unresolved external symbol while using a library - syntax-error

Question

i have a header file named NetworkInterfaceInfoProvider.h.
in this header file i declare a class as follow:
#ifndef INETWORK_INTERFACE_INFO_PROVIDER_H
#define INETWORK_INTERFACE_INFO_PROVIDER_H
#pragma once
/*#include "stdafx.h"*/
#include "IConfig.h"
#include "NetworkAddapterAddresses.h"
#include "InstaledAddapters.h"
namespace IRNetwork
{
class CLASS_DECLSPEC INet;
struct CLASS_DECLSPEC GenericIPAddress;
/*
* provide information about all network interface related adapters such as installed interfaces , addresses , best routes and ...
* TO DO: implement Other OS's
*/
class CLASS_DECLSPEC INetworkInterfaceInfoProvider
{
public:
INetworkInterfaceInfoProvider(void);
~INetworkInterfaceInfoProvider(void);
int32_t GetBestRouteTo(char* destIp,uint16_t port,ip_t *ip);
int32_t GetBestRouteTo(GenericIPAddress* ip);
private:
INet* snet;
};
}
#endif
when i want to use it in my console application i got following linker error
*note: the library of above code has been linked to my console application.
CLASS_DECLSPEC is dll import/export definition*
error LNK2019: unresolved external symbol "__declspec(dllimport)
public: int __thiscall
IRNetwork::INetworkInterfaceInfoProvider::GetBestRouteTo(char
,unsigned short,char ()[65])" (_imp?GetBestRouteTo#INetworkInterfaceInfoProvider#IRNetwork##QAEHPADGPAY0EB#D#Z)
referenced in function "void __cdecl test_adapters(void)"
(?test_adapters##YAXXZ) testDhcpv4.obj testDhcpv4
what is wrong here?

Answer 1

Hmm. From the error I would say importing looks good. So maybe there was an error while exporting. Assuming you are using Visual Studio, you can use dumpbin to check if your dll is exporting correctly:
Open the Visual Studio Command Prompt (available from the windows start menu) and type
dumpbin /EXPORTS yourlib.dll
Then you should see our export, something like (dump from one of my dlls):
...
170 A9 00108120 ??1AbstractParam#param#core#megamol##UAE#XZ = ??1BoolParam#param#core#megamol##UAE#XZ (public: virtual __thiscall megamol::core::param::BoolParam::~BoolParam(void))
...
If the function your are calling is not listed, you should doublecheck if your dllexport is set correctly while building your dll.
If the function is listed, but looks different, you should check for the calling conventions to be the same for your application and your dll.
If the function is listed and the name looks identical to what the error message says, doublecheck if you are linking the import library of the dll correctly.
Also check if the runtime-configuration is the same for your application and your dll (e.g. Multi-Threaded-Dll or Multi-Threaded-Debug-Dll).