How to modify makefile for openMP inclusion - macos

Question

HI everybody I am a beginner for both openMP and makefile. Here is my problem.
I usually compile simple openMP code via terminale using:
g++-10 -o file.exe -fopenmp file.cxx
Now I want to modify a code, which consists in many file linked together, adding openMP libraries. Indeed I have to change the already existing makefile and I have no idea how to do it. The openMP libraries are used only in the file "esercizio1.1.cxx".
Here the makefile:
esercizio1.1 : esercizio1.1.o random.o
g++ -o esercizio1.1 esercizio1.1.o random.o
esercizio1.1.o : esercizio1.1.cxx funzioni.h random.h
g++ -c -o esercizio1.1.o esercizio1.1.cxx
random.o : random.cxx random.h
g++ -c -o random.o random.cxx
clean:
rm esercizio1.1
Here an example of how I tried to modify my makefile. I renamed my file and I added
g++-10 -fopenmp
to all the line at the same time, to all the line one per time. but still does not work. Here an example:
esercizio : esercizio.o random.o
g++-10 -fopenmp esercizio.o random.o -o esercizio
esercizio.o : esercizio.cc funzioni.h random.h
g++-10 -fopenmp esercizio.cc -o esercizio.o
random.o : random.cc random.h
g++ random.cc -o random.o
clean:
rm esercizio
Here is the error:
Undefined symbols for architecture x86_64:
"__ZN6Random6RannyuEv", referenced from:
_main._omp_fn.0 in ccA635Wn.o
"__ZN6Random8SaveSeedEv", referenced from:
_main in ccA635Wn.o
"__ZN6Random9SetRandomEPiii", referenced from:
_main in ccA635Wn.o
"__ZN6RandomC1Ev", referenced from:
_main in ccA635Wn.o
"__ZN6RandomD1Ev", referenced from:
_main in ccA635Wn.o
ld: symbol(s) not found for architecture x86_64
collect2: error: ld returned 1 exit status
make: *** [esercizio.o] Error 1
Does it exist a guide for makefile beginner?
Anyway I would appreciate if someone helped me. Thanks in advance.

Answer 1

"C++ compilers are picky and may come with different ABIs, thus mixing different C++ compilers in the same project isn't advised. You are compiling random.cc with g++, which on macOS is a symlink to Apple's clang++. Use g++-10 instead. Also, g++ -o random.o random.cc produces an executable file, not an object file. Leave it as g++-10 -c -o random.o random.cc."
credits to Hristo Iliev. Thank you.