Re: linking 2 projects together - getting 'unresolved external symbol' error

David Wilkinson <>
Wed, 08 Aug 2007 10:08:59 -0400
pwalker wrote:

Hi I am hoping someone can help me.

I have set up a VC++ 2005 solution containing three project folders:
myFunction, myMain1 and myMain2.

myFunction contains a set of functions that I would like to utilise in my
other projects, namely myMain1 and myMain2.

myMain1 and myMain2 simply try and instantiate the object contained in
myFunction, so as to utilise the functions within myFunction. myFunction
builds ok. The problem is that I get an error LNK2019: unresolved external
symbol error when I try and build myMain1 and myMain2.

Here is the reduced content of the above projects:

1) myFunction project contains:


// ttest.h ----begin

#ifndef TTEST_H
#define TTEST_H

class TTEST


  void TTEST :: out( void );


// test.h -----end


// ttest.cpp ----begin

#include <iostream>
#include "ttest.h"


void TTEST::out(void)
 std::cout << "hi";

// ttest.cpp -----end


// ttestmain.cpp ----begin

#include <iostream>
#include "ttest.h"

int main(int argc, char** argv)
 TTEST myt = TTEST();


 int n;
 std::cin >> n;

 return 0;

// testmain.cpp ----end


2) myMain1 project contains:

// realmain.cpp ----begin

#include <iostream>
#include "ttest.h"

int main(int argc, char** argv)
 TTEST myt = TTEST();


 int n;
 std::cin >> n;

 return 0;

// realmain.cpp ----end

Within the myMain project I have gone to properties > C++ > Additional
include Directories, and placed the path to the directory containing

Note that when I build myFunction, it works ok and the function outputs "hi"
to the screen. I want to execute that same function from myMain1's

This does work if I include all the above files within a 'single' project
folder within the VC++ solution. however if i have two separate project
folders as constructted above, it doesnt link and complains of unresolved
external symbol:

myMain1.obj : error LNK2019: unresolved external symbol "public: void
__thiscall TTEST::out(void)" (?out@TTEST@@QAEXXZ) referenced in function
myMain1.obj : error LNK2019: unresolved external symbol "public: __thiscall
TTEST::TTEST(void)" (??0TTEST@@QAE@XZ) referenced in function _main
F:\Tools\Microsoft\Visual Studio Projects\test\MSVC\Debug\test.exe : fatal
error LNK1120: 2 unresolved externals

Can anyone tell me what I need to do to gett he above configuration working?


The easiest thing to do is just add ttest.cpp to the other two projects.
Remember that the items in the Solution Explorer folders are not actual
files, but rather links to files. Use "Add existing item" and navigate
to the actual file ttest.cpp in the myfunction project directory.

David Wilkinson
Visual C++ MVP

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