Undefined reference to when including file from separate directory - qt

Question

I have very basic QT application (just create to explain my problem).
So here I go :) I have two folders, f1 and f2, and they are on same level (have same folder for parent). In f1 I have source code from my project, and in f2 another project.
For sake of this example, let's say that in f1 I have only common.h and common.cpp, and in f2 I have:
Test.pro
SOURCES = main.cpp
INCLUDEPATH += "..//f1//"
main.cpp
#include <common.h>
#include <QDebug>
int main(int argc, char *argv[])
{
qDebug()<<CalculateMD5("test");
}
When I try to build this project (Test.pro) I get following error:
f2/main.cpp:7: undefined reference to `CalculateMD5(QString)'
What am I doing wrong ? How should I include code from another project ?
I need CalculateMD5 function to be global.
Here you can download whole example (1kb):
http://www.xx77abs.com/test.rar
Thanks !!

Answer 1

For the simplest change, I think you need to change your .pro file to this:
Test.pro
SOURCES = main.cpp ../f1/common.cpp
INCLUDEPATH += "..//f1//"
If you have other code that will also be linking in common.cpp, then a better change would be to make a .pro file in f1 that generates a library, to be linked in to other applications.
But just manually adding common.cpp to your list of sources should do the trick.