hi, i am build a program, the structure of the source is below, main.o main.c libfoo.a foo.c libbar.a bar.c and, the foo.c has a reference to function bar() which is defined in bar.c i can successfully compile and produce libfoo.a and libbar.a. but when compile main.o, i get an error like following: gcc -g -O2 -o main.o main.o libfoo.a libbar.a libfoo.a(libfoo_a-foo.o): in function 'foo': foo.c: undefined reference to 'bar' what's the cause and how do i do? thanks. -- woody