Posts in Category "Programming"

Want to Localize Your Flex/AIR Apps? It’s Easy! I’ll Show You How…Again!

For anyone who is interested in localizing their Flex or AIR applications, I’ve written a very simple series that I’ve contributed to the Adobe Developer Connection.  As I’ve mentioned before, localization may seem like an enormous task, for any application, but the Flex framework provides great utilities to make this process surprisingly easy!  The articles are part of a two-part series which focuses solely on the task of localizing Flex and AIR applications using the Flex framework.  I’ve previously talked about Part 1, but now Part 2 is published and the series is complete!

Localization in Flex – Part 1: Compiling resources into an application
Localization in Flex – Part 2: Loading resources at runtime

Here is the end-product of the tutorial, which you can emulate for yourself in your own applications!

The series covers a variety of ways to attack the task of localization.  Different approaches have different advantages as well as disadvantages, but with the complete series, you will hopefully have a better understanding of what approach will suit your needs and your customer’s needs.

Until next time, happy localizing!

C Puzzler – Give Me A Float

Time for another Puzzler! This time, let’s do a C Puzzler :) For those that don’t know what a Puzzler is, it is essentially a short problem used to demonstrate special cases or “features” of a particular language. Here is the format:

  1. Code – I introduce the code
  2. Question – I pose a multiple-choice question and you guess what the outcome is…think hard!
  3. Walkthrough – I walk through a reasonable explanation
  4. Answer – I tell you the real outcome (it might surprise you), and explain why
  5. Moral – How can we avoid making mistakes like this in our own code

Now that we all know what a Puzzler is, here is a simple C Puzzler:

Code:

// c-puzzler-give-me-a-float.c
#include <stdio.h>
 
int main()
{
	int x = 0.5 + giveMeAFloat();
 
	return x;
}
// c-puzzler-give-me-a-float-please.c
float giveMeAFloat()
{
	return 0.5;
}

Question:

What does this print?

  1. 0
  2. 1
  3. 1056964608
  4. it varies

Walkthrough:

There is a local variable, x, and it is declared as an int. It is being initialized to the sum of 0.5 and the value returned by the function giveMeAFloat, which is implemented in another source file. The function giveMeAFloat returns the float value 0.5, and so the sum of these two values is the float value 1.0. The variable x is an int, and so it will cast the value from 1.0 to 1. So, my answer is b, main returns the int value 1.

 

*SPOILER ALERT – ANSWER BELOW*


 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Answer:

The answer is actually d – it varies! But, in practice, you will likely get c – 1056964608. How does this happen? Well, the astute observer will notice that in the source file containing our main function, there is no function prototype declaring the function giveMeAFloat. Because of this, and the fact that giveMeAFloat is implemented in another source file, then giveMeAFloat is *assumed* to return an int and not a float! If the method were declared and defined within the same source file, the compiler would detect this error and not complete the compilation. However, due to separate compilation, this cast goes unnoticed. And so, because of this ambiguity, depending on the compiler and the platform, how this value is treated and stored will vary from machine to machine! To better understand this, let’s look at the practical case where the answer is 1056964608.

  • This assumes that the program is being executed on a typical machine setup, with an x86 architecture running a current version of gcc (v4.x+)
    When the program is executed, within main, an int variable, x, is declared and initialized with a simple assignment expression that invokes giveMeAFloat. When giveMeAFloat returns, it stores the value 0.5 into the return register, eax. Since we are on a little-endian machine, this value is 0x3F000000. However, since the compiler is expecting to read an integer value, it interprets 0x3F000000 as an int and not a float, effectively loading the value 1056964608 (this is the decimal interpretation of the floating point hex representation of 0x3F000000…yikes!). Back in main, the value 0.5 gets added to this, resulting in the float value 1056964608.5. This subsequently gets assigned to the variable x. Since x is an int, this value gets cast and therefore truncated to 1056964608. And so main returns 1056964608.
     

As you can see, there are many factors that can affect the return value. In particular, what value the compiler stores into the return register (if anything), how that value is stored internally (endian-ness of the host machine), and how that value is subsequently read from the register (interpreted as int, or float, or other) all play a part. Due to all of these factors, the return value from main is effectively unpredictable, and should be treated as such (regardless of what the practical case would yield)!

Moral:

Given an arbitrary name that has not yet been previously declared, if the name is followed by a left parenthesis, it is defined to be a function and it is assumed to return an int. To prevent this, explicitly declare the function, either as a function prototype at the top of the source file, like so…

#include <stdio.h>
 
float giveMeAFloat();
 
int main()
{
	int x = 0.5 + giveMeAFloat();
 
	return x;
}

…or within the calling routine, like so…

#include <stdio.h>
 
int main()
{
	float giveMeAFloat();
	int x = 0.5 + giveMeAFloat();
 
	return x;
}

Now, there is no confusion, to yourself or the compiler, about the return-type of the function giveMeAFloat().

That’s been another C Puzzler! Hope you enjoyed! Happy coding!

 

 
Charles

c-puzzler-give-me-a-float.zip (source code)

Update: This post was corrected based on some feedback in the comments by Mihai. Thanks for the feedback, Mihai!

My Adventure Writing My First Quine in Java

Today, I tried to write my very first quine. What is a quine, you might ask? Well, for those that don’t know, a quine is simply a program that takes no input but whose only output is the program code itself. Easy, right? That’s what I thought. This post is going to document my adventure writing my first quine in Java.

 

Trial and error

So, I need to write a program that outputs a program…itself to be exact. I didn’t think much of it, so I dove right in. Let’s take a look at my first pass…

public class Quine {
	public static void main(String[] args) {
		System.out.println("public class Quine {\n\tpublic static void main(String[] args) {\n\t\tSystem.out.println(\"...fuck");
	}
}
 
/* OUTPUT:
public class Quine {
	public static void main(String[] args) {
		System.out.println("...fuck
 
*/

Fuck. This won’t work. As you can see, the problem quickly reveals itself. Essentially, there comes a point where you must print the code that you are using to print! (Even that sentence is a little confusing) This can easily degrade into an infinite loop. So, how do you overcome this?

You must write some code that you use to both store the characters
to be printed, but can ALSO be used to print itself!

I believe this is the main problem to solve when writing quines. Once you can get over this hump, the rest is simple! If you can figure this out, you’ve done 90% of the work. Really! So I started to tackle this problem, head on.

 

A string that prints itself

First, I did away with the System.out.println() method. Instead, I opted for the printf() method. With functionality very similar to the ANSII C printf() method, it has some powerful string manipulation features that will make this quine much easier to write (and read). Second, I tried to think of a way to write some code that printed itself. More specifically, I decided that I needed to figure out a way to solve the following code segment…

String s = "?";
System.out.printf(?);

What could I replace the question marks with such that it would output the string declaration itself, exactly, and nothing else? I thought about this for a while before I came up with a solution. Since I think that this step is the most important and requires the most thinking, rather than ruin it for you, I’ll let you think about it for yourself.

 

*SPOILER ALERT – ANSWER BELOW*


 

 

 

 
Willard Van Orman Quine - A Harvard Professor of philosophy for which the self-reproducing code concept was named after

Willard Van Orman Quine - A Harvard professor of philosophy for which the self-reproducing code concept was named after



 

 

 

 

After some head-scratching, I came up with…

public class Quine {
	public static void main(String[] args) {
		String s = "String s = %c%s%c;";
		System.out.printf(s, '"', s, '"');
	}
}
 
/* OUTPUT:
String s = "String s = %c%s%c;";
*/

There are many other solutions for this, but this is what I came up with. Now that I’ve got this figured out, all that’s left is filling in the stuff before and after.

 

All that’s left is everything

The self-reproducing code that I wrote above is essentially the middle of the program, and I’ve figured out a way to print it. Now, on to printing the stuff that goes before. This is quite a bit simpler than the first step, but not quite trivial. Again, here is another failed attempt…

public class Quine {
	public static void main(String[] args) {
		String s = "public class Quine {\n\tpublic static void main(String[] args) {\n\t\tString s = %c%s%c;";
		System.out.printf(s, '"', s, '"');
	}
}
 
/* OUTPUT:
public class Quine {
	public static void main(String[] args) {
		String s = "public class Quine {
	public static void main(String[] args) {
		String s = %c%s%c;";
*/

You’ll notice that hardcoding the line-feeds and horizontal tabs into the string doesn’t give us the right result. They get evaluated by the printf() twice. The solution to this is to make use of the variable arguments in printf() and reference those characters instead.

public class Quine {
	public static void main(String[] args) {
		String s = "public class Quine {%c%cpublic static void main(String[] args) {%c%c%cString s = %c%s%c;";
		System.out.printf(s, '\n', '\t', '\n', '\t', '\t', '"', s, '"');
	}
}
 
/* OUTPUT:
public class Quine {
	public static void main(String[] args) {
		String s = "public class Quine {%c%cpublic static void main(String[] args) {%c%c%cString s = %c%s%c;";
*/

Nice! Things are coming along, but the code is getting uglier.

 

Spring cleaning!

As you can see, we’re starting to get a lot of redundancy in the printf() call. My next step was to clean this up. Quine’s are all about reuse! The less code there is, the less code I have to worry about re-printing. So, I changed all of the arguments to printf() to be index-based instead, allowing me to reuse characters.

public class Quine {
	public static void main(String[] args) {
		String s = "public class Quine {%3$c%4$cpublic static void main (String[] args) {%3$c%4$c%4$cString s = %2$c%1$s%2$c;";
		System.out.printf(s, s, '"', '\n', '\t');
	}
}
 
/* OUTPUT:
public class Quine {
	public static void main (String[] args) {
		String s = "public class Quine {%3$c%4$cpublic static void main (String[] args) {%3$c%4$c%4$cString s = %2$c%1$s%2$c;";
*/

This is looking a lot cleaner now. Finally, let’s round this quine off by filling in the rest of the code.

 

Print the rest...easy! I think.

Again, this is quite a bit simpler than the previous steps, but not trivial. Another failed attempt…

public class Quine {
	public static void main(String[] args) {
		String s = "public class Quine {%3$c%4$cpublic static void main (String[] args) {%3$c%4$c%4$cString s = %2$c%1$s%2$c;%3$c%4$c%4$cSystem.out.printf(s, s, ...fuck";
		System.out.printf(s, s, '"', '\n', '\t');
	}
}
 
/* OUTPUT:
public class Quine {
	public static void main (String[] args) {
		String s = "public class Quine {%3$c%4$cpublic static void main (String[] args) {%3$c%4$c%4$cString s = %2$c%1$s%2$c;%3$c%4$c%4$cSystem.out.printf(s, s, ...fuck";
		System.out.printf(s, s, ...fuck
*/

We have hit the familiar problem of printing code that is used to print itself! This is slightly different, however. The difference is that we are trying to output characters that must be escaped in one output, but not in the other. There is a simple solution for this! Use the ASCII character codes instead! Replacing ‘”‘, ‘\n’, and ‘\t’ with their ASCII decimal equivalent codes, we are easily able to insert them into the string literal without them being interpreted by the printf() method, and without the need for escaping them. In the end, we get….

public class Quine {
	public static void main(String[] args) {
		String s = "public class Quine {%3$c%4$cpublic static void main (String[] args) {%3$c%4$c%4$cString s = %2$c%1$s%2$c;%3$c%4$c%4$cSystem.out.printf(s, s, 34, 10, 9);%3$c%4$c}%3$c}";
		System.out.printf(s, s, 34, 10, 9);
	}
}
 
/* OUTPUT:
public class Quine {
	public static void main (String[] args) {
		String s = "public class Quine {%3$c%4$cpublic static void main (String[] args) {%3$c%4$c%4$cString s = %2$c%1$s%2$c;%3$c%4$c%4$cSystem.out.printf(s, s, 34, 10, 9);%3$c%4$c}%3$c}";
		System.out.printf(s, s, 34, 10, 9);
	}
}
*/

Eureka! My very first quine! Try writing one for yourself! Feel free to share them with me in the comments, or through e-mail at charlesb[at]adobe[dot]com! I’d love to post them :)

Enjoy!

 
Charles

JavaScript Puzzler – Let’s Print Some ZIP-Codes!

Let’s take a look at a JavaScript Puzzler. If you don’t know what a Puzzler is, it is essentially a short problem used to demonstrate a quirk or edge-case with the language that you might encounter. Here is the format:

  1. Code – I introduce the code
  2. Question – I pose a multiple-choice question and you guess what the outcome is…think hard!
  3. Walkthrough – I walk through a reasonable explanation
  4. Answer – I tell you the real outcome (it might surprise you), and explain why
  5. Moral – How can we avoid making mistakes like this in our own code

Now that we all know what a Puzzler is, here is a simple JavaScript Puzzler:

Code:

<script type="text/javascript">
 
	// array of 6 valid zip-codes
	var zipCodes = new Array("93021", "16284", "02392", "20341", "08163", "32959");
 
	// let's do something with each zip-code - for now, print them out
	for (i = 0; i < zipCodes.length; i++) {
 
		// sanity check
		if (!isNaN(parseInt(zipCodes[i])) && parseInt(zipCodes[i]) > 0) {
			document.write(parseInt(zipCodes[i]) + " ");
		}
 
	}
 
</script>

Question:

What does this print?

  1. 93021 16284 2392 20341 32959
  2. 93021 16284 2392 20341 8163 32959
  3. 93021 16284 20341 32959
  4. none of the above

Walkthrough:

So, we have an array of 6 ZIP-codes in string format. We iterate through each one and print it, but first we do a sanity check. Let’s walk through each number and see if it passes.

  • 93021 – This will return a number and it will be greater than 0, so “93021” will be written.
  • 16284 – This will return a number and it will be greater than 0, so “16284” will be written.
  • 02392- This number has a leading 0, but parseInt() will just trim it. So, this will also return a number greater than 0, and “2392” will also be printed (Note: no leading 0).
  • 20341 – This will return a number and it will be greater than 0, so “20341” will be written.
  • 08163 – The same as the other number with a leading 0, parseInt() will trim this and return valid number, so “8163” will be printed (Note again: no leading 0).
  • 32959 – This will return a number and it will be greater than 0, so “32959” will be written.

Therefore, we should see all six numbers printed, with the numbers that have trailing 0’s being trimmed. So, my answer is b, this code will print the string “93021 16284 2392 20341 8163 32959″.

 

*SPOILER ALERT – ANSWER BELOW*


 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Answer:

If you chose a, you were close. The answer is actually d – none of the above. This is because the ECMAScript standard does not define the interpretation of certain number literals, in particular number literals with a leading 0. Some JavaScript implementations will interpret these as integers with the leading 0 trimmed. Others will treat them as octal literals. It should be noted, though, that MOST JavaScript interpreters will perform the latter and interpret number literals with leading 0’s as octal literals. This is different from other languages, like Java’s Integer.parseInt(), which will conversely trim the leading 0.

So what actually gets printed? In most browsers, including IE 8, Firefox 3 and Chrome, the string “93021 16284 19 20341 32959″ gets printed (Notice the 19!). Let’s examine this step-by-step one more time…

  • 93021 – There is no leading 0, and so this number will get interpreted just as we expect, as the integer 93021, and so “93021” will be written.
  • 16284 – Again, no leading 0, so no surprises here. “16284” will be written.
  • 02392- This number has a leading 0, and so it will be interpreted as an octal literal. Notice, though, that the second least-significant-digit is a 9, which is not allowed in an octal number! And so, by the specification of parseInt(), it will read all digits until an illegal character is read. Therefore, parseInt() will parse the octal value 23, which equals ((2 x 8) + (3 * 1)) = (16 + 3) = 19 in decimal.
  • 20341 – This will return a number and it will be greater than 0, so “20341” will be written.
  • 08163 – Again, this number has a leading 0. But, this time, the most-significant-digit is an 8, which is also not allowed in an octal number. So, parseInt() will interpret the octal value 0, and return 0. This fails the second part of our sanity check (that our ZIP-code must be non-zero), and so this doesn’t get printed!
  • 32959 – This will get printed as is. No surprise here either.

Moral:

Whenever possible, do not write an integer with a leading zero. Doing so can cause unexpected behaviour across browsers with different JavaScript implementations. If you can’t control the input values (as in our example above), then make use of parseInt()’s second optional parameter, radix – e.g. use parseInt(“08163″, 10) to parse “08163” to a base-10 integer. Passing in the radix explicitly eliminates the variability between browser implementations.

That’s it for this JavaScript Puzzler! Until next time, happy coding!

Charles

javascript-puzzler-lets-print-some-zip-codes.zip (source code)

Want to Localize Your Flex/AIR Apps? It’s Easy! I’ll Show You How!

If you have an application or a website, and you’re targeting (or want to be targeting) an international audience, then you’re going to have to localize!  What that means is preparing your application for international use by building support for multiple languages.  It may sound like a daunting task, but the Flex framework makes it surprisingly easy.  I’ve written a very simple tutorial on the Adobe Developer Connection Flex Community that walks through a straightforward way of localizing a basic Flex application.

Localization in Flex – Part 1: Compiling resources into an application

Here is the end-product of the tutorial, which you can easily create yourself, or implement within your own existing project!

This tutorial is only part 1 of the series, and illustrates one common way to achieve localization.  There is another different, but common, way, which I’ll illustrate in part 2, and I’ll announce on this blog as well :)

Until next time, happy coding!

Update: I’ve just completed Part 2. Read about it here :)

C Puzzler – Like Java Puzzlers, but for C!

I’m a big fan of Java Puzzlers. If you’re not familiar with what those are, I highly encourage you to watch this Google Tech Talk by Joshua Bloch. In short, Java Puzzlers are quirky pitfalls and corner-cases one might encounter when programming with the Java language. I liked the concept so much, I thought I’d add a section on my blog for my own puzzlers! The format is simple:

  1. Code – I introduce the code
  2. Question - I pose a multiple-choice question and you guess what the outcome is…think hard!
  3. Walkthrough - I walk through a reasonable explanation
  4. Answer - I tell you the real outcome (it might surprise you), and explain why
  5. Moral - How can we avoid making mistakes like this in our own code

Now that we know what a Puzzler is, here is a simple C Puzzler:

Code:

/** c-puzzler-lets-get-funcy.c **/
#include <stdio.h>
 
int funcOne();
int funcTwo();
 
int x = 1;
 
int main()
{
	int y = funcOne() + funcTwo();
 
	return y;
}
 
int funcOne()
{
	return x;
}
 
int funcTwo()
{
	return ++x;
}

Question:

What value does main return?

  1. 2
  2. 3
  3. 4
  4. it varies

Walkthrough:

There is a global variable, x, and it is initialized to 1. In main(), there is a local variable, y, and it is initialized to the value returned by funcOne() plus the value returned by funcTwo(). The function funcOne() simply returns the value stored in variable x, which is 1. The function funcTwo() also references x, but increments it in the process. Since the increment operator is a prefix, it performs the increment before returning the value, and so funcTwo() will return the incremented value of x, which is 2. Therefore, y will equal 1 + 2, which is 3, and main() will return the int value 3. So, my answer is b, main will return 3.

 

*SPOILER ALERT – ANSWER BELOW*


 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Answer:

The answer is d – it varies. This is because in ANSI C, there is no guarantee as to the order in which the operands of an operator are evaluated. So, depending on the compiler implementation, funcOne() can be evaluated before funcTwo(), and vice versa, giving us a result of 3 or 4 depending on the compiler. It should be noted, though, that MOST C compilers will evaluate expressions of operands left to right, including the GNU compiler, but there is no guarantee that this is the case. As a result, the safest way to achieve compiler-agnostic results would be to use intermediary variables.

Moral:

The order in which operands of an operator is unspecified in C. So, to give safe and predictable results, external variables should be modified carefully, and specifically noted in the function’s documentation. If the documentation for a function is lacking, or you are working with a 3rd party API which, for all intents and purposes, is a black-box, use of intermediary variables to ensure order of operations is safest.

I hope you’ve enjoyed my first C Puzzler! Until next time, happy coding!

Charles

c-puzzler-lets-get-funcy.zip (source code)