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  • Why can't we capture the design of software more effectively?

    - by Ira Baxter
    As engineers, we all "design" artifacts (buildings, programs, circuits, molecules...). That's an activity (design-the-verb) that produces some kind of result (design-the-noun). I think we all agree that design-the-noun is a different entity than the artifact itself. A key activity in the software business (indeed, in any business where the resulting product artifact needs to be enhanced) is to understand the "design (the-noun)". Yet we seem, as a community, to be pretty much complete failures at recording it, as evidenced by the amount of effort people put into rediscovering facts about their code base. Ask somebody to show you the design of their code and see what you get. I think of a design for software as having: An explicit specification for what the software is supposed to do and how well it does it An explicit version of the code (this part is easy, everybody has it) An explanation for how each part of the code serves to achieve the specification A rationale as to why the code is the way it is (e.g., why a particualr choice rather than another) What is NOT a design is a particular perspective on the code. For example [not to pick specifically on] UML diagrams are not designs. Rather, they are properties you can derive from the code, or arguably, properties you wish you could derive from the code. But as a general rule, you can't derive the code from UML. Why is it that after 50+ years of building software, why don't we have regular ways to express this? My personal opinion is that we don't have good ways to express this. Even if we do, most of the community seems so focused on getting "code" that design-the-noun gets lost anyway. (IMHO, until design becomes the purpose of engineering, with the artifact extracted from the design, we're not going to get around this). What have you seen as means for recording designs (in the sense I have described it)? Explicit references to papers would be good. Why do you think specific and general means have not been succesful? How can we change this?

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  • Why a static main method in Java and C#, rather than a constructor?

    - by Konrad Rudolph
    Why did (notably) Java and C# decide to have a static method as their entry point – rather than representing an application instance by an instance of an Application class, with the entry point being an appropriate constructor which, at least to me, seems more natural? I’m interested in a definitive answer from a primary or secondary source, not mere speculations. This has been asked before. Unfortunately, the existing answers are merely begging the question. In particular, the following answers don’t satisfy me, as I deem them incorrect: There would be ambiguity if the constructor were overloaded. – In fact, C# (as well as C and C++) allows different signatures for Main so the same potential ambiguity exists, and is dealt with. A static method means no objects can be instantiated before so order of initialisation is clear. – This is just factually wrong, some objects are instantiated before (e.g. in a static constructor). So they can be invoked by the runtime without having to instantiate a parent object. – This is no answer at all. Just to justify further why I think this is a valid and interesting question: Many frameworks do use classes to represent applications, and constructors as entry points. For instance, the VB.NET application framework uses a dedicated main dialog (and its constructor) as the entry point1. Neither Java nor C# technically need a main method. Well, C# needs one to compile, but Java not even that. And in neither case is it needed for execution. So this doesn’t appear to be a technical restriction. And, as I mentioned in the first paragraph, for a mere convention it seems oddly unfitting with the general design principle of Java and C#. To be clear, there isn’t a specific disadvantage to having a static main method, it’s just distinctly odd, which made me wonder if there was some technical rationale behind it. I’m interested in a definitive answer from a primary or secondary source, not mere speculations. 1 Although there is a callback (Startup) which may intercept this.

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  • C/C++: Who uses the logical operator macros from iso646.h and why?

    - by Jaime Soto
    There has been some debate at work about using the merits of using the alternative spellings for C/C++ logical operators in iso646.h: and && and_eq &= bitand & bitor | compl ~ not ! not_eq != or || or_eq |= xor ^ xor_eq ^= According to Wikipedia, these macros facilitate typing logical operators in international (non-US English?) and non-QWERTY keyboards. All of our development team is in the same office in Orlando, FL, USA and from what I have seen we all use the US English QWERTY keyboard layout; even Dvorak provides all the necessary characters. Supporters of using the iso646.h macros claim we should them because they are part of the C and C++ standards. I think this argument is moot since digraphs and trigraphs are also part of these standards and they are not even supported by default in many compilers. My rationale for opposing these macros in our team is that we do not need them since: Everybody on our team uses the US English QWERTY keyboard layout; C and C++ programming books from the US barely mention iso646.h, if at all; and new developers may not be familiar with iso646.h (this is expected if they are from the US). /rant Finally, to my set of questions: Does anyone in this site use the iso646.h logical operator macros? Why? What is your opinion about using the iso646.h logical operator macros in code written and maintained on US English QWERTY keyboards? Is my digraph and trigraph analogy a valid argument against using iso646.h with US English QWERTY keyboard layouts? EDIT: I missed two similar questions in StackOverflow: Is anybody using the named boolean operators? Which C++ logical operators do you use: and, or, not and the ilk or C style operators? why?

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  • Memory concerns while plotting escape from DLL Hell in Delphi

    - by Peter Turner
    I work on a program with about 50 DLLs that are loaded from one executable, it's an old organically grown program where the only rationale for creating a new DLL is that one previously didn't exist to fill a given need. (and namespaces didn't exist in Delphi so it never crossed our mind to make dll1.main.pas, dll2.main.pas or something even more unique) What we want to do is consolidate all these DLLs into one executable, since none of them are used out of the program, there shouldn't be much of a problem. The concern my boss has is that if we did this, the memory overhead for terminal server clients would go through the roof. So, I've stepped through enough initialization code to know that lots of stuff is done every time a DLL is loaded in to memory, but say I've got a project with about 4000 files, and 50 dlls, 10 of which are probably utilized by any one user in any one session of the program. The 50 dlls are about 2/3rds form files, if not more, but beyond that there's not a lot of other resources being loaded (only a few embedded pictures, icons, cursors, etc..). If I loaded all these files in to memory, how much memory is used per unit? how much is used per class? How do I keep the overhead down? and what is the biggest project one can reasonably expect to build with Delphi? This tidbit won't help answering, but I think it might clarify what my boss is worried about, we currently start our program at about 18megs, normal working conditions are usually less than 40 megs, he thinks it could climb as high as 120 megs.

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  • Explanation on how "Tell, Don't Ask" is considered good OO

    - by Pubby
    This blogpost was posted on Hacker News with several upvotes. Coming from C++, most of these examples seem to go against what I've been taught. Such as example #2: Bad: def check_for_overheating(system_monitor) if system_monitor.temperature > 100 system_monitor.sound_alarms end end versus good: system_monitor.check_for_overheating class SystemMonitor def check_for_overheating if temperature > 100 sound_alarms end end end The advice in C++ is that you should prefer free functions instead of member functions as they increase encapsulation. Both of these are identical semantically, so why prefer the choice that has access to more state? Example 4: Bad: def street_name(user) if user.address user.address.street_name else 'No street name on file' end end versus good: def street_name(user) user.address.street_name end class User def address @address || NullAddress.new end end class NullAddress def street_name 'No street name on file' end end Why is it the responsibility of User to format an unrelated error string? What if I want to do something besides print 'No street name on file' if it has no street? What if the street is named the same thing? Could someone enlighten me on the "Tell, Don't Ask" advantages and rationale? I am not looking for which is better, but instead trying to understand the author's viewpoint.

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  • An experiment: unlimited free trial

    - by Alex.Davies
    The .NET Demon team have just implemented an experiment that is quite a break from Red Gate's normal business model. Instead of the tool expiring after the trial period, it now continues to work, but with a new message that appears after the tool has saved you a certain amount of time. The rationale is that a user that stops using .NET Demon because the trial expired isn't doing anyone any good. We'd much rather people continue using it forever, as long as everyone that finds it useful and can afford it still pays for it. Hopefully the message appearing is annoying enough to achieve that, but not for people to uninstall it. It's true that many companies have tried it before with mixed results, but we have a secret weapon. The perfect nag message? The neat thing for .NET Demon is that we can easily measure exactly how much time .NET Demon has saved you, in terms of unnecessary project builds that Visual Studio would have done. When you press F5, the message shows you the time saved, and then makes you wait a shorter time before starting your application. Confronted with the truth about how amazing .NET Demon is, who can do anything but buy it? The real secret though, is that while you wait, .NET Demon gives you entertainment, in the form of a picture of a cute kitten. I've only had time to embed one kitten so far, but the eventual aim is for a random different kitten to appear each time. The psychological health benefits of a dose of kittens in the daily life of the developer are obvious. My only concern is that people will complain after paying for .NET Demon that the kittens are gone.

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  • How to set up VirtualBox Bridged Network on Windows 7 Host?

    - by Tong Wang
    I have virtualbox running on a Windows 2008 server, with a guest running ubuntu 10.04. The ubuntu guest is given a static IP of 192.168.1.4, which also has openssh installed. The guest has bridged network setup, I can ping 192.168.1.4 from any machine in the LAN, the ubuntu guest can also access the LAN. However, when I try to PuTTY into the ubuntu machine, I always get "connection refused". Below are some setup details: ubuntu IP: 192.168.1.4 hosts.allow sshd : 192.168.1.38 hosts.deny ALL : ALL when I the following command, I can see that sshd is listening on port 22: lsof -i tcp:22 Any idea? EDIT: It turned out to be a wrong VirtualBox Bridged Network setup. I give the Ubuntu guest a static IP of 192.168.1.4 (assigned to eth0). Then in the Windows 7 host, in the Network and Sharing Center, there is a new connection named "VirtualBox Host-Only Network" after the bridge is setup, that connection is again given the same static IP of 192.168.1.4. Once I change the "VirtualBox Host-Only Network" to automatically obtain an IP address, it's getting a different IP address of 169.254.249.70(Tentative). And now I can SSH into 192.168.1.4 with no problem, even without touching hosts.allow and hosts.deny. I've also noticed that in the properties windows (see screenshot below) of the "VirtualBox Host-Only Network", the second checkbox, "VirtualBox Bridged Networking Driver" is unchecked. While the same checkbox of the physical NIC (that is bridged to) is checked. So my further question is: is this how VBox bridged networking supposed to be setup? Any rationale behind this? I'd appreciate if someone could provide some explaination on VBox bridged networking setup on Windows host and I'll accept it as an answer.

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  • Using Clojure instead of Python for scalability (multi core) reasons, good idea?

    - by Vandell
    After reading http://clojure.org/rationale and other performance comparisons between Clojure and many languages, I started to think that apart from ease of use, I shouldn't be coding in Python anymore, but in Clojure instead. Actually, I began to fill irresponsisble for not learning clojure seeing it's benefits. Does it make sense? Can't I make really efficient use of all cores using a more imperative language like Python, than a lisp dialect or other functional language? It seems that all the benefits of it come from using immutable data, can't I do just that in Python and have all the benefits? I once started to learn some Common Lisp, read and done almost all exercices from a book I borrowod from my university library (I found it to be pretty good, despite it's low popularity on Amazon). But, after a while, I got myself struggling to much to do some simple things. I think there's somethings that are more imperative in their nature, that makes it difficult to model those thins in a functional way, I guess. The thing is, is Python as powerful as Clojure for building applications that takes advantages of this new multi core future? Note that I don't think that using semaphores, lock mechanisms or other similar concurrency mechanism are good alternatives to Clojure 'automatic' parallelization.

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  • An experiment: unlimited free trial

    - by Alex.Davies
    The .NET Demon team have just implemented an experiment that is quite a break from Red Gate's normal business model. Instead of the tool expiring after the trial period, it now continues to work, but with a new message that appears after the tool has saved you a certain amount of time. The rationale is that a user that stops using .NET Demon because the trial expired isn't doing anyone any good. We'd much rather people continue using it forever, as long as everyone that finds it useful and can afford it still pays for it. Hopefully the message appearing is annoying enough to achieve that, but not for people to uninstall it. It's true that many companies have tried it before with mixed results, but we have a secret weapon. The perfect nag message? The neat thing for .NET Demon is that we can easily measure exactly how much time .NET Demon has saved you, in terms of unnecessary project builds that Visual Studio would have done. When you press F5, the message shows you the time saved, and then makes you wait a shorter time before starting your application. Confronted with the truth about how amazing .NET Demon is, who can do anything but buy it? The real secret though, is that while you wait, .NET Demon gives you entertainment, in the form of a picture of a cute kitten. I've only had time to embed one kitten so far, but the eventual aim is for a random different kitten to appear each time. The psychological health benefits of a dose of kittens in the daily life of the developer are obvious. My only concern is that people will complain after paying for .NET Demon that the kittens are gone.

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  • Free Webinar: A faster, cheaper, better IT Department with Azure

    - by Herve Roggero
    Join me for a free Webinar on Wednesday October 17th at 1:30PM, Eastern Time. I will discuss the benefits of cloud computing with the Azure platform. There isn’t a company out there that would say “No” to reduced IT costs and unlimited scaling bandwidth. This webinar will focus on the specific benefits of the Microsoft Azure cloud platform and will convince you on the sound business rationale behind moving to the cloud. From Infrastructure as a Service (Iaas) to Platform as a Service (Paas), Azure supports quick deployments, virtual machines, native SQL Databases and much more. Topics that will be discussed: - Why use Azure for your Cloud Computing needs - Iaas and Paas Offerings - Differing project approaches to Cloud computing - How Azure’s agility and reduced costs lead to better solutions Attendees of this webinar will also be eligible to receive the following: Free Two Hour Consultation which can include: - Review of Your Cloud Strategy - Cloud Roadmap Review - Review of Data-mart strategies - Review of Mobility Strategies Click Here to Register Now. About Herve Roggero Hervé Roggero, Azure MVP, is the founder of Blue Syntax Consulting, a company specialized in cloud computing products and services. Hervé's experience includes software development, architecture, database administration and senior management with both global corporations and startup companies. Hervé holds multiple certifications, including an MCDBA, MCSE, MCSD. He also holds a Master's degree in Business Administration from Indiana University. Hervé is the co-author of "PRO SQL Azure" from Apress. For more information, visit www.bluesyntax.net.

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  • An experiment: unlimited free trial

    - by Alex Davies
    The .NET Demon team have just implemented an experiment that is quite a break from Red Gate’s normal business model. Instead of the tool expiring after the trial period, it now continues to work, but with a new message that appears after the tool has saved you a certain amount of time. The rationale is that a user that stops using .NET Demon because the trial expired isn’t doing anyone any good. We’d much rather people continue using it forever, as long as everyone that finds it useful and can afford it still pays for it. Hopefully the message appearing is annoying enough to achieve that, but not for people to uninstall it. It’s true that many companies have tried it before with mixed results, but we have a secret weapon. The perfect nag message? The neat thing for .NET Demon is that we can easily measure exactly how much time .NET Demon has saved you, in terms of unnecessary project builds that Visual Studio would have done. When you press F5, the message shows you the time saved, and then makes you wait a shorter time before starting your application. Confronted with the truth about how amazing .NET Demon is, who can do anything but buy it? The real secret though, is that while you wait, .NET Demon gives you entertainment, in the form of a picture of a cute kitten. I’ve only had time to embed one kitten so far, but the eventual aim is for a random different kitten to appear each time. The psychological health benefits of a dose of kittens in the daily life of the developer are obvious. My only concern is that people will complain after paying for .NET Demon that the kittens are gone.

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  • Is there a website that scrapes job postings to determine the popularity of web technologies? [closed]

    - by dB'
    I'm often in a position where I need to choose between a number of web technologies. These technologies might be programming languages, or web application frameworks, or types of databases, or some other kind of toolkit used by programmers. More often than not, after some doing research, I end up with a list of contenders that are all equally viable. They're all powerful enough to solve my problem, they're all popular and well supported, and they're all equally familiar/unfamiliar to me. There's no obvious rationale by which to choose between them. Still, I need to pick one, so at this point I usually ask myself a hypothetical question: which one of these technologies, if I invest in learning it, would be most helpful to me in a job search? Where can I go on the internet to answer this question? Is there a website/service that scrapes the texts of worldwide job postings and would allow me to compare, say, the number of employers looking for expertise in technology x vs. technology y? (Where x and y are Rails vs. Djando, Java vs. Python, Brainfuck vs. LOLCode, etc.)

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  • How can I convince my boss that ANSI C is inadequate for our new project?

    - by justifiably cowardly
    A few months ago, we started developing an app to control an in-house developed test equipment and record a set of measurements. It should have a simple UI, and would likely require threads due to the continuous recording that must take place. This application will be used for a few years, and shall be maintained by a number of computer science students during this period. Our boss graduated some 30 years ago (not to be taken as an offense; I have more than half that time on my back too) and has mandated that we develop this application in ANSI C. The rationale is that he is the only one that will be around the entire time, and therefore he must be able to understand what we are doing. He also ruled that we should use no abstract data types; he even gave us a list with the name of the global variables (sigh) he wants us to use. I actually tried that approach for a while, but it was really slowing me down to make sure that all pointer operations were safe and all strings had the correct size. Additionally, the number of lines of code that actually related to the problem in hand was a only small fraction of our code base. After a few days, I scrapped the entire thing and started anew using C#. Our boss has already seen the program running and he likes the way it works, but he doesn't know that it's written in another language. Next week the two of us will meet to go over the source code, so that he "will know how to maintain it". I am sort of scared, and I would like to hear from you guys what arguments I could use to support my decision. Cowardly yours,

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  • Open-sourcing a proprietary library without certain features

    - by nha
    I hope I'm in the right place to ask that. I have a question regarding the practice of open-sourcing a proprietary library that we built and use at work. The licence will probably be MIT. I like the idea, but here comes the unusual part : I have been tasked to remove some of the most advanced features. Those will remain on our servers, available as a service. We will open-source the (JavaScript in case it is of interest) library, along with a minimal associated server code. I am not asking a question about the technical problems (I imagine we will have to maintain and synchronize somehow different repositories, maybe with incompatible pull requests, but this for stack overflow). What I would like to know is: How that would be perceived by the community at large ? Does it risk killing the eventual interest in this library? I don't personally know of any library that works like that. I'm pretty sure it is possible however, but any evidence of such a library is welcome (successful if possible). That's also because I'd like to see how they present it. More importantly, what could be the rationale for/against it? I'm not sure I understand the consequences of doing it so.

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  • Paying great programmers more than average programmers

    - by Kelly French
    It's fairly well recognized that some programmers are up to 10 times more productive than others. Joel mentions this topic on his blog. There is a whole blog devoted to the idea of the "10x productive programmer". In years since the original study, the general finding that "There are order-of-magnitude differences among programmers" has been confirmed by many other studies of professional programmers (Curtis 1981, Mills 1983, DeMarco and Lister 1985, Curtis et al. 1986, Card 1987, Boehm and Papaccio 1988, Valett and McGarry 1989, Boehm et al 2000). Fred Brooks mentions the wide range in the quality of designers in his "No Silver Bullet" article, The differences are not minor--they are rather like the differences between Salieri and Mozart. Study after study shows that the very best designers produce structures that are faster, smaller, simpler, cleaner, and produced with less effort. The differences between the great and the average approach an order of magnitude. The study that Brooks cites is: H. Sackman, W.J. Erikson, and E.E. Grant, "Exploratory Experimental Studies Comparing Online and Offline Programming Performance," Communications of the ACM, Vol. 11, No. 1 (January 1968), pp. 3-11. The way programmers are paid by employers these days makes it almost impossible to pay the great programmers a large multiple of what the entry-level salary is. When the starting salary for a just-graduated entry-level programmer, we'll call him Asok (From Dilbert), is $40K, even if the top programmer, we'll call him Linus, makes $120K that is only a multiple of 3. I'd be willing to be that Linus does much more than 3 times what Asok does, so why wouldn't we expect him to get paid more as well? Here is a quote from Stroustrup: "The companies are complaining because they are hurting. They can't produce quality products as cheaply, as reliably, and as quickly as they would like. They correctly see a shortage of good developers as a part of the problem. What they generally don't see is that inserting a good developer into a culture designed to constrain semi-skilled programmers from doing harm is pointless because the rules/culture will constrain the new developer from doing anything significantly new and better." This leads to two questions. I'm excluding self-employed programmers and contractors. If you disagree that's fine but please include your rationale. It might be that the self-employed or contract programmers are where you find the top-10 earners, but please provide a explanation/story/rationale along with any anecdotes. [EDIT] I thought up some other areas in which talent/ability affects pay. Financial traders (commodities, stock, derivatives, etc.) designers (fashion, interior decorators, architects, etc.) professionals (doctor, lawyer, accountant, etc.) sales Questions: Why aren't the top 1% of programmers paid like A-list movie stars? What would the industry be like if we did pay the "Smart and gets things done" programmers 6, 8, or 10 times what an intern makes? [Footnote: I posted this question after submitting it to the Stackoverflow podcast. It was included in episode 77 and I've written more about it as a Codewright's Tale post 'Of Rockstars and Bricklayers'] Epilogue: It's probably unfair to exclude contractors and the self-employed. One aspect of the highest earners in other fields is that they are free-agents. The competition for their skills is what drives up their earning power. This means they can not be interchangeable or otherwise treated as a plug-and-play resource. I liked the example in one answer of a major league baseball team trying to field two first-basemen. Also, something that Joel mentioned in the Stackoverflow podcast (#77). There are natural dynamics to shrink any extreme performance/pay ranges between the highs and lows. One is the peer pressure of organizations to pay within a given range, another is the likelyhood that the high performer will realize their undercompensation and seek greener pastures.

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  • Simple python oo issue

    - by Alex K
    Hello, Have a look a this simple example. I don't quite understand why o1 prints "Hello Alex" twice. I would think that because of the default self.a is always reset to the empty list. Could someone explain to me what's the rationale here? Thank you so much. class A(object): def __init__(self, a=[]): self.a = a o = A() o.a.append('Hello') o.a.append('Alex') print ' '.join(o.a) # >> prints Hello Alex o1 = A() o1.a.append('Hello') o1.a.append('Alex') print ' '.join(o1.a) # >> prints Hello Alex Hello Alex

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  • SCJP question: Method ambiguous

    - by Markos Fragkakis
    Take a look at this code: public class Test { public static void main(String... args) { flipFlop("hello", new Integer(4), 2004); // flipFlop("hello", 10, 2004); // this works! } private static void flipFlop(String str, int i, Integer iRef) { System.out.println(str + " (String, int, Integer)"); } private static void flipFlop(String str, int i, int j) { System.out.println(str + " (String, int, int)"); } } The compiler gives an error that the invocation is ambiguous: Description Resource Path Location Type The method flipFlop(String, int, Integer) is ambiguous for the type Test Test.java scjp19 - inheritence/src line 3 Java Problem But if the commented-out line is used ti invoke flip-flop, the method is unambiguously invoked (the second one, because autoboxing comes after using the primitive itself). I would expect the compiler to see that the second argument will be unboxed one way or the other, and judge what method must be invoked depending on the third argument. Why does not this happen? What is the rationale?

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  • C question: Padding bits in unsigned integers and bitwise operations (C89)

    - by Anonymous Question Guy
    I have a lot of code that performs bitwise operations on unsigned integers. I wrote my code with the assumption that those operations were on integers of fixed width without any padding bits. For example an array of 32 bit unsigned integers of which all 32 bits available for each integer. I'm looking to make my code more portable and I'm focused on making sure I'm C89 compliant (in this case). One of the issues that I've come across is possible padded integers. Take this extreme example, taken from the GMP manual: However on Cray vector systems it may be noted that short and int are always stored in 8 bytes (and with sizeof indicating that) but use only 32 or 46 bits. The nails feature can account for this, by passing for instance 8*sizeof(int)-INT_BIT. I've also read about this type of padding in other places. I actually read of a post on SO last night (forgive me, I don't have the link and I'm going to cite something similar from memory) where if you have, say, a double with 60 usable bits the other 4 could be used for padding and those padding bits could serve some internal purpose so they cannot be modified. So let's say for example my code is compiled on a platform where an unsigned int type is sized at 4 bytes, each byte being 8 bits, however the most significant 2 bits are padding bits. Would UINT_MAX in that case be 0x3FFFFFFF (1073741823) ? #include <stdio.h> #include <stdlib.h> /* padding bits represented by underscores */ int main( int argc, char **argv ) { unsigned int a = 0x2AAAAAAA; /* __101010101010101010101010101010 */ unsigned int b = 0x15555555; /* __010101010101010101010101010101 */ unsigned int c = a ^ b; /* ?? __111111111111111111111111111111 */ unsigned int d = c << 5; /* ?? __111111111111111111111111100000 */ unsigned int e = d >> 5; /* ?? __000001111111111111111111111111 */ printf( "a: %X\nb: %X\nc: %X\nd: %X\ne: %X\n", a, b, c, d, e ); return 0; } is it safe to XOR two integers with padding bits? wouldn't I XOR whatever the padding bits are? I can't find this behavior covered in C89. furthermore is the c var guaranteed to be 0x3FFFFFFF or if for example the two padding bits were both on in a or b would c be 0xFFFFFFFF ? same question with d and e. am i manipulating the padding bits by shifting? I would expect to see this below, assuming 32 bits with the 2 most significant bits used for padding, but I want to know if something like this is guaranteed: a: 2AAAAAAA b: 15555555 c: 3FFFFFFF d: 3FFFFFE0 e: 01FFFFFF Also are padding bits always the most significant bits or could they be the least significant bits? Thanks guys EDIT 12/19/2010 5PM EST: Christoph has answered my question. Thanks! I had also asked (above) whether padding bits are always the most significant bits. This is cited in the rationale for the C99 standard, and the answer is no. I am playing it safe and assuming the same for C89. Here is specifically what the C99 rationale says for §6.2.6.2 (Representation of Integer Types): Padding bits are user-accessible in an unsigned integer type. For example, suppose a machine uses a pair of 16-bit shorts (each with its own sign bit) to make up a 32-bit int and the sign bit of the lower short is ignored when used in this 32-bit int. Then, as a 32-bit signed int, there is a padding bit (in the middle of the 32 bits) that is ignored in determining the value of the 32-bit signed int. But, if this 32-bit item is treated as a 32-bit unsigned int, then that padding bit is visible to the user’s program. The C committee was told that there is a machine that works this way, and that is one reason that padding bits were added to C99. Footnotes 44 and 45 mention that parity bits might be padding bits. The committee does not know of any machines with user-accessible parity bits within an integer. Therefore, the committee is not aware of any machines that treat parity bits as padding bits. EDIT 12/28/2010 3PM EST: I found an interesting discussion on comp.lang.c from a few months ago. Bitwise Operator Effects on Padding Bits (VelocityReviews reader) Bitwise Operator Effects on Padding Bits (Google Groups alternate link) One point made by Dietmar which I found interesting: Let's note that padding bits are not necessary for the existence of trap representations; combinations of value bits which do not represent a value of the object type would also do.

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  • Using local classes with STL algorithms

    - by David Rodríguez - dribeas
    I have always wondered why you cannot use locally defined classes as predicates to STL algorithms. In the question: Approaching STL algorithms, lambda, local classes and other approaches, BubbaT mentions says that 'Since the C++ standard forbids local types to be used as arguments' Example code: int main() { int array[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 }; std::vector<int> v( array, array+10 ); struct pair : public std::unary_function<int,bool> { bool operator()( int x ) { return !( x % 2 ); } }; std::remove_if( v.begin(), v.end(), pair() ); // error } Does anyone know where in the standard is the restriction? What is the rationale for disallowing local types?

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  • Why do C# automatic properties not support default values like VB 2010?

    - by Rob van Groenewoud
    Looking at the new VB 2010 features, I stumbled upon support for Auto-Implemented Properties. Since I'm working with C#, this seemed quite familiar, but I noticed that VB did add a feature I would love to have in C#: setting a arbitrary default value for the auto-implemented property: I really like the clean usage of auto-properties in C#. This would save us the effort of introducing a backing field and hooking it up to the property everytime we simply need a default value, thereby cluttering up the code unnecessarily. I was wondering why this wasn't introduced in C# as well? What could be the rationale for not doing this? Is a syntax discussion going on, or are there technical limitations to implementing this?

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  • Visualize compiler warnings

    - by christoffer
    I'm looking for a way to visualize compiler warnings and remarks, by annotating or otherwise showing which lines cause a report. This is much like a modern IDE like NetBeans or Eclipse already does, but I'd like to take output from several compilers (and other static code analysis tools) at once, and create one single annotation in order to get a better overview. The rationale is that we've seen some problems go completely undetected by, say, Visual Studio 2005, but accurately detected with a proprietary ARM compiler, and vice versa. Cross-referencing warnings could potentially locate problems better, but doing so completely manually is infeasible. Have you heard of such a tool? Could an open-source IDE like Eclipse be extended to use several compilers at once, or has it already been done?

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  • Storing credit card details

    - by Andrew
    I have a business requirement that forces me to store a customer's full credit card details (number, name, expiry date, CVV2) for a short period of time. Rationale: If a customer calls to order a product and their credit card is declined on the spot you are likely to lose the sale. If you take their details, thank them for the transaction and then find that the card is declined, you can phone them back and they are more likely to find another way of paying for the product. If the credit card is accepted you clear the details from the order. I cannot change this. The existing system stores the credit card details in clear text, and in the new system I am building to replace this I am clearly not going to replicate this! My question, then, is how I can securely store a credit card for a short period of time. I obviously want some kind of encryption, but what's the best way to do this? Environment: C#, WinForms, SQL-Server.

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  • Why do C compilers prepend underscores to external names?

    - by Michael Burr
    I've been working in C for so long that the fact that compilers typically add an underscore to the start of an extern is just understood... However, another SO question today got me wondering about the real reason why the underscore is added. A wikipedia article claims that a reason is: It was common practice for C compilers to prepend a leading underscore to all external scope program identifiers to avert clashes with contributions from runtime language support I think there's at least a kernel of truth to this, but also it seems to no really answer the question, since if the underscore is added to all externs it won't help much with preventing clashes. Does anyone have good information on the rationale for the leading underscore? Is the added underscore part of the reason that the Unix creat() system call doesn't end with an 'e'? I've heard that early linkers on some platforms had a limit of 6 characters for names. If that's the case, then prepending an underscore to external names would seem to be a downright crazy idea (now I only have 5 characters to play with...).

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  • are there any negative implications of sourcing a javascript file that does not actually exist?

    - by dreftymac
    If you do script src="/path/to/nonexistent/file.js" in an HTML file and call that in a browser, and there are no dependencies or resources anywhere else in the HTML file that expect the file or code therein to actually exist, is there anything inherently bad-practice about doing this? Yes, it is an odd question. The rationale is the developer is dealing with a CMS that allows custom (self-contained) javascript files to be provided in certain circumstances. The problem is the CMS is not very flexible when it comes to creating conditional includes for javascript. Therefore it is easier to just make references to the self-contained js files regardless of whether they are actually at the specified path. Since no errors are displayed to the user, should this practice be considered a viable option?

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  • Interface naming in Java

    - by Allain Lalonde
    Most OO languages prefix their interface names with a capital I, why does Java not do this? What was the rationale for not following this convention? To demonstrate what I mean, if I wanted to have a User interface and a User implementation I'd have two choices in Java: Class = User, Interface = UserInterface Class = UserImpl, Interface = User Where in most languages: Class = User, Interface = IUser Now, you might argue that you could always pick a most descriptive name for the user implementation and the problem goes away, but Java's pushing a POJO approach to things and most IOC containers use DynamicProxies extensively. These two things together mean that you'll have lots of interfaces with a single POJO implementation. So, I guess my question boils down to: "Is it worth following the broader Interface naming convention especially in light of where Java Frameworks seem to be heading?"

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