Static libraries are simply collections of object files arranged by the ar (archiver) utility. ar collects object files into one archive file and adds a table that tells which object files in the archive define what symbols. The linker, ld, then binds references to a symbol in one object file to the definition of that symbol in an object file in the archive. Static libraries use the suffix .a.

You can convert a group of object files into a static library with a command like

ar rcs libname.a foo.o bar.o baz.o  

You can also add one object file at a time to an existing archive.

ar rcs libname.a foo.o  ar rcs libname.a bar.o  ar rcs libname.a baz.o  

In either case, libname.a will be the same. The options used here are:

There is rarely any need to use other options when building static libraries. However, ar has other options and other capabilities; the ar man page describes them in detail.