Table of Contents for

21st Century C

C has only a handful of keywords and is a bit rough around the edges, and it rocks. You can do anything with it. Like the C, G, and D chords on a guitar, you can learn the basic mechanics quickly, and then spend the rest of your life getting better. The people who don’t get it fear its power and think it too edgy to be safe. By all rankings, it is consistently the most popular language that doesn’t have a corporation or foundation spending money to promote it.^[1]

Also, the language is about 40 years old, which makes it middle-aged. It was written by a few guys basically working against management—the perfect punk rock origins—but that was in the 1970s, and there’s been a lot of time for the language to go mainstream.

What did people do when punk rock went mainstream? In the decades since its advent in the 1970s, punk certainly has come in from the fringes: The Clash, The Offspring, Green Day, and The Strokes sold millions of albums worldwide (to name just a few), and I have heard lite instrumental versions of songs from the punk spinoff known as grunge at my local supermarket. The former lead singer of Sleater-Kinney now has a popular sketch comedy show that frequently lampoons punk rockers.^[2] One reaction to the continuing evolution would be to take the hard line and say that the original stuff was punk and everything else is just easy punk pop for the masses. The traditionalists can still play their albums from the ’70s, and if the grooves are worn out, they can download a digitally mastered edition. They can buy Ramones hoodies for their toddlers.

Outsiders don’t get it. Some of them hear the word punk and picture something out of the 1970s—a historic artifact about some kids that were, at the time, really doing something different. The traditionalist punks who still love and play their 1973 Iggy Pop LPs are having their fun, but they bolster the impression that punk is ossified and no longer relevant.

Getting back to the world of C, we have both the traditionalists, waving the banner of ANSI ’89, and those who will rock out to whatever works and may not even realize that the code they are writing would not have compiled or run in the 1990s. Outsiders don’t get the difference. They see still-in-print books from the 1980s and still-online tutorials from the 1990s, they hear from the hardcore traditionalists who insist on still writing like that today, and they don’t even know that the language and the rest of its users continue to evolve. That’s a shame, because they’re missing out on some great stuff.

This is a book about breaking tradition and keeping C punk rock. I don’t care to compare the code in this book to the original C specification in Kernighan & Ritchie’s 1978 book. My telephone has 512 megabytes of memory, so why are our C textbooks still spending pages upon pages covering techniques to shave kilobytes off of our executables? I am writing this on a bottom-of-the-line red netbook that can accommodate 3,200,000,000 instructions per second; what do I care about whether an operation requires comparing 8 bits or 16? We should be writing code that we can write quickly and that is readable by our fellow humans. We’re still writing in C, so our readable but imperfectly optimized code will still run an order of magnitude faster than if we’d written comparable code in any number of alternative, bloated languages.

Q: How is this C book different from all others?

A: C textbooks are a somewhat uniform bunch (I’ve read a lot of them, including [Griffiths 2012], [Kernighan 1978], [Kernighan 1988], [Kochan 2004], [Oualline 1997], [Perry 1994], [Prata 2004], and [Ullman 2004]). Most were written before the C99 standard simplified many aspects of usage, and you can tell that some of those now in their Nth edition just pasted in a few notes about updates rather than seriously rethinking how to use the language. They all mention that there might be libraries that you could maybe use in writing your own code, but they predate the installation tools and ecosystem we have now that make using those libraries reliable and reasonably portable. Those textbooks are still valid and still have value, but modern C code just doesn’t look like the code in those textbooks.

This book picks up where they left off, reconsidering the language and the ecosystem in which it lives. The storyline here is about using libraries that provide linked lists and XML parsers, not writing new ones from scratch. It is about writing code that is readable and function interfaces that are user-friendly.

Q: Who is this book for? Do I need to be a coding guru?

A: You have experience coding in any language, maybe Java or a scripting language such as Perl. I don’t have to sell you on why your code shouldn’t be one long routine with no subfunctions.

You have some knowledge of C, but don’t worry if you don’t know it too well—as I’ll detail, there’s a lot you’re better off never learning. If you are a blank slate with respect to C syntax, it really is an aggressively simple language, and your search engine will point you to dozens of C tutorials online; if you have experience with another language, you should be able to get the basics in an hour or two.

I might as well point out to you that I have also written a textbook on statistical and scientific computing, Modeling with Data [Klemens 2008]. Along with lots of details of dealing with numeric data and using statistical models for describing data, it has a standalone tutorial on C, which I naturally think overcomes many of the failings of older C tutorials.

Q: I’m an application programmer, not a kernel hacker. Why should I use C instead of a quick-to-write scripting language like Python?

A: If you are an application programmer, this book is for you. I read people asserting that C is a systems language, which impresses me as so un-punk—who are they to tell us what we’re allowed to write?

Statements in the way of “Our language is almost as fast as C, but is easier to write” are so common that they are almost cliché. Well, C is definitely as fast as C, and the purpose of this book is to show you that C is easier to write than the textbooks from decades past imply that it is. You don’t have to call malloc and get elbow-deep in memory management half as often as the systems programmers of the 1990s did, we have facilities for easier string handling, and even the core syntax has evolved to make for more legible code.

I started writing C in earnest because I had to speed up a simulation in a scripting language, R. Like so many other scripting languages, R has a C interface and encourages the user to make use of it any time the host language is too slow. Eventually, I had so many functions jumping out from the R script to C code that I just dropped the host language entirely. Next thing you know, I’m writing a book on modern C technique.

Q: It’s nice that application programmers coming from scripting languages will like this book, but I am a kernel hacker. I taught myself C in fifth grade and sometimes have dreams that correctly compile. What new material can there be for me?

A: C has evolved in the last 20 years. As I’ll discuss later, the set of things we are guaranteed that all C compilers support has changed with time, thanks to two new C standards since the ANSI standard that defined the language for so long. Maybe have a look at Chapter 10 and see if anything there surprises you.

Also, the environment has advanced. Autotools has entirely changed how distribution of code happens, meaning that it is much easier to reliably call other libraries, meaning that our code should spend less time reinventing common structures and routines and more time calling the sort of libraries discussed throughout this book.

Q: I can’t help but notice that about a third of this book has almost no C code in it.

A: Yes, good C practice requires gathering good C tools. If you’re not using a debugger (standalone or part of your IDE), you’re making your life much more difficult. If you tell me that it’s impossible to track down memory leaks, then that means that you haven’t heard of Valgrind, a system designed to point out the exact line where memory leaks and errors occurred. Python and company have built-in package managers; C’s cross-platform package managers are standalone systems that are their own story.

If you use an attractive Integrated Development Environment (IDE) as a wrapper for all these various tools, you may still benefit from knowing how your IDE is dealing with environment variables and other minutiæ that have been hidden from you but still crop up and throw errors at you.

Q: Some of these tools you talk about are old. Aren’t there more modern alternatives to these shell-oriented tools?

A: If we make fun of people who reject new things just because they’re new, then we have no right to reject old things just because they’re old.

One can find reasonable sources putting the first six-string guitar around 1200, the first four-string violin circa 1550, and the piano with keyboard around 1700. The odds are good that most (if not all) of the music you listen to today will involve one of these instruments. Punk rock didn’t happen by rejecting the guitar, but by using it creatively, such as piping the guitar’s output through new filters.

Q: I have the Internet, and can look up commands and syntax details in a second or two, so, really, why should I read this book?

A: It’s true: you can get an operator precedence table from a Linux or Mac command prompt with man operator, so why am I going to put one here?

I’ve got the same Internet you’ve got, and I’ve spent a lot of time reading it. So I have a good idea of what isn’t being talked about, and that’s what I stick to here. When introducing a new tool, like gprof or GDB, I give you what you need to know to get your bearings and ask your search engine coherent questions, and what other textbooks missed (which is a lot).

Unless explicitly stated otherwise, everything in this book conforms to the ISO C99 and C11 standards. To make sense of what that means, and give you some historical background, let us go through the list of major C standards (passing on the minor revisions and corrections).

A decade passed. C went mainstream, in the sense that the base code for more or less every PC and every Internet server was written in C, which is as mainstream as a human endeavor could possibly become.

During this period, C++ split off and hit it big (although not quite as big). C++ was the best thing to ever happen to C. While every other language was bolting on extra syntax to follow the object-oriented trend and whatever other new tricks came to the authors’ minds, C stuck to the standard. The people who wanted stability and portability used C, the people who wanted more and more features so they could wallow in them like moist hundred dollar bills got C++, and everybody was happy.