linker-tools-error-lnk2020.md

description	title	ms.date	f1_keywords	helpviewer_keywords	ms.assetid
Learn more about: Linker Tools Error LNK2020	Linker Tools Error LNK2020	11/04/2016	LNK2020	LNK2020	4dd017d0-5e83-471b-ac8a-538ac1ed6870

Linker Tools Error LNK2020

unresolved token 'token'

Similar to an undefined external error, except that the reference is via metadata. In metadata, all functions and data must be defined.

To resolve:

• Define the missing function or data, or

• Include the object file or library in which the missing function or data is already defined.

Examples

The following sample generates LNK2020.

// LNK2020.cpp
// compile with: /clr /LD
ref struct A {
   A(int x);   // LNK2020
   static int f();   // LNK2020
};

// OK
ref struct B {
   B(int x) {}
   static int f() { return 0; }
};

LNK2020 will also occur if you create a variable of a managed template type, but do not also instantiate the type.

The following sample generates LNK2020.

// LNK2020_b.cpp
// compile with: /clr

template <typename T>
ref struct Base {
   virtual void f1() {};
};

template <typename T>
ref struct Base2 {
   virtual void f1() {};
};

int main() {
   Base<int>^ p;   // LNK2020
   Base2<int>^ p2 = gcnew Base2<int>();   // OK
};