C++
is a productivity enhancement tool. Why else would you make the effort (and it
is an effort, regardless of how easy we attempt to make the transition)
to
switch from some language that you already know and are productive in (C, in
this case) to a new language where you’re going to be
less
productive for a while, until you get the hang of it? It’s because
you’ve become convinced that you’re going to get big gains by using
this new tool.
Productivity,
in computer programming terms, means that fewer people can make much more
complex and impressive programs in less time. There are certainly other issues
when it comes to choosing a language, like efficiency (does the nature of the
language cause code bloat?), safety (does the language help you ensure that
your program will always do what you plan, and handle errors gracefully?), and
maintenance (does the language help you create code that is easy to understand,
modify and extend?). These are certainly important factors that will be
examined in this book.
But
raw productivity means a program that might take three of you a week takes one
of you a day or two. This touches several levels of economics. You’re
happy because you get the rush of power that comes from building something,
your client (or boss) is happy because products are produced faster and with
fewer people, and the customers are happy because they get products more
cheaply. The only way to get massive increases in productivity is to leverage
off other people’s code, that is, to use libraries.
A
library
is simply a bunch of code that someone else has written, packaged together
somehow. Often, the most minimal package is a file with an extension like .LIB
and one or more header files to declare what’s in the library to your
compiler. The linker knows how to search through the LIB file and extract the
appropriate compiled code. But that’s only one way to deliver a library.
On platforms that span many architectures, like Unix, often the only sensible
way to deliver a library is with source code, so it can be recompiled on the
new target. And on Microsoft Windows, the
dynamic-link
library
(DLL)
is a much more sensible approach – for one thing, you can often update
your program by sending out a new DLL, which
your
library vendor may have sent you.
So
libraries are probably the most important way to improve productivity, and one
of the primary design goals of C++ is to make library use easier. This implies
that there’s something hard about using libraries in C. Understanding
this factor will give you a first insight into the design of C++, and thus
insight into how to use it.