1.error LNK2019:unresolved external symbol_func_2 referenced in function "void_cdecl func_1(void)"(?func_1@@YAXXZ)
2.error LNK1120: unresolved externals
[/quote]

I am not sure why and it has been bothering me for days.
The solution is just exporting some DLL's, very simple!
****** Project 1 **************
SHARETAP32.H

#ifdef DLLEXPORTIMPORT
#define EXPORT_IMPORT _declspec(dllexport)
#else
#define EXPORT_IMPORT _declspec(dllimport)
#endif
extern "C" void EXPORT_IMPORT Func_2( int a );


SHARETAP32.CPP

#define DLLEXPORTIMPORT
#include "sharetap32.h"
void func_2( int a )
{
// Stub for now!
}


****** Project 1 **************

****** Project 2 **************
WINDEF32.H

#ifdef DLLEXPORTIMPORT
#define EXPORT_IMPORT _declspec(dllexport)
#else
#define EXPORT_IMPORT _declspec(dllimport)
#endif
extern "C" void EXPORT_IMPORT Func_1();


WINDEF32.CPP

#define DLLEXPORTIMPORT
#include "windef32.h"

****** Project 2 **************

****** Project 3 **************
WINTAP32.H

struct Person
{
char *name;
int age;
};


WINDEF32.CPP

#include "wintap32.h"
#include "sharetap32\sharetap32.h"
void Func_1()
{
func_2( 3 );
}


****** Project 3 **************
Do you guys know what the issue is? I am pretty sure it is due to the func_2( int a ) but I am not sure.