Upcoming Arrival

I imagine most of my regular readers have already found this out through other channels, but we're expecting. (Really it is Vanessa who is expecting, I have never really figured out why people say "we".) The bouncing baby bundle should be arriving in the very near future, so we've decide to guess the delivery date, weight, and length. The due date is June 22 and the doctor will usually try to induce labor if the baby hasn't arrived a week after the due date. Please write your own guess in the comments.

Here are the guesses we have so far:

Jeff
- date: June 17
- weight: 7 pounds 8 ounces
- length: 21 inches

Vanessa
- date: June 15
- weight: 7 pounds 7 ounces
- length: 21 inches

My mom's
- date: June 18
- weight: 7 pounds 6 ounces
- length: 21 inches

Vanessa's mom
- date: June 15
- weight: 6 pounds 15 ounces
- length: 19.5 inches

Vanessa's dad
- date: June 18
- weight: 8 pounds 6 ounces
- length: 20 inches

Sister
- date: June 15
- weight: 7 pounds 4 ounces
- length: 22 inches

The person who guesses the closest may receive a major award.

The Big Remodel

Over the past year, we've been remodeling our first house. It has been a very big job encompassing every room, and we did most of the work ourselves with help from family and friends. We hired out for some of the more complicated tasks, and we could not have done this without the help of many people (thank you!). I have a few hundred pictures of the entire remodeling process, so I thought it would make sense to show just a few pictures from the living room.

We began by removing all of the carpet in the house. In this first picture. you can see the front door as Vanessa is cleaning the floor. The rest of the pictures are taken from the front door (on the right) looking towards the back door (to the left).

When you first walked in the front door, you used to see this big structure which contained a couple of closets and was made of wood paneling. It created a short hallway which you would walk through to get to the living room from the front entry. We decided to remove this completely to create one great room.

After a significant amount of demolition, the closets are gone along with all of the wood paneling. Now you can see the old sliding glass doors in the back of the house from the front door. We replaced these with french doors. The water bottles are marking large nails embedded in the cement which we later cut out with a circular saw. (fun!)

Fast-forward ahead a few months, and we have hardwood floors, new drywall, paint, and we're moved in.

The master bedroom was actually the first room we finished, followed by the kitchen, then this, the living and dining room. I'll probably post more pictures at some point in the future. There are still a few details left to do, but the big remodel is basically finished and it feels very very good to be so close to completely done.

Not programming

So many posts related to programming recently. Time to change it up.

A Haiku

Tough to be funny,
because sometimes you fall flat.
Still it's worth trying.

A Fibo

Plain.
Bland.
Simple.
Serious.
Stay away from jokes.
Impress others with knowledge,
but sometimes it's dull.
Spice it up!
Let loose!
Try
puns.

A Joke

What do you call a joke that stinks?
Pungent.

A Better Joke

What's another name for a beach bum?
A tangent.

An Even Better Joke

What is equivalent to sine divided by cosine?
A beach bum.

See what I mean about falling flat ;-)

Creating and Using .so Files With gcc

And what is an .so file you might ask? Those from a Windows background might know them as .dll files, but that still doesn't answer the question.

Normally, when you compile a program, the system takes all of the pieces of code that you've written, converts them into something the computer can understand (machine code) and glues them together. You might compare the process to building a pyramid. All of the stones that you've sculpted are joined together and stacked up. Just like with a pyramid, if you want to change one of the stones, everything that sits on top of it needs to be adjusted. With a C program, making changes in a piece of code means lots of pieces need to be recompiled and reglued together.

If you use dynamic linking, shared libraries, whatever you'd like to call them, things work a bit differently. With dynamic linking, the pieces are not all glued together or stacked up, instead they are plugged in when they are needed. As a result, changes to a piece of code don't require that lots of other pieces get reshaped (recompiled) to fit. With dynamic linking, it is possible to change a piece of code while the program is running. Funny, that sounds a bit like a scripting language.

Here's an example. Let's say I wrote a library with a function called SpecialPrint. (It's like printf but different!) Here is the code for speciallib.c:

#include<stdio.h>

void SpecialPrint(char* payload) {
  printf("Special Print:%s\n", payload);
}

Now I write a program that uses this library. Here's the normal, non-dynamic, static linking, built like a pyramid way of using the library.

#include<stdio.h>
#include"speciallib.h"

int main() {
  printf("normal printf argument\n");
  SpecialPrint("special print's argument");
}

With the above code, I compile the SpecialPrint library with my main code and link them together, producing a single executable file. However, I can use the same speciallib file with code that loads the library dynamically while the program is running. The code might look something like this:

#include<stdio.h>
#include<dlfcn.h>

void ShowError() {
  char *dlError = dlerror();
  if(dlError) printf("Error with dl function: %s\n", dlError);
}

int main() {
  void *SharedObjectFile;
  void (*SpecialPrintFunction)(char*);

  // Load the shared libary;
  SharedObjectFile = dlopen("./speciallib.so", RTLD_LAZY);
  ShowError();
  // Obtain the address of a function in the shared library.
  SpecialPrintFunction = dlsym(SharedObjectFile, "SpecialPrint");
  ShowError();

  printf("normal printf argument\n");
  // Use the dynamically loaded function.
  (*SpecialPrintFunction)("special print's argument");

  dlclose(SharedObjectFile);
  ShowError();
}

In the above, the show error function is optional, I added it so that any errors that occur would be displayed. When you compile the above code, you'll need to make the speciallib into an .so file and make sure that the speciallib's directory (the current directory in my example) is listed as one of the places that we should look for shared object files. Here's what the steps to compile look like:

export LD_LIBRARY_PATH=`pwd`
gcc -c -fpic speciallib.c
gcc -shared -lc -o speciallib.so speciallib.o
gcc main.c -ldl

For an explanation of what the above compiler options mean, and further explanation on .so files, see these two IBM articles on using shared object files on Solaris and linux.

Learning about .so files has been very interesting to me, because they bring a new level of flexibility to a traditionally rigid environment like C.

Early vs Late Binding

I've been thinking recently about programming languages (surprised?), specifically about the things that make them different. One of the really nice things about C, is that it compiles into machine code which tends to run lean and mean. By that I mean it is blazing fast and doesn't take up much memory. On the other hand, programming in Python and JavaScript has really been growing on me. There is so much flexibility to create elegant solutions quickly and without rewriting lots of existing code. In fact, I'd say greater ability to reuse existing code is a natural outgrowth of programming language flexibility.

So where does this flexibility come from? One place I tend to notice it most, is in the ability to give an existing function a new body, in other words, you can plug in different behavior in place of the default.

Here's a simple example to illustrate the idea. Let's say that we created a simple checkout register which takes a receipt, adds the sales tax, and spits out the grand total. Here's our code foundation in both Python and JavaScript (these two examples do essentially the same thing):

Python:

def CalculateTax(amount):
  return amount * 0.18

class Receipt(object):
  
  def __init__(self, items=None):
    self.items = items or []
  
  def CalculateTotal(self):
    return sum([item + CalculateTax(item) for item in self.items])

JavaScript:

function calculateTax(amount) {
  return amount * 0.18;
}

function Receipt(items) {
  if (items) {
    this.items = items;
  } else {
    this.items = new Array();
  }
}

Receipt.prototype.calculateTotal = function() {
  var total = 0;
  for (var i = 0; i < this.items.length; i++) {
    total += this.items[i] + calculateTax(this.items[i]);
  }
  return total;
}

To use the above code, you might write something like this:

Python:

my_order = Receipt([5.50, 10, 7.89])
print my_order.CalculateTotal()

JavaScript:

var myOrder = new Receipt([5.50, 10, 7.89]);
alert(myOrder.calculateTotal());

Now let's say someone asks you to change the tax rate which is used when calculating the total. Here's the catch, you're not allowed to change the existing code. It turns out this is actually really easy. You can define a new function, then make an existing function name point to the new function. Here's an example of how to inject our new code:

Python:

def CalculateHigherTax(amount):
  return amount * 0.25

CalculateTax = CalculateHigherTax

print my_order.CalculateTotal()

JavaScript:

function calculateHigherTax(amount) {
  return amount * 0.25;
}

calculateTax = calculateHigherTax;

alert(myOrder.calculateTotal());

After adding the above code to the foundation we started with, you will notice that the calculate total method now uses calculate-higher-tax instead of the original function, even though you are calling the same method on the same object as before. Congratulations, you have just witnessed late binding in action.

So what is late binding? The idea is that the computer decides which code should be executed while the program is running. This seems normal in scripting languages, but compiled languages often use this too (I'm looking at you Java and C++). For example, overloaded methods and polymorphism take advantage of late binding. With late binding you can change the meaning of an identifier (for example, change the behavior when you call a specific function) at just about any time.

Now lets take a look at a language which uses early binding. C is a great example. With early binding, the meaning of things like function names are locked in when the code is compiled. There is no dynamic lookup while the program is running to see which code should be executed, instead the address of the desired code is embedded directly into the binary machine code.

Here is how the same calculate-total example might look in C:

#include<stdio.h>

float CalculateTax(float amount) {
  return amount * 0.18;
}

typedef struct {
  float* items;
  int num_items;
} Receipt;

float CalculateTotal(Receipt this_order) {
  int i;
  float total = 0;
  for(i = 0; i < this_order.num_items; i++) {
    total += this_order.items[i] + CalculateTax(this_order.items[i]);
  }
  return total;
}

int main(void) {
  Receipt my_order;
  float my_items[3] = {5.50, 10, 7.89};
  my_order.items = my_items;
  my_order.num_items = 3;
  printf("%f\n", CalculateTotal(my_order));
}

If you try to set CalculateTax to a new function definition, you will get an error at compile time because a function cannot be changed once it is bound. Early binding tends to produce more efficient programs. However, if you want to, you can still use the flexiblity available in late binding in C.

Using function pointers, you can store the address of the code that you want to be executed, and change the address while the program is running. We can achieve the same late binding effects that I've illustrated in Python and JavaScript by making some small changes to the C code (marked in bold below). Declare a function pointer named TaxCalculator which will store the address of the desired calculate-tax function, then change CalculateTotal so that it uses the TaxCalculator instead of directly calling a calculate-tax function.

#include<stdio.h>

float CalculateTax(float amount) {
  return amount * 0.18;
}

float CalculateHigherTax(float amount) {
  return amount * 0.25;
}

typedef struct {
  float* items;
  int num_items;
} Receipt;

float (*TaxCalculator)(float) = &CalculateTax;

float CalculateTotal(Receipt this_order) {
  int i;
  float total = 0;
  for(i = 0; i < this_order.num_items; i++) {
    total += this_order.items[i] + (*TaxCalculator)(this_order.items[i]);
  }
  return total;
}

int main(void) {
  Receipt my_order;
  float my_items[3] = {5.50, 10, 7.89};
  my_order.items = my_items;
  my_order.num_items = 3;
  printf("%f\n", CalculateTotal(my_order));
  TaxCalculator = &CalculateHigherTax;
  printf("%f\n", CalculateTotal(my_order));
}

There you have it!

Here's another way to think about this comparison. In high level languages which don't expose pointers, functions, variables, and other identifiers actually act like pointers.

Ubuntu Hardy Heron

Last week, I downloaded the beta release of Ubuntu 8.04 (Hardy Heron) to give it a try. I've been meaning to migrate our last Windows XP machine over to Linux for some time now (the other three computers I use regularly are Linux machines), but I've been reluctant to backup, repartition, and take the plunge. It seems like this is a common feeling among computer owners, but I think the Ubuntu community may have found an effective solution.

And the name of this new innovation: Wubi. Pop in the Ubuntu CD while running in Windows, and an auto-run installer opens which allows you to install Linux alongside Windows. When you reboot your computer, you see a menu of which operating system to boot into: Windows or Ubuntu. This means you can try out Ubuntu on your computer with zero risk to your existing files. In fact, you can access the files on your Windows installation from within Ubuntu. And if you decide Ubuntu is not your you, you can uninstall it as you would any other Windows program. Pretty slick.

Managing in the installation is just the beginning of the improvements the team has made. After I installed the latest version and booted into Ubuntu, it told me that there were propriety drivers for my NVIDIA graphics card and asked if I wanted to install them. I clicked the button, the download started, and I was up and running with 3D accelerated graphical desktop effects. I think I could sit there opening and closing windows all day. I'm looking forward to the upcoming official release.

A Musical Interlude... and back to Programming

I've been listening to Daft Punk and Justice quite a bit recently. Apparently I'm on a techno kick again. I've never found any electronic music that I've enjoyed as much as Joy Electric's The White Songbook. The purity of the tones and style has made it one of my all time favorite albums.

This got me thinking about a project which I thought of years ago, started, then abandoned. It was a music synthesizer/sequencer which you would program, by well, programming. I mean that the music would be controlled exclusively through a programming language. This would alter the creative process in several ways. Most music sequencers are graphical and allow you to lay out musical patterns in sequence. Writing a program is extremely non-linear, with classes, functions, and variables being defined in the code long before they are used. In this hypothetical sythesizer language. a composition might look something like this:

sequence "intro":
  playSample("beat", start=0:32.1, end=0:33.5, beats=[1,3,9,11,15])
  playSample("moog", beats=[5,7,11])
  shiftPitch(start=A4, end=C4, duration=bars(8))

sequence "solo":
  playSample("guitarRiff", start=1:15.3, end=2:09.0)

tempo 150 BPM
play("intro", now)
play("solo", end("intro"))
play("solo" now()+bars(5))

In the above example, the first play statement will be executed, then the third play statement (5 bars into the 8 bar intro), then the second solo will play again, probably before the first solo finishes. There are other interesting features in the pseudo-code above, but the fact that these sequences are played out of order was what I really want to highlight.

I've done live coding at several events over the years and I tend to have fun with it. It doesn't always go exactly as planned, but that is the whole idea. Live coding turns programming into a performance piece. I imagine there is a niche group of people who could really get into the live coding music scene.

XO Laptop

My XO laptop arrived in the mail recently and it is quite an amazing little machine. Conclusion up front: I'm extremely satisfied with it and in some ways this laptop computer is better than ones that sell for ten times the price.

You might recall from a previous post that I had downloaded the XO's operating system and taken it for a test drive in an emulator. Now I have the real thing in front of me, and it's safe to say that it is even better. After all, some of the most innovative features of this computer are in the hardware. My favorite feature is the screen. It is viewable in direct sunlight which makes it usable outdoors. Second up would be the wireless networking. The graphical network selector is fun to use and the connection tends to be more reliable than any of the other computers I've used with my home wireless router. The battery life is also impressive, easily five hours on a charge of its small battery. It even has a built-in camera and microphone.

It runs all of the software I need too. I used the instructions I wrote up when I installed firefox on the emulated operating system. Everything went smoothly and I was browsing the web using firefox in a few minutes (The XO laptop comes with a perfectly good web browser, but I wanted to use my favorite plugins and have more control over downloads).

I'm quite taken with the little machine. I've been using it as my primary computer at home, using it for all of the tasks I normally do (mostly browsing the web and programming). There are a couple of things that I would change if I had the chance. The first is the keyboard. It is an interesting design, made of a flexible rubber-like substance, and it works much better than other flexible keyboard that I've tried, but it took a while to get used to the shift key (I have to press in the corner of the key). The other difficulty is presented by the slower processor, but it doesn't get in my way most of the time. The only time I notice any slowness is when playing flash videos (like on YouTube). Perhaps part of the problem is flash for Linux, but I'm not sure. In any case, I don't really mind as I don't watch that much video, and if I want to, I have other computers that I can use.

It will probably come as no surprise that I wrote this post using the little green computer. I'm saddened by the end of the "give one get one" program, as I think there is still the opportunity for more people to donate and receive their own XO. If anyone is interested, it might be possible to order a batch of one hundred or more through the "give many" program.

BusyList

Andy and I started work on a simple little open source project for tracking tasks; it's called busylist. We wanted to experiment with Ajax, Python, and web service APIs, so we whipped up a basic system in a few hours. There is still quite a bit of work to be done, but it has been a great learning experience so far. An extremely alpha test version is available in subversion along with some instructions on the project's wiki pages. If you're interested, feel free to check it out (pun intended) and contribute if you like. It is an open source project after all.

(Portable) Ubuntu for Programmers

I've been trying over the past several weeks to find the best fit for Linux on a USB pen drive so that I can boot into my own operating system and get to my files no matter which computer I'm using. As you might notice from my other posts, I tend to spend quite a bit of my computer time in programming and browsing the Web, so the things I'm most interested in are a web browser (Firefox), support for wireless cards in several computers, and a variety of command line programming tools (gcc, python, vim, etc.). It should be possible to take one of the standard Linux distributions and install it on a USB drive (provided the drive is large enough), but I wanted to use a one gigabyte drive that I had, and with my simple needs I should really be able to get all of the necessities in under one gig. Along the way I've tried Puppy Linux, Slax, Feather Linux, DSL, and others, but I decided in the end to roll my own solution based on Ubuntu.

I'm a big fan of Ubuntu, but the standard desktop install is far too large for installation on a one gig drive. For a while I was using the live CD booting from a pen drive with a partition for my files. I used the instructions I found on Pen Drive Linux to set up the pen drive with the image from the live CD (only 750 megabytes). The only problem with this set-up was that all of my files were in a seperate partition and my home directory was wiped out each time. Since many Linux programs store settings in your home directory, this turned out to be a bit incovenient. I tried a few different options, but finally decided to go with a stripped down Ubunutu foundation and add the things I wanted.

I began with Ubuntu Server 7.10 and installed it on my USB drive using some of the recommendations in the installation instructions for low memory systems. During the installation process I selected guided partioning and I did not choose to install any of the software configurations in the "software to install" menu. After installing, I rebooted and added the following packages using sudo apt-get install:

lynx (optional)
screen (optional)
gcc (optional)
xorg
x-window-system-core
firefox

If you are using a laptop, you will likely want to install the following modules:

acpi
acpid

With the above installed you can check the battery's charge, remaining time, etc. by running acpi on the command line. For the graphical desktop window manager, I chose iceWM. I installed it by adding:

icewm
iceconf
icewm-themes

In the past I've worked quite a bit with Fluxbox as a window manager, but it seems like iceWM is easier to configure, especially under Ubuntu. The liQuid theme looks quite nice.

This set up boots into a text only command line mode because it is based on Ubuntu Server, to enter graphics mode, you simply run startx. I connected to my wireless network using wpa_supplicant and running iwconfig.

One of the benefits of working on a lightweight system on a flash drive is the bootup speed. In twenty seconds the computer boots from a cold start, connects to my wireless network, and enters the graphical desktop. I'm quite happy with my little portable operating system, and you probably won't be suprised to hear that I wrote this post using it.

In praise of Haikus

Programmers are no strangers to strict requirements on form and syntax, so working in the poetic medium of the Haiku comes almost naturally.

Programming is fun.
Little virtual widgets.
Poems that do work.

The brevity and compactness of the haiku lends itself well to writing something tighly focused. I find them quite enjoyable to write.

Of course, there are quite a few other poetic structures of note which can offer a fun challenge. The limerick and the sonnet are two of my favorites. Here's a limerick I wrote (beware, obscure programming reference ahead).

There once was a coder named Chuck.
And through all the source code he snuck.
  He changed not a line,
  it all worked just fine:
he programmed by punching a duck!

A sonnet would be a bit ambitious for this late hour. So unleash your creativity, let's see what you've got.

Happy Valentines Day

Vanessa prepared a wonderful meal for me this Valentines day. Four courses, the first one pictured here, all delicious. This was the roasted red pepper tomato soup with an artistic heart made of sour cream. And this was only the first course. Have I mentioned that the meal was delicious. I'm very thankful, I married quite a cook. Not only that but she decorated too.

It would seem I borrowed a page from one of Ben's blogs and wrote about food. What can I say, a meal like this makes an impression.

My Programming Journey so Far

One of the great things about working in computer science is that you never stop leaning. It seems that many programmer follow a progression from one popular language to the next, and I thought I'd dedicate a post to reminisce about my journey so far. I first learned to program in C. This was at the age of sometime around eleven or thirteen. I was instantly hooked, and since then, I've kept right on learning. I think the path I've taken has been fairly typical. From C, I learned C++ (starting in high school). I learned Java during a summer internship after my junior year of high school. In college, it was more C++, Java, and C (I really learned the ins and outs of C in my networking class) along with some other programming languages.

My favorite two classes in my college computer science curriculum were the ones in which I learned assembly language and designed an arithmetic logic unit and then a simple processor. I finally felt like I understood exactly how computers worked. With assembly language I learned a bit about machine code, how many clock cycles specific operations take, and it felt so good to optimize a bit of code to run blazingly fast. In circuit design I learned where those clock cycles come from, why operations take the time they do, and how those machine language op codes are determined. In all things software, at some point it all comes back to electronics.

College was also a time to get a taste of other, less widely used, but none-the-less important languages. Scheme and Prolog were particularly interesting to me, but I haven't had much occasion to use them very much recently.

Through my career, I've focused primarily on C++, then Java. After that I've had the opportunity to use a large number of languages. I learned Ajax programming using JavaScript, I wrote some PHP, C#, and a rather large amount of Python. Outside of work, I like to explore new concepts and languages and I've taken a look at some other languages too. Some notable examples include Ruby and Common Lisp, but I haven't built anything serious with them yet. Python is a language which I've really grabbed hold of recently and I've been learning quite a bit about it. At least half of the side projects I'm working on in my spare time these days are in Python. There seems to be quite a bit of momentum behind Python, and I'm very interested to see where this all goes.

So there you have it, a small glimpse into my journey thus far. How does it jive or differ from your own?

Firefox 3 Beta 2

I recently downloaded the second beta of Firefox 3 from Portable Apps. I didn't want to replace the version of Firefox I already had installed, so I used the version from Portable Apps which runs as a standalone binary. Sometimes it's really nice to unpack a program without touching the registry or worrying about installing.

Overall, I'm very happy with the changes I've seen in the latest version. I had heard that there have been some improvements to the JavaScript engine in this version, and they are noticeable. When I logged in to gmail it seemed a bit more responsive. I have to say though that my favorite changes are in the address bar. When typing the address, the address bar shows addresses, titles, and logos for pages that you've already visited. Firefox 2 did this too, but I think 3 gives more detail and a larger number of results. I found myself using it much more often than in 2. Part of the reason is that it shows the most recently visited page at the top instead of the shortest match. I also liked that you could star a URL to add it to your bookmarks, and you can even select a folder and tag the URL from within the address bar.

Programming Languages are Languages too

One of the reasons that people keep inventing new programming languages is that humans are good at using language and computers are not. So was we improve computers and add more complexity, programmers endeavor to make using these new features simpler and less painful. As a result, computer languages are moving in a general direction towards more natural human language. There will likely always be differences, but programming languages and human languages are strikingly similar if you understand some of the widely used syntax.

Here's an example. When you see something like this

z = x * y;
print(z);

it means that you want the computer to "store the value of x times y in the varibale z, then display z on the screen." As you can see, some programming syntax is borrowed from math. This example includes arithmetic and a function. Functions can also be though of as verbs, with variables as the nouns. In object oriented programming, variables can be nouns which are capable of performing actions. If you had a digital carrier pigeon, and you wanted to tell it to carry a letter to your grandmother's house, you might say something like:

myPidgeon.payload = myLetter;
myPideon.flyTo(grandma.house);

In human language, there are always multiple ways to say the same thing, and the same applies in programming. The programmer might just as easily design the program to give grandma the letter like this:

myLetter.setRecipient(grandma);
myPideon.deliver(myLetter);

Now for some fun. What do the following code snippets mean?

1. if (jack.getWorkPercent() == 100.0 &&
       jack.getPlayPercent() == 0.0) {
     jack.dullBoyFlag = true;
   }

2. Pie aPie = new Pie();
   Song aSong = new Song(sixpence);
   aSong.sing();
   fill(pocket, rye);
   aPie.add(new Blackbird()[24]);

3. Mouse mice[3];
   for (i in range(3)) {
     mice[i] = new BlindMouse();
   }
   observe(run(mice));
   

4. party = new Party(jack, jill);
   party.setTarget(water);
   party.equip(pail);
   party.ascend(hill);

A spoiled programmer

I've been writing quite a bit of Python code recently and I've become a bit spoiled. It's easy in Python to define new classes on the fly, create new functions, pass them here and there, and return arbitrary collections from a method. C will always have a special place in my heart (I think everyone's first language does), but I often think of ways I could make it a bit easier to do certain things like have functions that return functions or have a function return multiple values.

To explain by way of example, it would be fun to do something like this:

/* A function that returns multiple values */
int, char, int myFunction(int a, int b, int c, char d) {...}

...
  /* Invoke the function and store the results */
  int x, y;
  char c;
  {x, y, c} = myFunction(5, 6, 7, 'Z');

The above is a fairly Pythonic way of doing things, and it seems like it should be possible in C. The first way I thought of is using structs. I like to think of a struct as the precursor to a class. It allows the arbitrary grouping of variables into a single collection where they can be referred to by name. (In a couple of earlier posts, I showed how you could use structs to simulate classes in C.)

If I define a struct for each one of my multi-variable-returning functions, I can create functions which effectively return multiple values instead of just one. Yes, technically I am returning one value, the struct, but you know what I meant :-) Namely, if you look at the program's stack, there is probably no perceptible difference between returning a struct and returning multiple variables.

/* Create a 2 member struct to hold the return value */
struct myFuncReturn {
  int first;
  char second;
};

/* A function that returns an int and a char */
struct myFuncReturn myFunc(int a, int b, int c, char d) {
  struct myFuncReturn to_return;
  to_return.first = (a+b)*c;
  to_return.second = d;
  return to_return;
}

int main() {
  struct myFuncReturn pattern;
  pattern = myFunc(2, 3, 4, 'Z');
  printf("Pattern: %i, %c\n", pattern.first, pattern.second);
}

This works ok, but I would like to avoid having to create a new struct for each one of my functions. It might be easier if I didn't have to worry about types at all, so the natural choice is to have the function return a type-less void pointer (void*). The calling code would then be responsible for interpreting the function's return struct correctly. If I want to return a new anonymous struct from a function, it might look something like this:

void* myFunc(int a, int b, int c, char d);

If I use the above, I'll need to allocate memory for the struct and return it's address. This is a bit of a bother as well, because now I need to worry about cleaning up that memory later. Instead of having the function allocate a new structure to return, why not pass in a structure and have the function modify it? The code I would need to write would be more aesthetically pleasing (in my opinion) for both the function definition and the calling code which invokes it, and it might even be more efficient.

If I pass in a pointer to the result struct as the first parameter to the function, my program could look like this.

/* Function definition, the out parameter is the return value */
void myFunc(void* out, int a, int b, int c, char d) {
  ((struct{int first; char second;}*)out)->first = (a+b)*c;
  ((struct{int first; char second;}*)out)->second = d;
}

int main() {
  struct{int first; char second;} pattern;
  myFunc(&pattern, 2, 3, 4, 'Z');
  printf("Pattern: %i, %c\n", pattern.first, pattern.second);
}

Look ma, no type declarations! Now you might say that writing out the entire struct definition each time is a bit unpleasant, but you could always define a struct and use it instead. I wanted to show that you don't really need to declare a type for each function, which could create a bit of a mess if you start using multi-return functions everywhere. With the above pattern, you could also start to play some interesting games by having functions that actually return different structs in different situations (provided the out pointer's reserved space is large enough for the data you want to send back). If I've lost you by now, I do apologize.

For added effect, note that the anonymous structs don't need to match, you just need to make sure that the shape of the structure is the same so that you don't overwrite data. I could have written myFunc like this:

void myFunc(void* out, int a, int b, int c, char d) {
  ((struct{int first;}*)out)->first = (a+b)*c;
  ((struct{int x; char second;}*)out)->second = d;
}

Or if you want to go even further, like this:

void myFunc(void* out, int a, int b, int c, char d) {
  *((int*)out) = (a+b)*c;
  ((struct{int x; char second;}*)out)->second = d;
}

Ah, the joys of programming. It's little games like this that make programming lots of fun. It's like working on a big wide open puzzle that you get to build yourself. No wonder I'm spoiled.

Twitter

If you've never tried Twitter, it might just be worth your while. I've been using it for a few months now and I'm quite pleased. As much as I try to make frequent blog updates, writing an entire entry sometimes feel like a large task. In contrast, twitter imposes a strict 140 character limit. This limit is both challenging and freeing in some ways: How much can you pack into a sentence or two? In addition to providing a place to share small updates, Twitter introduces a social aspect as well. By using @username notation, you can let everyone know your post was directed to a specific person so that they have a window into the conversation.

If you are familiar with Facebook, using Twitter is a bit like having a website made of just your profile status and your wall. These are my two favorite features of Facebook, so perhaps this is why I enjoy Twitter. The main difference is that you never post on someone else's wall, your posts show up on their wall if they choose to "follow" you (subscribe to your updates). I've never really used my phone to twitter (yes twitter is also a verb) or receive updates, but supporting posts from multiple platforms is a big selling point for some users.

My Twitter page is here and I also include a feed viewer gadget here on my blog to display my last few Twitter posts. If you have an account post it below!

Trying out the XO Laptop Operating System

In a recent post I mentioned that I had ordered an XO Laptop from the One Laptop Per Child program. It is still on order but being the slightly impatient person that I am I decided to see if I could test drive the software on the laptop before it arrives. It is based on Linux after all which usually means the software is freely available somewhere on the Internet.

Taking the XO for a spin turned out to be pretty easy and I have been able to add all of the applications I've wanted so far. I mentioned in my last post about the XO that I wanted to use it for programming and web browsing so I had a few requirements in mind. The laptop comes preinstalled with a custom web browser and Python but I often like to program in C and C++ so I wanted to install gcc. The web browser has a few wrinkles too, in the development build I tested I wasn't able to get some flash plugins to load (could be the version of flash or the fact that the XO version I downloaded wasn't a production release). The browser is tabless and it is a bit difficult (though not impossible) to figure out where downloaded files are stored. In short it wasn't quite was I've grown accustomed to, so I thought I would try installing Firefox. He's my step by step instructions for trying out the XO Laptop virtually and customizing it.

I began with the XO's wiki and found out that there are instructions for emulating the XO and VMWare virtual machine images for recent builds of the system. VMWare is a program which creates a simulated computer that runs within your current operating system. For the past few years I've tested all of the Linux distributions I've considered on VMWare Server (free to download and use at home). Once I started VMWare, I opened the ship.2-OLPC-655.vmx file and started it up.

After the initial configuration, I wanted to add gcc, a collection of open source compilers. I thought it was going to involve downloading several RPM files, but I found out about a tool called yum which manages RPM packages. This is similar to Ubuntu's apt-get. As root I was able to run

yum install gcc

and it downloaded and installed all prerequisites.

Next I wanted to install Firefox, and to download it I thought I would try Lynx (a text based web browser). Installing Lynx was just as easy, as root I ran:

yum install lynx

I ran lynx www.google.com and searched for firefox and downloaded the tar.gz Linux version. After downloading I unpacked the archive using

tar zxvf firefox-2.0.0.11.tar.gz

I tried running firefox, but got an error about a missing shared object library. Yum was able to find this as well. One final time as root, I ran

yum install libstdc++.so.5

After installing the C++ library, firefox ran just fine. The menus and graphics in Firefox matched the XO's theme, which I thought was pretty nifty. I was also able to install Flash. Well there you have it, why not take it for a test drive yourself.

New Year's Resolutions

Well folks, it's that time of year again. Time to set goals with the best of intentions and aim high to better myself. I'm borrowing quite a few of my new years resolutions from last year, there were a couple that didn't go as well as I had hoped. Daily time for devotions, reading, and mediation tops the list. More frequently journaling and blogging also made the cut.

I noticed a handy goal tracking website on Lifehacker which I'm using at the moment. However, I often find that the online nature of tools used to track things like to-do lists and finances can create a small inconvenience which leads to an eventual breakdown. A plain old pen and paper still holds an important place.

In any case, here's to a new year and to best-laid plans.

An open source JavaScript library: q12

I've written some JavaScript utility functions as part of my ongoing wiki/note taking application. It is growing into a full fledged Ajax application with a web server and now a minimal Ajax library which I've decided to release as a separate open source project.

From the project's front page:

I found myself needing a few common utilities as I was writing an Ajax application. Rather than use a heavyweight or verbose library, I wanted something compact that minimized the amount of typing I needed to do. This is where the name q12 comes from, just three little keys up there in the upper left corner of the keyboard.

This library provides functions for the following:

• Basic DOM manipulation
• Asynchronous HTTP requests with callbacks
• Class methods and inheritance
• Base64 encoding and other forms of data escaping
• AES encryption

Writing your own Ajax library is also a great way to learn JavaScript (IMHO). I'll be making little tweaks as I work further on my project, it's getting quite close. I think I've probably said that before but rewriting from scratch tends to set one back a bit. Third iteration's the charm?