gcc - How do I link object files in C? Fails with "Undefined symbols for architecture x86_64"

Question

So I'm trying trying to use a function defined in another C (file1.c) file in my file (file2.c). I'm including the header of file1 (file1.h) in order to do this.

However, I keep getting the following error whenever I try to compile my file using gcc:

Undefined symbols for architecture x86_64:
  "_init_filenames", referenced from:
      _run_worker in cc8hoqCM.o
  "_read_list", referenced from:
      _run_worker in cc8hoqCM.o
ld: symbol(s) not found for architecture x86_64

I've been told I need to "link the object files together" in order to use the functions from file1 in file2, but I have no clue what that means :(

Answer 1

I assume you are using gcc, to simply link object files do:

$ gcc -o output file1.o file2.o

To get the object-files simply compile using

$ gcc -c file1.c

this yields file1.o and so on.

If you want to link your files to an executable do

$ gcc -o output file1.c file2.c