C++: Undefined Reference to 'CYourClass::Method()'

Question

I am struggling to identify the issue with my code in my class inheritance. I've searched many places but can't quite seem to find the right answer. I've made some progress to fix many errors before this, but haven't wrapped it all up quite yet.

The main issue I am running into is undefined references to either methods or constructors in many instances throughout my files. I'm sure I'm probably just missing something stupidly simple somewhere, but being fairly new to C++, it's difficult for me to pinpoint exactly where the issue lies.

Below are the files to my code:

dog.h

#ifndef DOG_H
#define DOG_H

#include <string>

using namespace std;

class Dog{
    public:
        Dog();
        ~Dog(){};
        string dogName = "";
        string Breed = "";
        int age = 0;
        int weight = 0;
        bool subjectToDiscount = false;
        int riskWeight = 0;
        float riskPremium = 0;
        float basePremium = 0;
        virtual float getPremium();
        virtual Dog getDog(char b);
    protected:
        virtual float getBasePremium();
    private:
};

#endif //DOG_H

dog.cpp

#include <iostream>
#include <string>

#include "dog.h"
#include "breeds.h"

using namespace std;

//---default constructor---//
Dog::Dog(){
};

//---methods---//
float Dog::getBasePremium(){
    float val = 0;
    //calculate base premium based on weight
    return val;
};

float Dog::getPremium(){
    float val = 0;
    //calculate actual premium for the dog in question
    if(this->riskWeight == 0){
        val = this->basePremium;
    }else if(this->weight > this-> riskWeight){
        val = this->riskPremium;
    }else val = this->basePremium;

    //add discount if applicable
    if(this->subjectToDiscount && this->age > 13) val *= 0.80;

    //add 25% if over 50kg
    if(this->weight > 50) val *= 1.25;

    return val;
};

Dog Dog::getDog(char b){
    bool recognized = false;
    Dog *pup; 

    while(!recognized){
        switch (b)
        {
        case 'p':
            pup = new Pitbull();
            recognized = true;
            break;
        case 'd':
            pup = new Doberman();
            recognized = true;
            break;
        case 'r':
            pup = new Rottweiler();
            recognized = true;
            break;
        default:
            cout << "Breed code not recognized, please try again...\n";
            break;
        }
    }
    return *pup;
}

int main(){
    return 0;
}

breeds.h

#ifndef BREEDS_H
#define BREEDS_H

#include "dog.h"
#include <string>

using namespace std;

class Pitbull : public Dog{
    public:
        Pitbull();
        ~Pitbull(){};
    protected:
    private:
};

class Doberman : public Dog{
    public:
        Doberman();
        ~Doberman(){};
    protected:
    private:
};

class Rottweiler : public Dog{
    public:
        Rottweiler();
        ~Rottweiler(){};
    protected:
    private:
};

#endif //BREEDS_H

breeds.cpp

#include <iostream>
#include <string>

#include "dog.h"
#include "breeds.h"

using namespace std;

//---constructors---//
Pitbull::Pitbull(){
    this->Breed = "a Pitbull";
    this->basePremium = 30.20f;
    this->riskPremium = 35.15f;
    this->riskWeight = 20;
    this->subjectToDiscount = false;
}

Doberman::Doberman(){
    this->Breed = "a Doberman";
    this->basePremium = 28.16f;
    this->riskPremium = 30.00f;
    this->riskWeight = 35;
    this->subjectToDiscount = true;
}

Rottweiler::Rottweiler(){
    this->Breed = "a Rottweiler";
    this->basePremium = 28.00f;
    this->riskPremium = 29.75f;
    this->riskWeight = 45;
    this->subjectToDiscount = false;
}

int main(){
    return 0;
}

main.cpp

#include <iostream>
#include <iomanip>
#include <string>

#include "dog.h"
#include "breeds.h"

using namespace std;

int getDogCount(){
    int retVal = 0;
    cout << "Please enter the number of dogs in your household: ";
    cin >> retVal;
    return retVal;
}

void run(){
    cout << setiosflags(ios::fixed);
    cout << setprecision(2);

    int dogCount = 0;
    float totalPremium = 0;

    dogCount = getDogCount();

    for(int i = 1; i <= dogCount; i++){
        float premium = 0;
        char breedCode = '.';
        string dogName = "";
        Dog pup;

        cout << "Enter the name of dog #" << i << ": ";
        cin.ignore();
        getline(cin, dogName);

        cout << "Enter the breed code for " << dogName << ": ";
        cin >> breedCode;
        cin.ignore();

        pup = pup.getDog(breedCode);
        pup.dogName = dogName;

        cout << "Enter the current age for " << dogName << ": ";
        cin >> pup.age;
        cin.ignore();

        cout << "Enter the current weight for " << dogName << ": ";
        cin >> pup.weight;

        premium = pup.getPremium();

        cout << "\n";
    }
}

int main(){
    run();

    return 0;
}

These are the errors I get after attempting to compile the 3 .cpp files:

dog.cpp

C:\Users\whitl\AppData\Local\Temp\ccFdz6zr.o: In function `Dog::getDog(char)':
C:\Sandbox\C++\Beginning\Wooffurs/dog.cpp:46: undefined reference to `Pitbull::Pitbull()'
C:\Sandbox\C++\Beginning\Wooffurs/dog.cpp:50: undefined reference to `Doberman::Doberman()'
C:\Sandbox\C++\Beginning\Wooffurs/dog.cpp:54: undefined reference to `Rottweiler::Rottweiler()'
collect2.exe: error: ld returned 1 exit status

breeds.cpp

C:\Users\whitl\AppData\Local\Temp\ccbAKpbb.o: In function `Pitbull::Pitbull()':
C:\Sandbox\C++\Beginning\Wooffurs/breeds.cpp:10: undefined reference to `Dog::Dog()'
C:\Users\whitl\AppData\Local\Temp\ccbAKpbb.o: In function `Doberman::Doberman()':
C:\Sandbox\C++\Beginning\Wooffurs/breeds.cpp:18: undefined reference to `Dog::Dog()'
C:\Users\whitl\AppData\Local\Temp\ccbAKpbb.o: In function `Rottweiler::Rottweiler()':
C:\Sandbox\C++\Beginning\Wooffurs/breeds.cpp:26: undefined reference to `Dog::Dog()'
C:\Users\whitl\AppData\Local\Temp\ccbAKpbb.o:breeds.cpp:(.rdata$_ZTV10Rottweiler[_ZTV10Rottweiler]+0x10): undefined reference to `Dog::getPremium()'
C:\Users\whitl\AppData\Local\Temp\ccbAKpbb.o:breeds.cpp:(.rdata$_ZTV10Rottweiler[_ZTV10Rottweiler]+0x18): undefined reference to `Dog::getDog(char)'
C:\Users\whitl\AppData\Local\Temp\ccbAKpbb.o:breeds.cpp:(.rdata$_ZTV10Rottweiler[_ZTV10Rottweiler]+0x20): undefined reference to `Dog::getBasePremium()'
C:\Users\whitl\AppData\Local\Temp\ccbAKpbb.o:breeds.cpp:(.rdata$_ZTV8Doberman[_ZTV8Doberman]+0x10): undefined reference to `Dog::getPremium()'
C:\Users\whitl\AppData\Local\Temp\ccbAKpbb.o:breeds.cpp:(.rdata$_ZTV8Doberman[_ZTV8Doberman]+0x18): undefined reference to `Dog::getDog(char)'
C:\Users\whitl\AppData\Local\Temp\ccbAKpbb.o:breeds.cpp:(.rdata$_ZTV8Doberman[_ZTV8Doberman]+0x20): undefined reference to `Dog::getBasePremium()'
C:\Users\whitl\AppData\Local\Temp\ccbAKpbb.o:breeds.cpp:(.rdata$_ZTV7Pitbull[_ZTV7Pitbull]+0x10): undefined reference to `Dog::getPremium()'
C:\Users\whitl\AppData\Local\Temp\ccbAKpbb.o:breeds.cpp:(.rdata$_ZTV7Pitbull[_ZTV7Pitbull]+0x18): undefined reference to `Dog::getDog(char)'
C:\Users\whitl\AppData\Local\Temp\ccbAKpbb.o:breeds.cpp:(.rdata$_ZTV7Pitbull[_ZTV7Pitbull]+0x20): undefined reference to `Dog::getBasePremium()'
C:\Users\whitl\AppData\Local\Temp\ccbAKpbb.o:breeds.cpp:(.rdata$.refptr._ZTV3Dog[.refptr._ZTV3Dog]+0x0): undefined reference to `vtable for Dog'
collect2.exe: error: ld returned 1 exit status

main.cpp

C:\Users\whitl\AppData\Local\Temp\ccgKyBTC.o: In function `run()':
C:\Sandbox\C++\Beginning\Wooffurs/main.cpp:30: undefined reference to `Dog::Dog()'
C:\Sandbox\C++\Beginning\Wooffurs/main.cpp:40: undefined reference to `Dog::getDog(char)'
C:\Sandbox\C++\Beginning\Wooffurs/main.cpp:50: undefined reference to `Dog::getPremium()'
C:\Users\whitl\AppData\Local\Temp\ccgKyBTC.o:main.cpp:(.rdata$.refptr._ZTV3Dog[.refptr._ZTV3Dog]+0x0): undefined reference to `vtable for Dog'
collect2.exe: error: ld returned 1 exit status

Thank you to anyone that helps, I really appreciate it. Please give my any pointers on my code as well, and how to possibly better pose questions on Stack Overflow.

Welcome to SO! Please consider providing a [Minimal, Reproducible Example](https://stackoverflow.com/help/minimal-reproducible-example). — rawrex, Jun 30 '21 at 03:36
Those look like a linker errors, your code looks fine. How are you compiling your code? Linker errors are when you don't include all the necessary object files (results of compilation). — marcinj, Jun 30 '21 at 03:36
proper compilation should look like this: g++ main.cpp dog.cpp breads.cpp -o myprogram — marcinj, Jun 30 '21 at 03:40
How are you compiling this? If it's a makefile or command-line, please post it -- you may be missing a link step. — Human-Compiler, Jun 30 '21 at 04:05
Since you are getting "undefined reference" (a linker error) for *each* source file, this looks like it falls under [Failure to link against appropriate object files](https://stackoverflow.com/questions/12573816/what-is-an-undefined-reference-unresolved-external-symbol-error-and-how-do-i-fix/12574400#12574400), as you seem to be linking each translation unit independently. Compile each source file to an object file, then link those object files together. *Hmm... that link does not cover generating the object files. :(* — JaMiT, Jun 30 '21 at 04:26

score 0 · Accepted Answer · answered Jun 30 '21 at 04:18

It looks as though you are doing something like:

g++ dog.cpp -o dog

Without the -c flag (for compile only, don't link) the compiler will attempt to make an executable from that one file.

Generally speaking you need to do one of the following:

Compile each cpp file separately, and then link at the end

# compilation
g++ -c dog.cpp -o dog.o
g++ -c breeds.cpp -o breeds.o
g++ -c main.cpp -o main.o

# now link the 3 object files into the exe
g++ -o myApp main.o dog.o breeds.o

Compile them in one go

g++ -o myApp main.cpp dog.cpp breeds.cpp

Use a makefile

all : myApp

# dog.o depends on dog.cpp & breeds.h. When those change, run line below
dog.o: dog.cpp breeds.h
     gcc -c -o dog.o dog.cpp

breeds.o: breeds.cpp dog.h
     gcc -c -o breeds.o breeds.cpp

main.o: main.cpp breeds.h dog.h
     gcc -c -o main.o dog.cpp

# final app depends on the object files, when they change, recompile.
myApp: main.o dog.o breeds.o
     gcc -o myApp main.o dog.o breeds.o

clean:
    rm -f *.o

Use some IDE to manage this for you (or use something like cmake)

Seems like a reasonable answer, but it's a bit of a shot-in-the-dark unless OP clarifies how they are building the project — Human-Compiler, Jun 30 '21 at 04:20

C++: Undefined Reference to 'CYourClass::Method()'

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