separate classes in different cpp files

Question

I'm trying to separate classes to different cpp files.

my files are:

Source.h:

#pragma once

#include "stdafx.h"
#include <iostream>


class printData {
public:

    void print(int i);

    void print(double  f);

    void print(char* c);
};

Source.cpp:

#include "stdafx.h"
#include <iostream>

using namespace std;

class printData {
public:


    void print(int i) {
        cout << "Printing int: " << i << endl;
    }

    void print(double  f) {
        cout << "Printing float: " << f << endl;
    }

    void print(char* c) {
        cout << "Printing character: " << c << endl;
    }
};

ConsoleApplication3.cpp:

#include "stdafx.h"
#include <iostream>
#include "Source.h"

using namespace std;


int main(void) {

    printData pd;

    // Call print to print integer
    pd.print(5);

    // Call print to print float
    pd.print(500.263);

    // Call print to print character
    pd.print("Hello C++");

    return 0;
}

But when i try to build to project i'm getting :

1>ConsoleApplication3.obj : error LNK2019: unresolved external symbol "public: void __thiscall printData::print(int)" (?print@printData@@QAEXH@Z) referenced in function _main
1>ConsoleApplication3.obj : error LNK2019: unresolved external symbol "public: void __thiscall printData::print(double)" (?print@printData@@QAEXN@Z) referenced in function _main
1>ConsoleApplication3.obj : error LNK2019: unresolved external symbol "public: void __thiscall printData::print(char *)" (?print@printData@@QAEXPAD@Z) referenced in function _main

If i will combine all the files to just ConsoleApplication3.cpp there will be no error.

It seems like Source.cpp is not compiled. How do you call the compiler? — wkl
– wkl, Commented May 16, 2017 at 9:57
@Angew Yes, of course. By 'Not compiled', I meant it was missing in the call to the compiler. (Where compiler means the total of preprocessor, actual compiler and linker). However, most probably it is not linked because it has not been compiled before. :-) — wkl
– wkl, Commented May 16, 2017 at 10:05

KjMag · Accepted Answer · 2017-05-16 10:27:24Z

1

You've got two errors here:

You don't include .h file in your corresponding .cpp file.
You have a class redefinition in .cpp file.

In your .cpp file, you should define your methods as follows:

#include "stdafx.h"
#include <iostream>
#include "Source.h"

using namespace std;

void printData::print(int i) {
    cout << "Printing int: " << i << endl;
}

void printData::print(double  f) {
    cout << "Printing float: " << f << endl;
}

void printData::print(char* c) {
    cout << "Printing character: " << c << endl;
}

Don't write this class printData etc. in .cpp file as it is another definition of the class defined in Source.h. You should only define the class methods themselves in the .cpp file in the way shown above.

The compiler complains because all the main.cpp file sees is a Source.h file, which has a class that is only declared, not defined, as Source.cpp doesn't include Source.h. But even if you did include Source.h in Source.cpp, you would get a class redefintion error for the reason given above.

edited May 16, 2017 at 10:27

answered May 16, 2017 at 10:02

KjMag

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4 Comments

j rollin Over a year ago

which .cpp file?

KjMag Over a year ago

Source.cpp has to include Source.h in order to be linked properly. Source.cpp should also have the class methods defined in a way that I have described in the answer.

j rollin Over a year ago

1>c:\users\minche\documents\visual studio 2017\projects\consoleapplication3\consoleapplication3\source.cpp(7): error C2011: 'printData': 'class' type redefinition 1>c:\users\minche\documents\visual studio 2017\projects\consoleapplication3\consoleapplication3\source.h(5): note: see declaration of 'printData'

KjMag Over a year ago

No problem. You may accept this answer if you think that it solves your problem.

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