c++ - Undefined reference error at class instantiation -

this main.cpp. program starts here , have problem:

i 2 errors:

undefined reference `bankcontroller::bankcontroller(transactionrepository)* @ line 23

and

undefined reference `transactionfilerepository::transactionfilerepository(std::string) @ line 19

for both of them, type c/c++ problem, resource main.cpp

#include "bankgui.h" #include "controller/bankcontroller.h" #include "repository/transactionfilerepository.h" #include "repository/transactionmemoryrepository.h" #include "repository/transactionrepository.h"  #include <qtgui> #include <qapplication> #include <string> #include <iostream> using namespace std;  int main(int argc, char *argv[]){    string path = "datastorage/database.txt";    //instantiate main data repository   transactionrepository* maindatabase;   maindatabase = new transactionfilerepository(path); // <-- error here    //instantiate main controller   bankcontroller* maincontroller;   maincontroller = new bankcontroller(maindatabase); // <-- same error here    //starts gui   qapplication app(argc, argv);   bankgui* mainwidget;   mainwidget = new bankgui(maincontroller);   mainwidget->show();    return app.exec(); } 

i have 3 classes:

• a virtual transactionrepository

• one class implements above transactionmemoryrepository

• one class inherits above transactionmemoryrepository transactionfilerepository

i've been searching several hours on google solutions try doesn't rid of errors.

i should mention c++ qt project working on. had add project properties include paths things work.

all files #included exist.

this linker error. means parts (the different .cpp files) of program compiled linker can't figure out how put them together.

just have use #includes (of .h files) tell compiler function defined in different file need give parameters linker use compiled files (those created .cpp) find functions

the compilation process described in answer question.