overiding functions defined in a base class with a child class - c++

Question

I am new to C++ and trying to understand inheritance in this language. I have created a Ship class, defined some constructors, mutators, and a print function that should cout some info about the ship. I have two derived classes, one a Cruise class and another a Cargo Class. The first time I compiled a test of the Cruise class everything worked fine. After implementing the Cargo class I could no longer compile my code. Both classes are very similar and implemented nearly identically. Here is my code, the error I have recieved is underneath.
ship.cpp (defines the ship class)
#include <iostream>
#include <string>
using namespace std;
class Ship {
private:
string _strName, _strYear;
public:
//Constructors
Ship();
Ship(string, string);
//Mutators
void setName(string);
void setYear(string);
string getName();
string getYear();
//Methods
virtual void print();
};
//*************************************
// Cunstructors *
//*************************************
Ship::Ship() {
_strName = "NONE";
_strYear = "NONE";
}
Ship::Ship(string strname, string strYear) {
setName(strname);
setYear(strYear);
}
//*************************************
// MUTATORS *
//*************************************
void Ship::setName(string strName) {
_strName = strName;
}
void Ship::setYear(string strYear) {
_strYear = strYear;
}
string Ship::getName() {
return _strName;
}
string Ship::getYear() {
return _strYear;
}
//*************************************
// METHODS *
//*************************************
virtual void Ship::print() {
cout << _strName << endl
<< _strYear << endl;
}
CuiseShip.cpp (cruise ship class that inherits from Ship)
#include <iostream>
#include <string>
#include "ship.cpp"
using namespace std;
class CruiseShip:public Ship {
private:
int _intMaxPassengers;
public:
//Constructors
CruiseShip();
CruiseShip(string, string, int);
//Mutators
void setMaxPassengers(int);
int getMaxPassengers();
//Methods
void print();
};
//*************************************
// Cunstructors *
//*************************************
CruiseShip::CruiseShip() {
setName("NONE");
setYear("NONE");
setMaxPassengers(0);
}
CruiseShip::CruiseShip(string strname, string strYear, int intMaxPassengers) {
setName(strname);
setYear(strYear);
setMaxPassengers(intMaxPassengers);
}
//*************************************
// MUTATORS *
//*************************************
void CruiseShip::setMaxPassengers(int intMaxPassengers) {
_intMaxPassengers = intMaxPassengers;
}
int CruiseShip::getMaxPassengers() {
return _intMaxPassengers;
}
//*************************************
// METHODS *
//*************************************
void CruiseShip::print() {
string name = getName();
string year = getYear();
string maxPassengers = to_string(getMaxPassengers());
cout << name << endl
<< year << endl
<< maxPassengers << endl;;
}
CargoShip.cpp (inherits from ship)
#include <iostream>
#include <string>
#include "ship.cpp"
using namespace std;
class CargoShip: public Ship {
private:
int _intCapacity;
public:
//Constructors
CargoShip();
CargoShip(string, string, int);
//Mutators
void setCapacity(int);
int getCapacity();
//Methods
void print();
};
//*************************************
// Cunstructors *
//*************************************
CargoShip::CargoShip() {
setName("NONE");
setYear("NONE");
setCapacity(0);
}
CargoShip::CargoShip(string strname, string strYear, int intCapacity) {
setName(strname);
setYear(strYear);
setCapacity(intCapacity);
}
//*************************************
// MUTATORS *
//*************************************
void CargoShip::setCapacity(int intCapacity) {
_intCapacity = intCapacity;
}
int CargoShip::getCapacity() {
return _intCapacity;
}
//*************************************
// METHODS *
//*************************************
void CargoShip::print() {
string name = getName();
string year = getYear();
string capacity = to_string(getCapacity());
cout << name << endl
<< year << endl
<< capacity << endl;;
}
TEST.cpp (main() to impliment and test the code)
#include <iostream>
#include <string>
#include "CruiseShip.cpp"
#include "CargoShip.cpp"
int main() {
CruiseShip cruise("cruise", "1862", 25);
CargoShip cargo("Mellinium Falcon", "a long time ago", 100);
cruise.print();
cargo.print();
return 0;
}
Compile Error
In file included from CargoShip.cpp:3:0,
from Test.cpp:4:
ship.cpp:5:7: error: redefinition of ‘class Ship’
class Ship {
^
In file included from CruiseShip.cpp:3:0,
from Test.cpp:3:
ship.cpp:5:7: error: previous definition of ‘class Ship’
class Ship {
^
In file included from CargoShip.cpp:3:0,
from Test.cpp:4:
ship.cpp:27:1: error: redefinition of ‘Ship::Ship()’
Ship::Ship() {
^
In file included from CruiseShip.cpp:3:0,
from Test.cpp:3:
ship.cpp:27:1: note: ‘Ship::Ship()’ previously defined here
Ship::Ship() {
^
In file included from CargoShip.cpp:3:0,
from Test.cpp:4:
ship.cpp:31:1: error: redefinition of ‘Ship::Ship(std::__cxx11::string, std::__cxx11::string)’
Ship::Ship(string strname, string strYear) {
^
In file included from CruiseShip.cpp:3:0,
from Test.cpp:3:
ship.cpp:31:1: note: ‘Ship::Ship(std::__cxx11::string, std::__cxx11::string)’ previously defined here
Ship::Ship(string strname, string strYear) {
^
In file included from CargoShip.cpp:3:0,
from Test.cpp:4:
ship.cpp:39:6: error: redefinition of ‘void Ship::setName(std::__cxx11::string)’
void Ship::setName(string strName) {
^
In file included from CruiseShip.cpp:3:0,
from Test.cpp:3:
ship.cpp:39:6: note: ‘void Ship::setName(std::__cxx11::string)’ previously defined here
void Ship::setName(string strName) {
^
In file included from CargoShip.cpp:3:0,
from Test.cpp:4:
ship.cpp:43:6: error: redefinition of ‘void Ship::setYear(std::__cxx11::string)’
void Ship::setYear(string strYear) {
^
In file included from CruiseShip.cpp:3:0,
from Test.cpp:3:
ship.cpp:43:6: note: ‘void Ship::setYear(std::__cxx11::string)’ previously defined here
void Ship::setYear(string strYear) {
^
In file included from CargoShip.cpp:3:0,
from Test.cpp:4:
ship.cpp:47:8: error: redefinition of ‘std::__cxx11::string Ship::getName()’
string Ship::getName() {
^
In file included from CruiseShip.cpp:3:0,
from Test.cpp:3:
ship.cpp:47:8: note: ‘std::__cxx11::string Ship::getName()’ previously defined here
string Ship::getName() {
^
In file included from CargoShip.cpp:3:0,
from Test.cpp:4:
ship.cpp:51:8: error: redefinition of ‘std::__cxx11::string Ship::getYear()’
string Ship::getYear() {
^
In file included from CruiseShip.cpp:3:0,
from Test.cpp:3:
ship.cpp:51:8: note: ‘std::__cxx11::string Ship::getYear()’ previously defined here
string Ship::getYear() {
^
In file included from CargoShip.cpp:3:0,
from Test.cpp:4:
ship.cpp:58:6: error: redefinition of ‘void Ship::print()’
void Ship::print() {
^
In file included from CruiseShip.cpp:3:0,
from Test.cpp:3:
ship.cpp:58:6: note: ‘void Ship::print()’ previously defined here
void Ship::print() {
^
This error makes little since to me and I can't seem to find a solution. The compiler seems to be telling my that I am trying to redifine the Ship class. Can someone explain what is going on?

Answer 1

You shouldn't ever include .cpp files from you're main file. imagine that #including .cpp files are a copy and paste, and you're including the .cpp files in the main, and in the ship files - which results in multiple copies of these copies, and thus the compiler things you have defined it more than once.
You must place the class definition in the .h files - WITH HEADER GUARDS to protect from this duplication, then the implementation details in the .cpp file. Example:
ship.hpp
// Protects from multiple copies
#ifndef _SHIP_H_
#define _SHIP_H_
#include <iostream>
#include <string>
using namespace std;
class Ship {
private:
string _strName, _strYear;
public:
//Constructors
Ship();
Ship(string, string);
//Mutators
void setName(string);
void setYear(string);
string getName();
string getYear();
//Methods
virtual void print();
};
#endif // _SHIP_H_
ship.cpp
#include "ship.hpp" // this .cpp file INCLUDES the .hpp so it can match the functions
//*************************************
// Constructors *
//*************************************
Ship::Ship() {
_strName = "NONE";
_strYear = "NONE";
}
Ship::Ship(string strname, string strYear) {
setName(strname);
setYear(strYear);
}
//*************************************
// MUTATORS *
//*************************************
void Ship::setName(string strName) {
_strName = strName;
}
void Ship::setYear(string strYear) {
_strYear = strYear;
}
string Ship::getName() {
return _strName;
}
string Ship::getYear() {
return _strYear;
}
//*************************************
// METHODS *
//*************************************
virtual void Ship::print() {
cout << _strName << endl
<< _strYear << endl;
}
repeat the same for the other files.
main.cpp
#include <iostream>
#include <string>
#include "CruiseShip.hpp" // include .hpp files. Linker will link the .hpp functions with the .cpp implementations.
#include "CargoShip.hpp" // same here
int main() {
CruiseShip cruise("cruise", "1862", 25);
CargoShip cargo("Mellinium Falcon", "a long time ago", 100);
cruise.print();
cargo.print();
return 0;
}
To build, you must compile all of the .cpp files separately to ensure they do not have name clashes. They will be linked with the main.cpp automatically:
g++ --std=c++0x ship.cpp cargo.cpp main.cpp ... etc etc etc