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  • What is the purpose of Java's unary plus operator?

    - by Syntactic
    Java's unary plus operator appears to have come over from C, via C++. As near as I can tell, it has the following effects: promotes its operand to int, if it's not already an int or wider unboxes its operand, if it's a wrapper object complicates slightly the parsing of evil expressions containing large numbers of consecutive plus signs It seems to me that there are better (or, at least, clearer) ways to do all of these things. In this SO question, concerning the counterpart operator in C#, someone said that "It's there to be overloaded if you feel the need." But in Java, one cannot overload any operator. So does this operator exist in Java just because it existed in C++?

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  • C: 8x8 -> 16 bit multiply precision guaranteed by integer promotions?

    - by craig-blome
    I'm trying to figure out if the C Standard (C90, though I'm working off Derek Jones' annotated C99 book) guarantees that I will not lose precision multiplying two unsigned 8-bit values and storing to a 16-bit result. An example statement is as follows: unsigned char foo; unsigned int foo_u16 = foo * 10; Our Keil 8051 compiler (v7.50 at present) will generate a MUL AB instruction which stores the MSB in the B register and the LSB in the accumulator. If I cast foo to a unsigned int first: unsigned int foo_u16 = (unsigned int)foo * 10; then the compiler correctly decides I want a unsigned int there and generates an expensive call to a 16x16 bit integer multiply routine. I would like to argue beyond reasonable doubt that this defensive measure is not necessary. As I read the integer promotions described in 6.3.1.1, the effect of the first line shall be as if foo and 10 were promoted to unsigned int, the multiplication performed, and the result stored as unsigned int in foo_u16. If the compiler knows an instruction that does 8x8-16 bit multiplications without loss of precision, so much the better; but the precision is guaranteed. Am I reading this correctly? Best regards, Craig Blome

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  • Code-Golf: Friendly Number Abbreviator

    - by David Murdoch
    Based on this question: Is there a way to round numbers into a friendly format? THE CHALLENGE - UPDATED! (removed hundreds abbreviation from spec) The shortest code by character count that will abbreviate an integer (no decimals). Code should include the full program. Relevant range is from 0 - 9,223,372,036,854,775,807 (the upper limit for signed 64 bit integer). The number of decimal places for abbreviation will be positive. You will not need to calculate the following: 920535 abbreviated -1 place (which would be something like 0.920535M). Numbers in the tens and hundreds place (0-999) should never be abbreviated (the abbreviation for the number 57 to 1+ decimal places is 5.7dk - it is unneccessary and not friendly). Remember to round half away from zero (23.5 gets rounded to 24). Banker's rounding is verboten. Here are the relevant number abbreviations: h = hundred (102) k = thousand (103) M = million (106) G = billion (109) T = trillion (1012) P = quadrillion (1015) E = quintillion (1018) SAMPLE INPUTS/OUTPUTS (inputs can be passed as separate arguments): First argument will be the integer to abbreviate. The second is the number of decimal places. 12 1 => 12 // tens and hundreds places are never rounded 1500 2 => 1.5k 1500 0 => 2k // look, ma! I round UP at .5 0 2 => 0 1234 0 => 1k 34567 2 => 34.57k 918395 1 => 918.4k 2134124 2 => 2.13M 47475782130 2 => 47.48G 9223372036854775807 3 => 9.223E // ect... . . . Original answer from related question (javascript, does not follow spec): function abbrNum(number, decPlaces) { // 2 decimal places => 100, 3 => 1000, etc decPlaces = Math.pow(10,decPlaces); // Enumerate number abbreviations var abbrev = [ "k", "m", "b", "t" ]; // Go through the array backwards, so we do the largest first for (var i=abbrev.length-1; i>=0; i--) { // Convert array index to "1000", "1000000", etc var size = Math.pow(10,(i+1)*3); // If the number is bigger or equal do the abbreviation if(size <= number) { // Here, we multiply by decPlaces, round, and then divide by decPlaces. // This gives us nice rounding to a particular decimal place. number = Math.round(number*decPlaces/size)/decPlaces; // Add the letter for the abbreviation number += abbrev[i]; // We are done... stop break; } } return number; }

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  • What features of interpreted languages can a compiled one not have?

    - by sub
    Interpreted languages are usually more high-level and therefore have features as dynamic typing (including creating new variables dynamically without declaration), the infamous eval and many many other features that make a programmer's life easier - but why can't compiled languages have these as well? I don't mean languages like Java that run on a VM, but those that compile to binary like C(++). I'm not going to make a list now but if you are going to ask which features I mean, please look into what PHP, Python, Ruby etc. have to offer. Which common features of interpreted languages can't/don't/do exist in compiled languages? Why?

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  • When is a good time to start thinking about scaling?

    - by Slokun
    I've been designing a site over the past couple days, and been doing some research into different aspects of scaling a site horizontally. If things go as planned, in a few months (years?) I know I'd need to worry about scaling the site up and out, since the resources it would end up consuming would be huge. So, this got me to thinking, when is the best time to start thinking about, and designing for, scalability? If you start too early on, you could easily over complicate your design, and make it impossible to actually build. You could also get too caught up in the details, the architecture, whatever, and wind up getting nothing done. Also, if you do get it working, but the site never takes off, you may have wasted a good chunk of extra effort. On the other hand, you could be saving yourself a ton of effort down the road. Designing it from the ground up to be big would make it much easier later on to let it grow big, with very little rewriting going on. I know for what I'm working on, I've decided to make at least a few choices now on the side of scaling, but I'm not going to do a complete change of thinking to get it to scale completely. Notably, I've redesigned my database from a conventional relational design to one similar to what was suggested on the Reddit site linked below, and I'm going to give memcache a try. So, the basic question, when is a good time to start thinking or worrying about scaling, and what are some good designs, tips, etc. for when doing so? A couple of things I've been reading, for those who are interested: http://www.codinghorror.com/blog/2009/06/scaling-up-vs-scaling-out-hidden-costs.html http://highscalability.com/blog/2010/5/17/7-lessons-learned-while-building-reddit-to-270-million-page.html http://developer.yahoo.com/performance/rules.html

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  • What are the lesser known but cool data structures ?

    - by f3lix
    There a some data structures around that are really cool but are unknown to most programmers. Which are they? Everybody knows linked lists, binary trees, and hashes, but what about Skip lists, Bloom filters for example. I would like to know more data structures that are not so common, but are worth knowing because they rely on great ideas and enrich a programmer's tool box. PS: I am also interested on techniques like Dancing links which make interesting use of the properties of a common data structure. EDIT: Please try to include links to pages describing the data structures in more detail. Also, try to add a couple of words on why a data structures is cool (as Jonas Kölker already pointed out). Also, try to provide one data-structure per answer. This will allow the better data structures to float to the top based on their votes alone.

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  • Does this data structure have a name? Sort of a "linked matrix"?

    - by Bob
    Let's say I wanted similar functionality to a doubly linked list but needed a matrix instead so that each node was structured like this: public class Node { Node Up, Down, Left, Right; object Value; } Is there a name for such a structure? I've looked through this Wikipedia listing of data structures but didn't see anything similar. Unless I just missed it.

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  • What does 'foo' really mean?

    - by Prakash
    I hope this qualifies as a programming question, as in any programming tutorial, you eventually come across 'foo' in the code examples. (yeah, right?) what does 'foo' really mean? If it is meant to mean nothing, when did it begin to be used so? Cheers

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  • C# internal VS VBNET Friend

    - by Will Marcouiller
    To this SO question: What is the C# equivalent of friend?, I would personally have answered "internal", just like Ja did among the answers! However, Jon Skeet says that there is no direct equivalence of VB Friend in C#. If Jon Skeet says so, I won't be the one telling otherwise! ;P I'm wondering how can the keyword internal (C#) not be the equivalent of Friend (VBNET) when their respective definitions are: Friend VBNET The Friend (Visual Basic) keyword in the declaration statement specifies that the elements can be accessed from within the same assembly, but not from outside the assembly. [...] internal C# Internal: Access is limited to the current assembly. To my understanding, these definitions mean quite the same to me. Then, respectively, when I'm coding in VB.NET, I use the Friend keyword to specify that a class or a property shall be accessible only within the assembly where it is declared. The same in C#, I use the internal keyword to specify the same. Am I doing something or anything wrong from this perspective? What are the refinements I don't get? Might someone please explain how or in what Friend and internal are not direct equivalences? Thanks in advance for any of your answers!

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  • C#: How to inherit constructors?

    - by Ian Boyd
    Imagine a base class with many constructors and a virtual method public class Foo { ... public Foo() {...} public Foo(int i) {...} ... public virtual void SomethingElse() {...} ... } and now I want to create a descendant class that overrides the virtual method: public class Bar : Foo { public override void SomethingElse() {...} } And another descendant that does some more stuff: public class Bah : Bar { public void DoMoreStuff() {...} } Do I really have to copy all constructors from Foo into Bar and Bah? And then if I change a constructor signature in Foo, do I have to update it in Bar and Bah? Is there no way to inherit constructors? Is there no way to encourage code reuse?

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  • A two way minimum spanning tree of a directed graph

    - by mvid
    Given a directed graph with weighted edges, what algorithm can be used to give a sub-graph that has minimum weight, but allows movement from any vertex to any other vertex in the graph (under the assumption that paths between any two vertices always exist). Does such an algorithm exist?

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  • Technical choices in unmarshaling hash-consed data

    - by Pascal Cuoq
    There seems to be quite a bit of folklore knowledge floating about in restricted circles about the pitfalls of hash-consing combined with marshaling-unmarshaling of data. I am looking for citable references to these tidbits. For instance, someone once pointed me to library aterm and mentioned that the authors had clearly thought about this and that the representation on disk was bottom-up (children of a node come before the node itself in the data stream). This is indeed the right way to do things when you need to re-share each node (with a possible identical node already in memory). This re-sharing pass needs to be done bottom-up, so the unmarshaling itself might as well be, too, so that it's possible to do everything in a single pass. I am in the process of describing difficulties encountered in our own context, and the solutions we found. I would appreciate any citable reference to the kind of aforementioned folklore knowledge. Some people obviously have encountered the problems before (the aterm library is only one example). But I didn't find anything in writing. Even the little piece of information I have about aterm is hear-say. I am not worried it's not reliable (you can't make this up), but "personal communication" and "look how it's done in the source code" are considered poor form in citations. I have enough references on hash-consing alone. I am only interested in references where it interferes with other aspects of programming, such as marshaling or distribution.

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  • What do we log and why do we log it?

    - by Lucas
    This has been bugging me for quite some time. Reading various questions on SO, blogs and listening to colleagues, I keep hearing how important "logging" is. How various logging frameworks stack up against each other, and how there are so many to pick from it's (apparently) ridiculous. Now, I know what logging is. What I don't know is what is supposed to be logged and why. Sure, I can guess. Exceptions? Sounds like something one might want to log... but which exceptions? And is it only exceptions? And what do I do with the logged information? If it's an in-house app, then that could probably be put to good use, but if it's a commercial desktop application, how is the log of... whatever... helping anyone? I doubt regular users would be peeking inside. Is it then something you ask the users to provide on request? I'm deeply frustrated by my own ignorance in this. It's also surprising how little information there is about this. The info on the websites of the various logging frameworks is all written for an audience that already knows what it wants to log, and knows why it needs to do so. Same things goes for the various discussions on SO about logging, like for instance this highly voted up question on Logging best practices. For a question with so many votes, it's almost comical how there's next to nothing in there that would answer my what and why questions. So being finally fed up, I'm asking here: what do people log, and why do they log it?

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  • Usage of closures with multiple arguments in swift

    - by Nilzone-
    This question is largely based on this one: Link The main difference being that I want to pass in arguments to the closure as well. Say I have something like this: func someFunctionThatTakesAClosure(completionClosure: (venues: Dictionary<String, AnyObject>, error: NSError) -> ()) { // function body goes here var error: NSError? let responseDictionary: Dictionary<String, AnyObject> = ["test" : "test2"] completionClosure(venues: responseDictionary, error: error!) } No error here. But when I call this function in my main view controller I have tried several ways but all of the result in different errors: venueService.someFunctionThatTakesAClosure(completionClosure(venues: Dictionary<String, AnyObject>, error: NSError){ }) or like this: venueService.someFunctionThatTakesAClosure((venues: Dictionary<String, AnyObject>, error: NSError){ }) or even like this: venueService.someFunctionThatTakesAClosure(completionClosure: (venues: Dictionary<String, AnyObject>, error: NSError) -> (){ }); I'm probably just way tired, but any help would be greatly appreciated!

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  • Is this a variation of the traveling salesman problem?

    - by Ville Koskinen
    I'm interested in a function of two word lists, which would return an order agnostic edit distance between them. That is, the arguments would be two lists of (let's say space delimited) words and return value would be the minimum sum of the edit (or Levenshtein) distances of the words in the lists. Distance between "cat rat bat" and "rat bat cat" would be 0. Distance between "cat rat bat" and "fat had bad" would be the same as distance between "rat bat cat" and "had fat bad", 4. In the case the number of words in the lists are not the same, the shorter list would be padded with 0-length words. My intuition (which hasn't been nurtured with computer science classes) does not find any other solution than to use brute force: |had|fat|bad| a solution ---+---+---+---+ +---+---+---+ cat| 2 | 1 | 2 | | | 1 | | ---+---+---+---+ +---+---+---+ rat| 2 | 1 | 2 | | 3 | | | ---+---+---+---+ +---+---+---+ bat| 2 | 1 | 1 | | | | 4 | ---+---+---+---+ +---+---+---+ Starting from the first row, pick a column and go to the next rows without ever revisiting a column you have already visited. Do this over and over again until you've tried all combinations. To me this sounds a bit like the traveling salesman problem. Is it, and how would you solve my particular problem?

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  • What features would you like to see added to C++?

    - by George Edison
    Are there any features you would like to see added to C++? Maybe... A programming construct An extra operator A built-in function you think would be useful I realize questions like this are frowned upon, but I think this one is a genuine programming question that can be answered and the answers will spawn valuable discussion. (And it's community wiki.) Here is one of mine: How come C++ has no exponent operator, like Python's **?

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  • Where do you start your design - code, UI, workflow or whatever?

    - by Mmarquee
    Hi I was discussing this at work, and was wondering where people start their designs? We tend to start with designing code to solve the problem presented to us, but that is probably all of us are (or were) programmers. I was wondering where other people and organisations start their design. Do they start with solving the problem as a coding problem, sit down and design what UI to use, or map out the data or workflow? Thanks

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  • The Definitive Guide To Website Authentication (beta)

    - by Michiel de Mare
    Form Based Authentication For Websites Please help us create the definitive resource for this topic. We believe that stackoverflow should not just be a resource for very specific technical questions, but also for general guidelines on how to solve variations on common problems. "Form Based Authentication For Websites" should be a fine topic for such an experiment. It should include topics such as: how to log in how to remain logged in how to store passwords using secret questions forgotten password functionality OpenID "Remember me" checkbox Browser autocompletion of usernames and passwords secret urls (public urls protected by digest) checking password strength email validation and much more It should not include things like: roles and authorization http basic authentication Please help us by Suggesting subtopics Submitting good articles about this subject Editing the official answer (as soon as you have enough karma) UPDATE: See the terrific 7-part series by Jens Roland below.

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  • Swift CMutablePointers in factories e.g. NewMusicSequence

    - by Gene De Lisa
    How do you use C level factory methods in Swift? Let's try using a factory such as NewMusicSequence(). OSStatus status var sequence:MusicSequence status=NewMusicSequence(&sequence) This errors out with "error: variable 'sequence' passed by reference before being initialized". Set sequence to nil, and you get EXC_BAD_INSTRUCTION. You can try being explicit like this: var sp:CMutablePointer<MusicSequence>=nil status=NewMusicSequence(sp) But then you get a bad access exception when you set sp to nil. If you don't set sp, you get an "error: variable 'sp' used before being initialized" Here's the reference.

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  • Semantically linking to code snippets

    - by Tim
    What's the most simple and semantic way of presenting code snippets in HTML? Possible XHTML syntax <a href="code_sample.php" type="text/x-php"> Example of widget creation </a> Example of linked file (code_sample.php): // Create a new widget $widget = new widget(); Pros: Semantically uses title to describe the source code being referenced Up to the client to render snippet Having very many custom server-side implementations tells me it should be standardized Browsers can have plug-ins for copy+paste, download, etc Seems to me this is where it belongs (not in Javascript) Degradation: non-compliant browsers receive a link to the associated content Cons: Not semantic enough? Seems wrong to replace hyperlinks with source code for presentation <object> might be better, but wouldn't degrade as nicely. Background I'm trying to create a "personal" XHTML standard for storing notes (wow, this is probably among the nerdiest things I've said). Since notes are just "scratch" it needs to be very lightweight. SO's markdown is very lightweight but not semantic enough for my needs. Plus, now I'm just curious. What's the most ideal syntax for linking to client-rendered code-snippets?

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