2.4 Compiling files independently
If a program is stored in a single file then any change to an individual
function requires the whole program to be recompiled to produce a new
executable. The recompilation of large source files can be very
When programs are stored in independent source files, only the files
which have changed need to be recompiled after the source code has been
modified. In this approach, the source files are compiled
separately and then linked together--a two stage process. In the
first stage, a file is compiled without creating an executable. The
result is referred to as an object file, and has the extension
'.o' when using GCC.
In the second stage, the object files are merged together by a separate
program called the linker. The linker combines all the
object files to create a single executable.
An object file contains machine code where any references to the memory
addresses of functions (or variables) in other files are left undefined.
This allows source files to be compiled without direct reference to each
other. The linker fills in these missing addresses when it produces the