Question

Considering it’s a common issue, what could be the source of this error if one uses this file logic:

• Utils.h: declare bool Dummy();
• Utils.cpp: define bool Dummy() {return true;}
• ClassA.h : an irrelevant class A { bool sheet; public: A(); };

• ClassA.cpp: the irrelevant code:

   #include "Utils.h"
   #include "ClassA.h"
   A::A() { sheet = Dummy(); }
  

  Note: all header files contain the guard #pragma once macro.

The error: something like this

Error   2   error LNK2028: unresolved token (0A00000B) "bool __clrcall Dummy(void)" 

Error   3   error LNK2019: unresolved external symbol "bool __clrcall Dummy(void)" .... in ClassA.obj

Answer 1

bool __clrcall Dummy(void)

You are compiling the ClassA.cpp file with /clr in effect, generating managed code. Your Dummy() function however was compiled without /clr, making the calling convention __cdecl. The linker notices the discrepancy, it can’t find the managed implementation for Dummy.

You must tell the compiler that Utils.cpp was built to native code. Fix ClassA.cpp like this:

#pragma managed(push, off)
#include "Utils.h"
#pragma managed(pop)
#include "ClassA.h"
// etc...