main is in function.cc
sub.cxx contains functions.

g++ -c sub.cxx     // create sub.o
nm sub.o   // check the contents

(g++ -o a.exe function.cc sub.o  // making a.exe for execution w/o using library)

ar r libnew.a sub.o     //making library libnew.a

g++ -o c.exe function.o -L. -lnew   // making executable file c.exe

./c.exe