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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)
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    Can you be more specific about what error message your compiler is giving you? Commented Aug 7, 2015 at 21:03
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    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. Commented Aug 7, 2015 at 21:10
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    stackoverflow.com/questions/15441877/… Commented Aug 7, 2015 at 21:10
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    Show the arguments you are passing to clang Commented Aug 7, 2015 at 21:18
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    @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. Commented Aug 7, 2015 at 21:22

3 Answers 3

Reset to default
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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.

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Comments

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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.

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A preferred syntax is using std::cout; rather than including the entire namespace.
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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.

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