c++ - What g++ link option to fix the error function not found -

my project uses g++ compiler compile source code distributed on several directories, executable built. in building final executable link error function not defined.

i cooked following code scaled down of project , exposes same error, hope me out.

so here directory tree , source files:

./  ./11/ c1.cpp  c1.h  ./12/ c2.cpp 

here files:

./11/c1.h: int f();  ./11/c1.cpp: #include "c1.h"  int f() {     return 0; }  ./12/c2.cpp: #include "c1.h"  int main() {     f();      return 0; } 

here steps build files:

cd 11 g++ -c -o ../c1.o c1.cpp cp c1.h .. cd .. ar cr libc1.a c1.o cd 12 g++  -i../ -l../ -lc1 c2.cpp 

yes, need compile c1 object , archive small, how project doing.

and here error message:

/tmp/cctfdzle.o: in function `main': c2.cpp:(.text+0x5): undefined reference `f()' collect2: ld returned 1 exit status 

thanks!