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• What are some good code optimization methods?

  - by esac

  I would like to understand good code optimization methods and methodology. How do I keep from doing premature optimization if I am thinking about performance already. How do I find the bottlenecks in my code? How do I make sure that over time my program does not become any slower? What are some common performance errors to avoid (e.g.; I know it is bad in some languages to return while inside the catch portion of a try{} catch{} block

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• How do I generate a random string of up to a certain length?

  - by slavy13

  I would like to generate a random string (or a series of random strings, repetitions allowed) of length between 1 and n characters from some (finite) alphabet. Each string should be equally likely (in other words, the strings should be uniformly distributed). The uniformity requirement means that an algorithm like this doesn't work: alphabet = "abcdefghijklmnopqrstuvwxyz" len = rand(1, n) s = "" for(i = 0; i < len; ++i) s = s + alphabet[rand(0, 25)] (pseudo code, rand(a, b) returns a integer between a and b, inclusively, each integer equally likely) It doesn't work because shorter lengths are as likely as longer ones, meaning it's more likely to generate a shorter string than a longer one, so the result is not uniform.

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• Determining when or when not to escape output

  - by Ygam

  I have a page, where I have approximately 90 items I need to output. Most of them are object properties (I am using ORM so these objects map to my database tables). But the question is, do I have to escape each of those 90 outputs by applying functions to each (in my case, the htmlspecialchars)? Wouldn't that add a bit of an overhead (calling a single function 90 times)?

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• How are a session identifiers generated?

  - by Asaf R

  Most web applications depend on some kind of session with the user (for instance, to retain login status). The session id is kept as a cookie in the user's browser and sent with every request. To make it hard to guess the next user's session these session-ids need to be sparse and somewhat random. The also have to be unique. The question is - how to efficiently generate session ids that are sparse and unique? This question has a good answer for unique random numbers, but it seems not scalable for a large range of numbers, simply because the array will end up taking a lot of memory.

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• How to handle printing of HTML pages?

  - by Jaran

  In my portfolio site I have listed my projects under separate tabs (tab menu). This works well except for printing which requires the user to click on a tab, print, click on the next tab and print the same page again to get everything. Being a portfolio I'd assume that visitors want to print all of the content. Is there a general way to create a different style when printing a web page? Or should I just add a printer icon on my page which redirects the user to a different page where all the data is in a big chunk and then prompt the user's browser to start printing?

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• Are there equivalents to Ruby's method_missing in other languages?

  - by Justin Ethier

  In Ruby, objects have a handy method called method_missing which allows one to handle method calls for methods that have not even been (explicitly) defined: Invoked by Ruby when obj is sent a message it cannot handle. symbol is the symbol for the method called, and args are any arguments that were passed to it. By default, the interpreter raises an error when this method is called. However, it is possible to override the method to provide more dynamic behavior. The example below creates a class Roman, which responds to methods with names consisting of roman numerals, returning the corresponding integer values. class Roman def romanToInt(str) # ... end def method_missing(methId) str = methId.id2name romanToInt(str) end end r = Roman.new r.iv #=> 4 r.xxiii #=> 23 r.mm #=> 2000 For example, Ruby on Rails uses this to allow calls to methods such as find_by_my_column_name. My question is, what other languages support an equivalent to method_missing, and how do you implement the equivalent in your code?

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• What GNU C extensions are available that aren't trivial to implement in C99?

  - by Yktula

  How come the Linux kernel can compile only with GCC? What GNU C extensions are really necessary for some projects and why?

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• What is a sensible maximum number of characters per line of code? [closed]

  - by Gudmundur Orn

  Everybody's screen size and font are different, so while my code fits on my screen, it might scroll off the right edge of your screen. What should be the maximum length of a line of code?

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• How strict should I be in the "do the simplest thing that could possible work" while doing TDD

  - by Support - multilanguage SO

  For TDD you have to Create a test that fail Do the simplest thing that could possible work to pass the test Add more variants of the test and repeat Refactor when a pattern emerge With this approach you're supposing to cover all the cases ( that comes to my mind at least) but I'm wonder if am I being too strict here and if it is possible to "think ahead" some scenarios instead of simple discover them. For instance, I'm processing a file and if it doesn't conform to a certain format I am to throw an InvalidFormatException So my first test was: @Test void testFormat(){ // empty doesn't do anything... processor.validate("empty.txt"); try { processor.validate("invalid.txt"); assert false: "Should have thrown InvalidFormatException"; } catch( InvalidFormatException ife ) { assert "Invalid format".equals( ife.getMessage() ); } } I run it and it fails because it doesn't throw an exception. So the next thing that comes to my mind is: "Do the simplest thing that could possible work", so I : public void validate( String fileName ) throws InvalidFormatException { if(fileName.equals("invalid.txt") { throw new InvalidFormatException("Invalid format"); } } Doh!! ( although the real code is a bit more complicated, I found my self doing something like this several times ) I know that I have to eventually add another file name and other test that would make this approach impractical and that would force me to refactor to something that makes sense ( which if I understood correctly is the point of TDD, to discover the patterns the usage unveils ) but: Q: am I taking too literal the "Do the simplest thing..." stuff?

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• If you use MVC in your web app then you dont need to use Smarty(TemplateEngine) Right?

  - by Imran

  I'm just trying to understand the Templating(system). If you use MVC in your web application then you don't need to use something like Smarty(template engine) as you are already separating application code from presentation code anyway by using MVC right? please correct me? So am i correct in thinking it's MVC OR Templating or do you use both in your apps?If any one could explain this in detail it would be great. Thank you in advance;-)

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• Testing When Correctness is Poorly Defined?

  - by dsimcha

  I generally try to use unit tests for any code that has easily defined correct behavior given some reasonably small, well-defined set of inputs. This works quite well for catching bugs, and I do it all the time in my personal library of generic functions. However, a lot of the code I write is data mining code that basically looks for significant patterns in large datasets. Correct behavior in this case is often not well defined and depends on a lot of different inputs in ways that are not easy for a human to predict (i.e. the math can't reasonably be done by hand, which is why I'm using a computer to solve the problem in the first place). These inputs can be very complex, to the point where coming up with a reasonable test case is near impossible. Identifying the edge cases that are worth testing is extremely difficult. Sometimes the algorithm isn't even deterministic. Usually, I do the best I can by using asserts for sanity checks and creating a small toy test case with a known pattern and informally seeing if the answer at least "looks reasonable", without it necessarily being objectively correct. Is there any better way to test these kinds of cases?

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• Sort months ( with strings ) algorithm

  - by Oscar Reyes

  I have this months array: ["January", "March", "December" , "October" ] And I want to have it sorted like this: ["January", "March", "October", "December" ] I'm currently thinking in a "if/else" horrible cascade but I wonder if there is some other way to do this. The bad part is that I need to do this only with "string" ( that is, without using Date object or anything like that ) What would be a good approach?

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• What's the purpose of the empty string?

  - by Max Toro

  To me, as a developer and as a user, I find the empty string ("") useless and the cause of much confusion, it's like saying string == char[] Maybe computers need the empty string, so I'd like to learn why.

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• What is an efficient way to find a non-colliding rectangle nearest to a location

  - by hyn

  For a 2D game I am working on, I am using y axis sorting in a simple rectangle-based collision detection. This is working fine, and now I want to find the nearest empty rectangle at a given location with a given size, efficiently. How can I do this? Is there an algorithm? I could think of a simple brute force grid test (with each grid the size of the empty space we're looking for) but obviously this is slow and not even a complete test.

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• Parsing: How to make error recovery in grammars like " a* b*"?

  - by Lavir the Whiolet

  Let we have a grammar like this: Program ::= a* b* where "*" is considered to be greedy. I usually implement "*" operator naively: Try to apply the expression under "*" to input one more time. If it has been applied successfully then we are still under current "*"-expression; try to apply the expression under "*" one more time. Otherwise we have reached next grammar expression; put characters parsed by expression under "*" back into input and proceed with next expression. But if there are errors in input in any of "a*" or "b*" part such a parser will "think" that in position of error both "a*" and "b*" have finished ("let's try "a"... Fail! OK, it looks like we have to proceed to "b*". Let's try "b"... Fail! OK, it looks like the string should have been finished...). For example, for string "daaaabbbbbbc" it will "say": "The string must end at position 1, delete superflous characters: daaaabbbbbbc". In short, greedy "*" operator becomes lazy if there are errors in input. How to make "*" operator to recover from errors nicely?

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• Tree-like queues

  - by Rehno Lindeque

  I'm implementing a interpreter-like project for which I need a strange little scheduling queue. Since I'd like to try and avoid wheel-reinvention I was hoping someone could give me references to a similar structure or existing work. I know I can simply instantiate multiple queues as I go along, I'm just looking for some perspective by other people who might have better ideas than me ;) I envision that it might work something like this: The structure is a tree with a single root. You get a kind of "insert_iterator" to the root and then push elements onto it (e.g. a and b in the example below). However, at any point you can also split the iterator into multiple iterators, effectively creating branches. The branches cannot merge into a single queue again, but you can start popping elements from the front of the queue (again, using a kind of "visitor_iterator") until empty branches can be discarded (at your discretion). x -> y -> z a -> b -> { g -> h -> i -> j } f -> b Any ideas? Seems like a relatively simple structure to implement myself using a pool of circular buffers but I'm following the "think first, code later" strategy :) Thanks

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• What is a typical algorithm for finding a string within a string?

  - by Courtney85

  I recently had an interview question that went something like this: Given a large string (haystack), find a substring (needle)? I was a little stumped to come up with a decent solution. What is the best way to approach this that doesn't have a poor time complexity?

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• Fast, Vectorizable method of taking floating point number modulus of special primes?

  - by caffiend

  Is there a fast method for taking the modulus of a floating point number? With integers, there are tricks for Mersenne primes, so that its possible to calculate y = x MOD 2^31 without needing division. Can any similar tricks be applied for floating point numbers? Preferably, in a way that can be converted into vector/SIMD operations, or moved into GPGPU code. The primes I'm interested in would be 2^7 and 2^31, although if there are more efficient ones for floating point numbers, those would be welcome.

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• Is there a website to lookup already common code functions?

  - by pinnacler

  I'm sitting here writing a function that I'm positive has been written before, somewhere on earth. It's just too common to have not been attempted, and I'm wondering why I can't just go to a website and search for a function that I can then copy and paste into my project in 2 seconds, instead of wasting my day reinventing the wheel. Sure there are certain libraries you can use, but where do you find these libraries and when they are absent, is there a site like I'm describing?

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• Randomly sorting an array

  - by Cam

  Does there exist an algorithm which, given an ordered list of symbols {a1, a2, a3, ..., ak}, produces in O(n) time a new list of the same symbols in a random order without bias? "Without bias" means the probability that any symbol s will end up in some position p in the list is 1/k. Assume it is possible to generate a non-biased integer from 1-k inclusive in O(1) time. Also assume that O(1) element access/mutation is possible, and that it is possible to create a new list of size k in O(k) time. In particular, I would be interested in a 'generative' algorithm. That is, I would be interested in an algorithm that has O(1) initial overhead, and then produces a new element for each slot in the list, taking O(1) time per slot. If no solution exists to the problem as described, I would still like to know about solutions that do not meet my constraints in one or more of the following ways (and/or in other ways if necessary): the time complexity is worse than O(n). the algorithm is biased with regards to the final positions of the symbols. the algorithm is not generative. I should add that this problem appears to be the same as the problem of randomly sorting the integers from 1-k, since we can sort the list of integers from 1-k and then for each integer i in the new list, we can produce the symbol ai.

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• Problem Naming an Interface

  - by Jens Schauder

  I have an interface named PropertyFilter which used to take a Propertyand decide if accepts it or not. And the world was good. But now the interface changed, so that implementations may choose to add additional Propertys. For example a Customer property might get expanded into Name and Address properties. I think it is obvious this is not a Filter anymore, but how would you call such a thing?

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• How to declare class attributes in swift, just like UITableViewCell reuse identifiers?

  - by martin

  I am trying to declare a reuse identifier associated to a UITableView subclass in swift. From my understanding I would like to declare an class stored property (not an instance one) so i have access via: MyCustomTableCell.ReuseIdentifer. Here is what I was trying: class MyCustomTableViewCell : UITableViewCell { class let ReuseIdentifier = "MyCustomTableViewCellReuseIdentifier" } The compiler mentions that class attributes are not supported yet. How to declare such kind of constants associated to a class type in a clean way?

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• Why is forwarding variadic parameters invalid?

  - by awesomeyi

  Consider the variadic function parameter: func foo(bar:Int...) -> () { } Here foo can accept multiple arguments, eg foo(5,4). I am curious about the type of Int... and its supported operations. For example, why is this invalid? func foo2(bar2:Int...) -> () { foo(bar2); } Gives a error: Could not find an overload for '_conversion' that accepts the supplied arguments Why is forwarding variadic parameters invalid? What is the "conversion" the compiler is complaining about?

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• What different terms mean the same thing (or don't, but people think they do)?

  - by Matthew Jones

  One of the pitfalls I run into on a daily basis is customers saying one thing while meaning another. Usually, this is just due to a miscommunication somewhere, but occasionally they are, in fact, saying the same thing I am just using a different term. For example, one of my customers the other day mentioned a feature he called, "find as you type." Being a little confused, I asked him what he meant, and he described the feature in Google where, once you start typing a search query, Google suggests other, popular queries that match the letters you have typed. Click! He meant AutoComplete! He was not wrong, it is just that I had never heard that term before. In the spirit of reducing confusion, what terms can you think of that are different but mean, essentially, the same thing? Also, what terms do people think mean the same thing, but don't. Please differentiate between the two. Please only one set of terms per answer, so we can vote on the best ones.

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• Starting a code library.

  - by Rob Stevenson-Leggett

  Hi, I've been meaning to start a library of reusable code snippets for a while and never seem to get round to it. I think my main problems are: Where to start. What structure should my library take? Should it be a compiled library (where appropriate or just classes I can drop into any project? Or a library project that can be included? In my experience, a built library will quickly become out of date and the source will get lost. So I'm leaning towards source libraries that I can export from SVN and include in any project. Intellectual property. I am employeed, so a lot of the code I write is not my IP. How can I ensure that I don't give my own IP away using it on projects in work and at home? I'm thinking the best way would be to licence my library with an open source licence and make sure I only add to it in my own time using my own equipment and therefore making sure that if I use it in a work project the same rules apply as if I was using a third party library. I write in many different languages and often would require two or more parts of this library. Should I look at implementing a few template projects and a core project for each of my chosen reusable components and languages? Has anyone else got this sort of library and how do you organise and update it?

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