Question

I’m currently trying to compile an existing project which is a mix of cpp and c.

My makefile is as follows;

execute: mgnsvd.o multifit.o cit.o  main.o
    g++ -Wall -g multifit.o cit.o main.o mgnsvd.o -lgsl -lgslcblas -o execute 

main.o: main.cpp cit.cpp
    g++ -Wall -g -c main.cpp

cit.o: cit.cpp mgnsvd.c multifit.h
   g++ -Wall -g -c cit.cpp

multifit.o: multifit.c mgnsvd.c multifit.h
   g++ -Wall -g -c multifit.c

mgnsvd.o: mgnsvd.c
    g++ -Wall -g -c mgnsvd.c

And my main is a rather plain

// global libraries
#include <iostream>

// local files
#include "cit.cpp"

// using directives
using std::endl;
using std::cout;

// main
int main(){

  cout << "Hello, world" << endl; 

 return 0;
}

If is comment out #include “cit.cpp” it compiles fine. However, if i include it the following error happens;

ld: duplicate symbol _first_function_in_cit in main.o and cit.o for architecture x86_64

_first_function is always the first function, and is not defined or even declared/used anywhere else. A grep of the object files confirms the function seems to be incorporated into main.o, but why? I’ve not worked on a C++/C project before, so maybe I’m making some canonical error? I’m also in OSX, if that makes a difference.

For the record, there are no classes – the .h file contains a few structs and some macros.

Answer 1

cit.cpp is being compiled by itself, and is also included in main.cpp so you’re getting two copies of all the code in it.