separate files for classes

Question

I am trying to write code with separate files for classes right now i have 3 files:
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Birthday.h
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#ifndef BIRTHDAY_H
#define BIRTHDAY_H

class Birthday
{
public:
Birthday(int d, int m, int y);
void printdate();

protected:

private:
int day;
int month;
int year;
};

#endif // BIRTHDAY_H

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Birthday.cpp
-----------------------------------------------------------
#include "Birthday.h"

Birthday::Birthday(int d, int m, int y)
: day(d), month(m), year(y)
{
//ctor
}
void Birthday::printdate()
{
cout<<<<day<<"/"<<month<<"/"<<year<<endl;
}
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main.cpp
-----------------------------------------------------------
#include <iostream>
#include "Birthday.h"
using namespace std;
int main()
{
Birthday bd(7, 2, 1992);
bd.printdate();
}

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when i build i get the error:
C:\Users\nisha\AppData\Local\Temp\ccCJXkgP.o:main.cpp:(.text+0x26): undefined reference to `Birthday::Birthday(int, int, int)'
C:\Users\nisha\AppData\Local\Temp\ccCJXkgP.o:main.cpp:(.text+0x32): undefined reference to `Birthday::printdate()'
collect2.exe: error: ld returned 1 exit status

please help!

Answer 1

Hi I fixed it, the problem was with the way i was compiling the code.

i was doing this:
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g++ main.cpp -o test.exe
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instead i had to do this:
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g++ -c Birthday.cpp
g++ -c Person.cpp
g++ -c main.cpp
g++ main.o Birthday.o Person.o -o test.exe

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OR! i could create a make file like this

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Makefile
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# Makefile
# Specify what I need in the end. One single executable
outputFile : main.o Birthday.o Person.o
# Read this as divisionExecutable depends on main.o div.o
# But how is it produced??? Hmm...using the below statement
g++ main.o Birthday.o Person.o -o outputFile
# starts with tab, I repeat tab
# But main.o is not there? So specify how it is produced.
main.o : main.cpp Birthday.h Person.h
g++ -c main.cpp
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the use in cmd
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Mingw32-make
test.exe
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