how to solve "dllmain.obj : error LNK2019: unresolved external symbol "public" error while making a dll project? :     1>     Creating library C:\Users\pars\Desktop\example\FEneohookean\Debug\FEneohookean.lib and object C:\Users\pars\Desktop\example\FEneohookean\Debug\FEneohookean.exp
    1>dllmain.obj : error LNK2019: unresolved external symbol "public: virtual __thiscall FECoreFactory::~FECoreFactory(void)" (??1FECoreFactory@@UAE@XZ) referenced in function __
    1>dllmain.obj : error LNK2019: unresolved external symbol "public: void __thiscall FECoreKernel::RegisterClass(class FECoreFactory *)" (?RegisterClass@FECoreKernel@@QAEXPAVFECoreFactory@@@Z) referenced in function "public: __thiscall FERegisterClass_T<class FENeoHookeanPI>::FERegisterClass_T<class FENeoHookeanPI>(unsigned int,char const *)" (??0?$FERegisterClass_T@VFENeoHookeanPI@@@@QAE@IPBD@Z)
    1>dllmain.obj : error LNK2019: unresolved external symbol "public: static class FECoreKernel & __cdecl FECoreKernel::GetInstance(void)" (?GetInstance@FECoreKernel@@SAAAV1@XZ) referenced in function "public: __thiscall FERegisterClass_T<class FENeoHookeanPI>::FERegisterClass_T<class FENeoHookeanPI>(unsigned int,char const *)" (??0?$FERegisterClass_T@VFENeoHookeanPI@@@@QAE@IPBD@Z)
    1>dllmain.obj : error LNK2019: unresolved external symbol "public: __thiscall FECoreFactory::FECoreFactory(unsigned int,char const *)" (??0FECoreFactory@@QAE@IPBD@Z) referenced in function "public: __thiscall FERegisterClass_T<class FENeoHookeanPI>::FERegisterClass_T<class FENeoHookeanPI>(unsigned int,char const *)" (??0?$FERegisterClass_T@VFENeoHookeanPI@@@@QAE@IPBD@Z)
    1>dllmain.obj : error LNK2019: unresolved external symbol "public: __thiscall FEElasticMaterial::FEElasticMaterial(class FEModel *)" (??0FEElasticMaterial@@QAE@PAVFEModel@@@Z) referenced in function "public: __thiscall FENeoHookeanPI::FENeoHookeanPI(class FEModel *)" (??0FENeoHookeanPI@@QAE@PAVFEModel@@@Z)
    1>dllmain.obj : error LNK2001: unresolved external symbol "public: virtual class FEParam * __thiscall FEMaterial::GetParameter(class ParamString const &)" (?GetParameter@FEMaterial@@UAEPAVFEParam@@ABVParamString@@@Z)
    1>dllmain.obj : error LNK2001: unresolved external symbol "public: virtual void __thiscall FEMaterial::Serialize(class DumpFile &)" (?Serialize@FEMaterial@@UAEXAAVDumpFile@@@Z)
1>dllmain.obj : error LNK2001: unresolved external symbol "public: virtual bool __thiscall FEElasticMaterial::SetAttribute(char const *,char const *)" (?SetAttribute@FEElasticMaterial@@UAE_NPBD0@Z)

    1>dllmain.obj : error LNK2001: unresolved external symbol "public: virtual bool __thiscall FEElasticMaterial::SetAttribute(char const *,char const *)" (?SetAttribute@FEElasticMaterial@@UAE_NPBD0@Z)
    1>dllmain.obj : error LNK2001: unresolved external symbol "public: virtual int __thiscall FEMaterial::Properties(void)" (?Properties@FEMaterial@@UAEHXZ)
    1>dllmain.obj : error LNK2001: unresolved external symbol "public: virtual class FECoreBase * __thiscall FEMaterial::GetProperty(int)" (?GetProperty@FEMaterial@@UAEPAVFECoreBase@@H@Z)
    1>dllmain.obj : error LNK2001: unresolved external symbol "public: virtual int __thiscall FEMaterial::FindPropertyIndex(char const *)" (?FindPropertyIndex@FEMaterial@@UAEHPBD@Z)
    1>dllmain.obj : error LNK2001: unresolved external symbol "public: virtual bool __thiscall FEMaterial::SetProperty(int,class FECoreBase *)" (?SetProperty@FEMaterial@@UAE_NHPAVFECoreBase@@@Z)
    1>dllmain.obj : error LNK2001: unresolved external symbol "public: virtual double __thiscall FESolidMaterial::Density(void)" (?Density@FESolidMaterial@@UAENXZ)
    1>dllmain.obj : error LNK2001: unresolved external symbol "public: virtual void __thiscall FEElasticMaterial::SetLocalCoordinateSystem(class FEElement &,int,class FEMaterialPoint &)" (?SetLocalCoordinateSystem@FEElasticMaterial@@UAEXAAVFEElement@@HAAVFEMaterialPoint@@@Z)
    1>dllmain.obj : error LNK2001: unresolved external symbol "public: virtual double __thiscall FEElasticMaterial::StrainEnergyDensity(class FEMaterialPoint &)" (?StrainEnergyDensity@FEElasticMaterial@@UAENAAVFEMaterialPoint@@@Z)
    1>dllmain.obj : error LNK2019: unresolved external symbol "public: __thiscall FEElasticMaterialPoint::FEElasticMaterialPoint(void)" (??0FEElasticMaterialPoint@@QAE@XZ) referenced in function "public: virtual class FEMaterialPoint * __thiscall FEElasticMaterial::CreateMaterialPointData(void)" (?CreateMaterialPointData@FEElasticMaterial@@UAEPAVFEMaterialPoint@@XZ)
    1>dllmain.obj : error LNK2019: unresolved external symbol "public: virtual __thiscall FEElasticMaterial::~FEElasticMaterial(void)" (??1FEElasticMaterial@@UAE@XZ) referenced in function "public: virtual __thiscall FENeoHookeanPI::~FENeoHookeanPI(void)" (??1FENeoHookeanPI@@UAE@XZ)
    1>FENeoHookeanPI.obj : error LNK2019: unresolved external symbol "protected: void __thiscall FEParamContainer::AddParameter(void *,enum FEParamType,int,class RANGE,char const *)" (?AddParameter@FEParamContainer@@IAEXPAXW4FEParamType@@HVRANGE@@PBD@Z) referenced in function "protected: virtual void __thiscall FENeoHookeanPI::BuildParamList(void)" (?BuildParamList@FENeoHookeanPI@@MAEXXZ)
    1>FENeoHookeanPI.obj : error LNK2019: unresolved external symbol "protected: virtual void __thiscall FESolidMaterial::BuildParamList(void)" (?BuildParamList@FESolidMaterial@@MAEXXZ) referenced in function "protected: virtual void __thiscall FENeoHookeanPI::BuildParamList(void)" (?BuildParamList@FENeoHookeanPI@@MAEXXZ)
    1>FENeoHookeanPI.obj : error LNK2019: unresolved external symbol "public: virtual void __thiscall FEElasticMaterial::Init(void)" (?Init@FEElasticMaterial@@UAEXXZ) referenced in function "public: virtual void __thiscall FENeoHookeanPI::Init(void)" (?Init@FENeoHookeanPI@@UAEXXZ)
    1>FENeoHookeanPI.obj : error LNK2019: unresolved external symbol "public: class mat3ds __thiscall FEElasticMaterialPoint::LeftCauchyGreen(void)" (?LeftCauchyGreen@FEElasticMaterialPoint@@QAE?AVmat3ds@@XZ) referenced in function "public: virtual class mat3ds __thiscall FENeoHookeanPI::Stress(class FEMaterialPoint &)" (?Stress@FENeoHookeanPI@@UAE?AVmat3ds@@AAVFEMaterialPoint@@@Z)
    1>C:\Users\pars\Desktop\example\FEneohookean\Debug\FEneohookean.dll : fatal error LNK1120: 21 unresolved externals
    1>
    1>Build FAILE
Hi every body

I want to make a plugin for a software. In order to make the plugin, I should make a  dll file (a file with dll extension) but I  have faced many challenges about making it . my system is windows 7 and I'm using Microsoft visual studio 2010 as an IDE. I made a dll project and made two source files, and one header file and then I build the solution but I encountered previous errors, (before building the solution I added the path of include and lib directories of the software).  I would appreciate if someone could help me with this problem. 
Thanks'
Faezeh

