How to compile a C++ program via Terminal Mac

Question

I have a question on how to compile a C++ program in Terminal Mac. My program has a header file and a main file. I know that I can't compile both the header file and the main file. and just to compile the main file. I also know that I need to create a name for storing the compiled file. Here is my compile command that I used g++ -o execute1 main.cpp and I get this:

Undefined symbols for architecture x86_64:
"add(int, int)", referenced from:
  _main in main-f2nZvj.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

How can I fix this? Any help will be greatly appreciated. If it helps, below is my code for the two files:

add.h:

int add(int x, int y);

main.cpp:

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

int main(){
    using namespace std;
    cout << "The sum of 9 and 9 is " << add(9, 9) << endl;
    return 0;
}

Solution

You need an add.cpp file that implements your add() function, then you can compile the whole thing as:

$ g++ -Wall main.cpp add.cpp -o execute1

Comments

[Paul R]

Do you have an add.cpp somewhere ?

[Paul R]

@bamboon: not true - gcc/g++ have symbolic links to their more modern counterparts these days.

[Admin]

possible duplicate of What is an undefined reference/unresolved external symbol error and how do I fix it?

[nhgrif]

If it helps, below is my code for the two files .... and where is add.cpp?

[Stephan Dollberg]

@PaulR Sorry for deleting my comment. I first entered "g++" in a ssh session and thought you were right. Do you have any source for your claim? My g++ is still 4.2. To restate what I said, I claimed that mac osx ships with gcc 4.2 and that one shall use clang.

[Paul R]

@bamboon: you may need to install the CLT package for whatever version of Xcode you are using - with Xcode 5 I get the following for g++ -v: Apple LLVM version 5.0 (clang-500.2.79) (based on LLVM 3.3svn)

[Stephan Dollberg]

@PaulR So it was a misunderstanding, I thought you meant that mac osx ships with e.g.: 4.8. gcc seems to be a symlink to clang which is configured to use gcc 4.2 include dir.