __clrcall when managed code compilation is enabled. You have to be explicit about it, like this: 

#include "stdafx.h"          // First line in file!
#pragma managed(push, off)
#include "CryptoLib.h"
#pragma comment (lib, "CryptoLib.lib")
#pragma managed(pop)

There's yet another possible problem with the function declaration, it isn't clear whether that function was compiled with a C compiler or a C++ compiler. A C++ compiler will decorate the function name. If it was actually compiled with a C compiler then you have to tell the compiler about that:

#ifndef _CRYPTOLIB_H_
#define _CRYPTOLIB_H_

#ifdef __cplusplus
extern "C" {
#endif

void __cdecl CryptoLib_Encrypt(unsigned char *Data, unsigned char *RandomNr);

#ifdef __cplusplus
}
#endif

#endif /* _CRYPTOLIB_H_ */

Note the usage of extern "C", it disables name decoration. If you cannot or should not edit this header file then you can cram the extern "C" {} in your .cpp file, surrounding the #include.

If you still have trouble then post the exact linker error message as well what you see when you run Dumpbin.exe /exports on the DLL from the Visual Studio Command Prompt.

Upvotes: 5

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