How to properly include Header and Implementation Files?

Question

I am a novice programmer in c++, and I am currently getting a compiling error

Undefined symbols for architecture x86_64

Supposedly this originates from how the header files and implementation files are included/coded.

Below is some code that generates the compiling error I am receiving

Main

//Main.cpp
#include <iostream>
#include <string>
#include "Animal.hpp"

using namespace std;

int main(){
    Animal myPet;
    myPet.shout();

    return 0;
}

Header

//Animal.hpp
#ifndef H_Animal
#define H_Animal

using namespace std;

#include <string>

class Animal{
public:
    Animal();

    void shout();
private:
    string roar;
};
#endif

Implementation

//Animal.cpp
#include "Animal.hpp"
#include <string>

Animal::Animal(){
    roar = "...";
}

void Animal::shout(){
    roar = "ROAR";
    cout << roar;
}

This code generates my compiling issue. How would this issue be resolved?

Thanks for your time

EDIT

Undefined symbols for architecture x86_64:
  "Animal::shout()", referenced from:
      _main in test-5f7f84.o
  "Animal::Animal()", referenced from:
      _main in test-5f7f84.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

Can you be more specific about what error message your compiler is giving you? — Logicrat, Aug 07 '15 at 21:03
possible duplicate of [What is an undefined reference/unresolved external symbol error and how do I fix it?](http://stackoverflow.com/questions/12573816/what-is-an-undefined-reference-unresolved-external-symbol-error-and-how-do-i-fix) — Captain Obvlious, Aug 07 '15 at 21:08
Simply including the header files it not enough, you need to compile each .cpp into an object file then link _all_ of those object files together. Given what you've posted it looks like you're only compiling and linking main.cpp. — Captain Obvlious, Aug 07 '15 at 21:10
http://stackoverflow.com/questions/15441877/how-do-i-link-object-files-in-c-problems-with-compilation — 001, Aug 07 '15 at 21:10
@Nicholas Hayden Okay if you have three files, test.cpp(which has main), animal.cpp, and animal.hpp. The command should be `g++ animal.cpp test.cpp`. You need to compile all source files. — James Moore, Aug 07 '15 at 21:22

score 2 · Accepted Answer · answered Aug 07 '15 at 22:53

maybe you might want to see an alternative set of your 3 files, where things are a little more "sorted", you know, where things are put at places where they "really" belong to.

So here's the "new" header file ..

//Animal.hpp
#ifndef H_Animal
#define H_Animal

#include <string> // suffices

// Interface.
class Animal {
    std::string roar; // private

public:
    Animal();
    void shout();
};

#endif

then the source file ..

//Animal.cpp
#include "Animal.hpp"

#include <iostream> // suffices

// Constructor.
Animal::Animal()
    :
    roar("...") // data member initializer
{}

// Member function.
void Animal::shout() {
    roar = "ROAR";
    std::cout << roar;
}

and the main program ..

//Main.cpp
#include "Animal.hpp"

int main(){
    Animal thePet;
    thePet.shout(); // outputs: `ROAR'
}

plus a little GNU makefile ..

all: default run

default: Animal.cpp Main.cpp
    g++ -o Main.exe Animal.cpp Main.cpp

run:
    ./Main.exe

clean:
    $(RM) *.o *.exe

Kick-off things typing just "make" in your cmd-line. Did you like it? -- Regards, M.

5gon12eder · Answer 2 · 2015-08-07T21:18:20.800

I can only find one error in your code and your compiler should have told you that one.

In Animal.cpp, you are using std::cout but you're not #includeing <iostream>. You #include it in Main.cpp but it is not needed there.

If you (really) want to refer to std::cout as cout in Animal.cpp, you also have to add a using namespace std directive in that file.

The using directive in the header file (Animal.hpp) is evil. Get rid of it and type std::string instead. Putting using directives into headers litters the namespaces of all files that use it.

I also don't understand your intentions with the roar member. What is the point of assigning "..." to it in the constructor and re-assigning "ROAR" to it every time shout is called? Couldn't you do without that variable and simply have

void
Animal::shout()
{
  std::cout << "ROAR\n";
}

? I have added a newline because you'd probably want one.

A preferred syntax is `using std::cout;` rather than including the entire namespace. — Thomas Matthews, Aug 07 '15 at 21:32

score 1 · Answer 3 · answered Aug 07 '15 at 22:06

The main issue I was having with this coding project was solved by @JamesMoore.

"@Nicholas Hayden Okay if you have three files, test.cpp(which has main), animal.cpp, and animal.hpp. The command should be g++ animal.cpp test.cpp. You need to compile all source files."

I am currently not using an IDE. So, when I was calling the compiler to compile my main.cpp - It was an issue of compiling the implementation file.

g++ test.cpp

needed to become

g++ test.cpp animal.cpp

This would call the compiler to compile everything the program needed.

How to properly include Header and Implementation Files?

3 Answers3