C++ - Using a .cpp file in another?

Question

just a simple question: Is it possible to use a .cpp file in another .cpp file - Like calling for it.

E.g. File1.cpp:

#include < iostream > 
#include < string >
  using namespace std;

void method(string s);

int main()
{
  method("Hello World");
  return 0;
}

void method(string s)
{
  //get this contents from file2.cpp
}

and File2.cpp:

#include <iostream>

using namespace std;

void method(string s)
{
   cout << s << endl;
}

So to be able to do something along the lines of that. So I dont stuff all my code into 1 cpp file

Thanks.

Yes, you have to link them. Normally, you'd include a header that declares method instead of doing it yourself. — Qaz
– Qaz, Commented Apr 15, 2014 at 14:40
This is about the real basics: .h and .cpp files and linking. I think you should pick up a book or read a beginners tutorial. To answer the question, you can #include 'file2.cpp', but this is not standard practice. — Bgie
– Bgie, Commented Apr 15, 2014 at 14:43
TYpically, you'd want either to not implement method(string s) in file1.cpp for this to work. Or have a different name for method - as the compiler can't tell the two functions apart as it stands. — Mats Petersson
– Mats Petersson, Commented Apr 15, 2014 at 14:44

Chris Maes · Accepted Answer · 2014-04-15 14:44:51Z

2

you need to make a header file; eg File2.h, in which you put the prototype for each of the functions you want to reuse:

#ifndef FILE2_H_
#define FILE2_H_    

void method(string s);

#endif  /* FILE2_H_ */

then you need to include this header both in File2.cpp and File1.cpp:

#include "File2.h"

now in File1.cpp you can just call this function without declaring it:

int main()
{
  method("Hello World");
  return 0;
}

answered Apr 15, 2014 at 14:44

Chris Maes

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Comments

djhaskin987 · Accepted Answer · 2014-04-15 15:12:18Z

0

I'd do it like this: File2.h:

#ifndef __File2_H__
#define __File2_H__

// Define File2's functions...
void method(string s);

#endif

File2.cpp:

#include "File2.h"
// implement them....
void method(string s)
{
    cout << s << endl;
}

File1.cpp

// This include line makes File1.cpp aware of File2's functions
#include "File2.h" 
// and now you can use File2's methods inside method() below.
void method()
{
    method(string("I am batman"));
}

Then link them as @chris said (the following is shell script/commands):

# Compile them first
cc -o file1.o File1.cpp
cc -o file2.o File2.cpp
# Then link them
cc -o program file1.o file2.o

edited Apr 15, 2014 at 15:12

answered Apr 15, 2014 at 14:43

djhaskin987

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3 Comments

Neil Kirk Over a year ago

No discussion of header file?

Chris Maes Over a year ago

indeed, this might work, but it is quite dirty in my opinion... header files are the way to go...

djhaskin987 Over a year ago

Granted, header files are smarter. I'll edit the answer.

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