Section 2. Platform-independent library design
Introduction
You use them all the time, but have you ever thought about what goes into making a
good library? Have you ever thought about how much work the maintainer had to put in
for you to be able to "seamlessly" compile your favorite free software library on your
particular marginal platform -- or your client's platform du jour?
This tutorial discusses design issues and how to avoid some common cross-platform
pitfalls. (We're sure we haven't covered all of them, and very much welcome more tips
from you.) Then we'll go through how to actually build a shared library, using GNU tools
and MSVC.
Recently, we converted spline.exe, a spline generation Unix utility distributed with GNU
plotutils, to be a cross-platform shared library. We'll use examples from this conversion
throughout the tutorial. In the design phase, we encourage you to apply the steps in
this tutorial to some of your own code that you'd like to turn into a library. When we
discuss the mechanics of shared library creation, however, you will probably find it
useful to follow along, both with the original code and with our gspline library, which
you can download as a .zip file or as .tar.gz file .
What's a spline?
Merriam-Webster's defines a spline as: a function that is defined on an interval, is used
to approximate a given function, and is composed of pieces of simple functions defined
on subintervals and joined at their endpoints with a suitable degree of smoothness
For our purposes, we can define a spline as a fancy smooth curve based on three or
more control points and a tension. Splines are used to draw smooth curves through
specific points. The tension parameter controls how sharply the spline is allowed to
curve. For those who care deeply, 0 tension splines are simple cubic splines and
nonzero tension splines obey the equation: y'''' = t^2 * y''.
The Jargon File has yet another take on the definition of spline: [XEROX PARC] This
phrase expands to: "You have just used a term that I've heard for a year and a half,
and I feel I should know, but don't. My curiosity has finally overcome my guilt." The
PARC lexicon adds "Moral: don't hesitate to ask questions, even if they seem obvious."
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Building a cross-platform C library Page 3
