Question

I am to compile a multi-file C++ program, and have the following error;

Undefined symbols for architecture i386:
  "included::printMSG()", referenced from:
      _main in ccQwMj1l.o
ld: symbol(s) not[Finished in 0.3s with exit code 1] found for architecture i386
collect2: ld returned 1 exit status

My code:
main.cpp: https://gist.github.com/3845822

included.cpp: https://gist.github.com/3845825

included.h: https://gist.github.com/3845827

(confirmed to work with g++)

EDIT: I am not putting these files in a project, they are just all in the same folder, and I’m compiling main.cpp

Answer 1

You can’t just compile a single file and hope all other files are automatically linked to it to create the final program.

One way to make that happen is to use a program called make, which reads a Makefile that has rules that make follows`.

A simple Makefile can look like this:

CXXFLAGS = -Wall -g

my_pogram: main.o other_file.o third_file.o
    g++ main.o other_file.o third_file.o -o my_program

main.o: main.cpp
    g++ $(CXXFLAGS) -c -o main.o main.cpp

other_file.o: other_file.cpp
    g++ $(CXXFLAGS) -c -o other_file.o other_file.cpp

third_file.o: third_file.cpp
    g++ $(CXXFLAGS) -c -o third_file.o third_file.cpp

There are other similar programs to handle this. One that is popular is CMake.