I'm trying to compile a little project in C with the following structure: Project | |->Headers |->library.h | |->src |->main.c |->library.c I've checked all my files, my configurations files and I'm getting the same error everytime, someone could please help me? :( Undefined symbols for architecture arm64: "_getfavoritenumber", referenced from: _main in main-99c109.o ld: symbol(s) not found for architecture arm64 clang: error: linker command failed with exit code 1 (use -v to see invocation)