I am having a very unusual problem:
I keep getting multiple definition of functions in my class.
This is my main .cpp
#include <iostream>
#include "Calculation.cpp"
using namespace std;
int main()
{
cout << "Hello world!" << endl;
return 0;
}
this is my class .h
#ifndef CALCULATION_H_INCLUDED
#define CALCULATION_H_INCLUDED
class Calculation
{
public:
Calculation();
private:
};
#endif // CALCULATION_H_INCLUDED
this is my implementation file .cpp
#include "Calculation.h"
Calculation::Calculation()
{
}
Please help me; I have tried to create a new project but that didn't help.
All help is appreciated.
make your main.cpp like :
#include <iostream>
#include "Calculation.h" // not Calculation.cpp
using namespace std;
int main()
{
cout << "Hello world!" << endl;
return 0;
}
You have to include your Calculation.h in th main.cpp and you have to compile it as follows,
g++ main.cpp Calculate.cpp -o main -I<path for your .h file>
main.cpp
#include<iostream>
#include "Calculation.h"
//using namespace std; // Avoid this, always to use std::cout .. etc on place
int main()
{
Calculation c; //Creating the object of Calculation class
std::cout<<"Hello World!"<<std::endl;
return 0;
}
Related
i am using eclipse on mac to run c++ program. I am new to c++ and was trying to learn composition by using different classes individually.I am facing the issue in the following line of the code
Main.cpp
#include <iostream>
using namespace std;
#include "Birthday.h"
#include "People.h"
int main() {
cout << "!!!Hello World!!!" << endl; // prints !!!Hello World!!!
Birthday obj(25,3,1993);
obj.print();
People pp(5,obj);
pp.printinfo();
return 0;
}
Birthday.cpp
#include <iostream>
using namespace std;
#include "Birthday.h"
//#include "People.h"
Birthday::Birthday(int d,int m,int y){
// TODO Auto-generated constructor stub
date =d;
month=m;
year=y;
}
void Birthday::print()
{
cout <<date << month<<year<<endl;
}
People.h
#ifndef PEOPLE_H_
#define PEOPLE_H_
//using namespace std;
#include "Birthday.h"
class People {
public:
People(int x,Birthday bb);
void printinfo();
private:
int xx;
Birthday bo;
};
#endif /* PEOPLE_H_ */
People.cpp
#include "People.h"
#include <iostream>
using namespace std;
#include "Birthday.h"
#include<string>
People::People(int x,Birthday bb)
:xx(x),bo(bb)
{
// TODO Auto-generated constructor stub
}
void People::printinfo()
{
cout<< xx<<bo.print(); //I am getting error because of this line , as soon as i comment it program compiles fine.
}
I have tried to use string variable instead of xx variable but it was giving me some other error.So i tried to simplify and learn the concept of compostion before jumping into strings manipulation directly.
cout << xx << bo.print();
bo.print() - function and they not have return value (void)
Just write:
cout << xx;
bo.print();
I created a new project in c++ but i keep getting the same error
Main.cpp
#include <iostream>
#include <string.h>
#include "Computer.cpp"
#include "Computer.h"
using namespace std;
int main()
{
cout << "Hello World!" << endl;
return 0;
}
Computer.h
#ifndef COMPUTER_H_INCLUDED
#define COMPUTER_H_INCLUDED
#include <string>
class Computer
{
public:
std::string marca;
float prezzo;
bool acceso;
Computer();
void Accenditi();
void Spegniti();
void ImpostaMarca(std::string m);
void ImpostaPrezzo(float p);
};
#endif
Computer.cpp
#include "Computer.h"
Computer::Computer()
{
}
void Computer::Accenditi()
{
if(!acceso)
{
acceso = true;
}
else
{
std::cout << "Sono già acceso";
}
}
void Computer::Spegniti()
{
if(acceso)
{
acceso = false;
}
else
{
std::cout << "Sono già spento";
}
}
void Computer::ImpostaMarca(std::string m)
{
marca = m;
}
void Computer::ImpostaPrezzo(float p)
{
prezzo = p;
}
The Problem
i don't understand what's wrong with Computer.cpp, i keep getting "cout is not a member of std". I tryed to add "using namespace std" and i also tryed to add the library #include but i get a new file called "makefile.win". How can i fix this error ?
You need to include iostream header in your Computer.cpp file as such:
include <iostream>
and to make your life easier, you can also add:
using std::cout;
using std::endl;
right at the bottom of your include, that way you don't have to keep adding "std::cout" everytime, you can just use "cout"
Also want to add:
You can remove the include computer.cpp from your main.cpp and just leave the header. The C++ linker will automatically link your computer.h and computer.cpp together since .cpp includes the header, and your main includes the computer.h
Add # include <iostream> at the files that you use std::cout and std::cin.
**PROBLEM SOLVED. It appears that i had created an extra header by mistake, and since i deleted him , it worked. **
So i am trying to understand about classes and headers and how i can make them work together.
I am following an online tutorial but it seems that something is going wrong in my code.
The problem is that when i try to run the main it gives me this error:
multiple definition of Cat::speak() and all the other functions.
main.cpp
#include <iostream>
#include "class.h"
using namespace std;
int main()
{
Cat jim;
jim.makehappy();
jim.speak();
Cat george;
george.makesad();
george.speak();
return 0;
}
class.cpp
#include <iostream>
#include "class.h"
using namespace std;
void Cat::speak()
{
if (happy)
{
cout << "meoww" << endl;
}
else
{
cout << "sssss" << endl;
}
}
void Cat::makehappy()
{
happy = true;
}
void Cat::makesad()
{
happy = false;
}
class.h
#ifndef CLASS_H_INCLUDED
#define CLASS_H_INCLUDED
class Cat
{
private:
bool happy;
public:
void makehappy();
void makesad();
void speak();
};
#endif // CLASS_H_INCLUDED
From what you have shown here there should be no problems. What you could do to temporarily resolve this to find out if you are actually defining this function in several places is to wrap your class in a namespace.
class.h
#ifndef CLASS_H_INCLUDED
#define CLASS_H_INCLUDED
namespace myNamespace {
class Cat {
private:
bool happy;
public:
void makehappy();
void makesad();
void speak();
};
} // namespace myNamespace
#endif // CLASS_H_INCLUDED
class.pp
#include <iostream>
#include "class.h"
// using namespace std; // Don't Use - This is Bad Practice
// Can cause name clashing when trying to resolve name lookup
namespace myNamespace {
void Cat::speak() {
if (happy) {
std::cout << "meoww" << std::endl;
} else {
std::cout << "sssss" << std::endl;
}
}
void Cat::makehappy() {
happy = true;
}
void Cat::makesad() {
happy = false;
}
} // namespace myNamespace
main.cpp
#include <iostream>
#include "class.h"
// using namespace std; // Again -Bad Practice
int main() {
using namespace myNamespace;
Cat jim;
jim.makehappy();
jim.speak();
Cat george;
george.makesad();
george.speak();
return 0;
}
Try this to see if you are getting the same compiler error. This should help you to see if you are defining this function in multiple spaces. Also by removing the using namespace std; and just using the scope resolution operator to the std:: namespace will help to eliminate any possible problems and any possible future problems.
How are you compiling the code? You need to make sure that you are building the specific "class.o" and "main.o" files separately before linking them together. Here is an example Makefile.
all: main
main: main.o class.o
g++ main.o class.o -o main
main.o: main.cpp class.h
g++ -c main.cpp
class.o: class.cpp class.h
g++ -c class.cpp
It looks like you are using double inclusion guards so I don't think that is the problem. Check out this answer for a more in-depth explanation of what is happening: Error with multiple definitions of function
This question already has answers here:
Resolve build errors due to circular dependency amongst classes
(12 answers)
Closed 7 years ago.
Please see my previous post here:
Undefined type error even with forward declaration
I moved the definitions to cpp files and I still face the issue. Any ideas why? My files look like this:
Header1.hpp
#ifndef HEADER1_HPP
#define HEADER1_HPP
namespace sample_ns
{
class sample_class{
public:
static int getNumber();
static void print();
};
}
#endif
Header2.hpp
#ifndef HEADER2_HPP
#define HEADER2_HPP
namespace sample_ns
{
class sample_class2{
public:
sample_class2();
int getNumber2();
};
}
#endif
Source1.cpp
#include "Header1.hpp"
#include "Header2.hpp"
#include "stdafx.h"
#include <iostream>
namespace sample_ns
{
int sample_class::getNumber()
{
sample_class2 obj;
return obj.getNumber2();
}
void sample_class::print()
{
std::cout << "Print utility function" << std::endl;
}
}
Source2.cpp
#include "Header2.hpp"
#include "Header1.hpp"
#include "stdafx.h"
#include <iostream>
namespace sample_ns
{
sample_class2::sample_class2()
{
sample_class::print();
}
int sample_class2::getNumber2()
{
sample_class::print();
return 5;
}
}
In my main I call it as:
std::cout << sample_ns::sample_class::getNumber() << std::endl;
I get 'sample_class2' : undeclared identifier. I tried adding class sample_class2; but that still gives me error
EDIT:
my main file:
#include "stdafx.h"
#include <iostream>
#include "Header1.hpp"
int _tmain(int argc, _TCHAR* argv[])
{
std::cout << "hello" << std::endl;
std::cout << sample_ns::sample_class::getNumber() << std::endl;
return 0;
}
The best practice for declaring classes and namespaces in header and cpp files is using structure likes below:
Header1.hpp
#ifndef HEADER1_HPP
#define HEADER1_HPP
#include "Header2.hpp"
#include <iostream>
namespace sample_ns
{
class sample_class{
public:
static int getNumber();
static void print();
};
}
#endif
Source1.cpp
#include "Header1.hpp"
namespace sample_ns
{
int sample_class::getNumber()
{
sample_class2 obj;
return obj.getNumber2();
}
void sample_class::print()
{
std::cout << "Print utility function" << std::endl;
}
}
So by including in header files and using ifndef you become sure that circular dependencies will not occure.
How to include file 2 in file 1. What changes I need to make in file 2.
file 1
#include <iostream>
using namespace std;
int main()
{
cout<<"Hello World";
return 0;
}
file 2
int otheFun()
{
cout<<"Demo Program";
return 0;
}
You do not include cpp files in to another cpp files.
Also, a c++ program can have only one main() function.
If you are trying to play around with a program which has multiple files, You will need to have something like this:
file2.cpp
#include <iostream>
#include "file2.h"
int printHelloWorld()
{
std::cout<<"Hello World";
return 0;
}
file2.h
#ifndef FILE2_H <----Lookup Inclusion Guards on google, this is important concept to learn.
#define FILE2_H
int printHelloWorld();
#endif //FILE2_H
file1.cpp
#include <iostream>
#include "file2.h"
int main()
{
std::cout<<"Demo Program";
printHelloWorld();
return 0;
}
What changes I need to make in file 2?
#include <iostream>
using namespace std;
int main()
{
cout << "Hello world";
cout << "Demo Program";
}