Question

Let’s say that there is this command:

g++ main.o somefile.o -lc -o main

What is the difference between linking object file somefile.o and linking library libc.a?

Answer 1

Files ending in “.a” are archive files. They essentially contain a set of “.o”s. Therefore, assuming “libc.a” contains “c1.o”, “c2.o” and “c3.o”, your command is essentially equivalent to unarchiving “libc.a”, then invoking:

g++ main.o somefile.o c1.o c2.o c3.o -o main

Note that, the objects contained in the “.a” are only included if required, i.e., if at least one of their symbols is referenced by another “.o”.