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• C#. Struct design. Why 16 byte is recommended size?

  - by maxima120

  I read Cwalina book (recommendations on development and design of .NET apps). He says that good designed struct has to be less than 16 bytes in size (for performance purpose). My questions is - why exactly is this? And (more important) can I have larger struct with same efficiency if I run my .NET 3.5 (soon to be .NET 4.0) 64-bit application on i7 under Win7 x64 (is this limitation CPU / OS based)? Just to stress again - I need as efficient struct as it is possible. I try to keep it in stack all the time, the application is heavily multi-threaded and runs on sub-millisecond intervals, the current size of the struct is 64 byte.

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• Oracle spatial search within distance

  - by KA_lin

  I have the following table Cities: ID(int),City(char),latitude(float),longitude(float). Now based on a user`s longitude(ex:44.8) and latitude(ex:46.3) I want to search for all the cities near him within 100 miles/KM. I have found some examples but don`t know how to adapt them to my case select * from GEO.Cities a where SDO_WITHIN_DISTANCE([I don`t know], MDSYS.SDO_GEOMETRY(2001, 8307, MDSYS.SDO_POINT_TYPE(44.8,46.3, NULL) ,NULL, NULL), 'distance = 1000') = 'TRUE'; Any help would be appreciated. P.S: If it is possible to have the distance and to be sorted P.P.S: I want to do it in this way due to performance issues, I have done this in this way http://www.scribd.com/doc/2569355/Geo-Distance-Search-with-MySQL but it takes too long...

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• Attention all SQL gods! Query help needed.

  - by gurun8

  I need a little help putting together a SQL query that will give me the following resultsets: and The data model looks like this: The tricky part for me is that the columns to the right of the "Product" in the resultset are really columns in the database but rather key/value pairs spanned across the data model. Table data is as follows: My apologies in advance for the image heavy question and the image quality. This just seemed like the easiest way to convey the information. It'll probably take someone less time to write the query statement to achieve the results. By the way, the "product_option" table image is truncated but it illustrated the general idea of the data structure. The MySQL server version is 5.1.45.

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• Unrecognized option: -o Could not create the Java virtual machine.

  - by Kerubu

  I've got an unusual build error when using Buildroot to create an image for my Phidget SBC. It's unusual because it occurs ONLY on my development laptop and NOT on my general use laptop even though I am using EXACTLY the same Builroot environment as published by Phidgets themselves. When I try to create my Buildroot image I get the following error when it attempts to compile GNU classpath: Making all in tools make[2]: Entering directory `/home/xxxx/buildroot_phidgetsbc/buildroot-phidgetsbc_1.0.4.20111028/output/build/classpath-0.98/tools' /bin/mkdir -p classes asm /bin/mkdir -p ../tools/generated/gnu/classpath/tools/gjdoc/expr java -classpath antlr.Tool -o ../tools/generated/gnu/classpath/tools/gjdoc/expr/ \ ./gnu/classpath/tools/gjdoc/expr/java-expression.g Unrecognized option: -o Could not create the Java virtual machine. make[2]: *** [tools.zip] Error 1 The only difference I can possibly thing of is the different Linux (Ubuntu) versions I am using on each laptop. Also I cannot find a -o option documented for Java and don't understand why it works on one laptop but not the other. Any suggestions would be helpful.

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• Which are the current/emerging desktop development technologies worth looking into?

  - by heeboir

  Greetings, With all the existing development towards web development and emerging technologies in that area, I'm left wondering; what is a state of the art way to implement desktop applications in this day and age? If you were to start a new application of considerable size from scratch what technology would you invest your efforts in (focusing on cross platform portability, decent performance and interoperability with existing standards)? I've looked into the Adobe Air platform which appears quite impressive but seems rather limited to support a large application. Would something like Java/SWT still be the sensible choice? Do things like GWT fit the bill? Thanks P.S. I'm leaving my question a bit open-ended in an effort to gather diverse answers. Surely this a subjective matter and there is no right and wrong answer.

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• How to pass a reference to a string in JavaScript?

  - by ijjo

  Maybe a closure is my solution? Not exactly sure how to pull it off though. The code is set up like so: var globalVar = ''; var globalVar2 = ''; function func() { if (condition) func2(globalVar) else func2(globalVar2) } In func2() I cache some HTML in a main container into the appropriate global variable that I pass to it. Basically I have a main container that holds different pages depending on what tab they choose. For performance I want to cache the page into global vars so I need to know what tab is active to figure out which global var to assign the HTML to.

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• Proper programming procedure?

  - by Rob

  I am creating a scoring application which is dependent upon what a user selects at the beginning menu. Example: If a user clicks 18, I want it to base itself off 18 holes of golf. If a user clicks 9, I want it to base itself off 9 holes of golf. Is it better to create a separate class for the code for 9 holes, and then another for 18 holes and then launch whichever depending on what the user selects? Or should I keep everything in 1 file and use a global variable to define different parameters? Still very new to android programming (or programming in general) so not sure of the proper "etiquette" if you will... Also what would be the pro's and con's of doing it either way? (If any) Thanks in advance!

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• Question About Eclipse Java Debugger Conditional Breakpoints Inefficiency

  - by Personman

  I just set a conditional breakpoint in Eclipse's debugger with a mildly inefficient condition by breakpoint standards - checking whether a HashMap's value list (8 elements) contains Double.NaN. This resulted in an extremely noticeable slowdown in performance - after about five minutes, I gave up. Then I copy pasted the condition into an if statement at the exact same line, put a noop in the if, and set a normal breakpoint there. That breakpoint was reached in the expected 20-30 seconds. Is there something special that conditional breakpoints do that is different from this, or is Eclipse's implementation just kinda stupid? It seems like they could fairly easily just do exactly the same thing behind the scenes.

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• Design guidelines for cache mechanism

  - by Delashmate

  Hi All, I got assignment to write design for cache mechanism (this is work assignment, not homework), This is my first time writing a design document, Our program display images for doctors, and we want to reduce the parsing time of the images So we want to save the parsed data in advance (in files or inside database) Currently I have several design key ideas: Handle locks - each shared data structure should be handled, also files Test - add test to verify the data from the cache is equal to the data from the files To decouple the connection to the database- not to call directly to the database Cleanup mechanisem- to delete old files if the cahce directory exceed configurable threshold Support config file Support performance tool in the feature I will also add class diagram, data flow charts, and workflow What do you think I should add to the key ideas? Do you know good link to atricales about design? Thanks in advance, Dan

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• Can Silverlight be linked with a C++ static library ?

  - by Niklaos

  Hi, I'm currently doing research to start a new project. This project will be in 2 parts a light Client (probably console) and an heavy one using silverlight. The light client must be cross-platform. However, they will both use the same Core (by the way, the core will need to use the sockets). I'd like to use C++ to build the light client but given that the core is common to both applications, it would be much appreciated if it's could be the same code. So the question is quite simple : Can Silverlight be compilated with a C++ static library ? And if it's possible, what about cross-platform issues (with moonlight) ? If it's not possible. Which language can i use to work with silverlight while being cross-platform ? Because of performance, a compilated language will be better ! Thanks for your expertise :)

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• DB management for Heroku apps

  - by zetarun

  Hi all, I'm fairly new to both Rails and Heroku but I'm seriously thinking of using it as a platform to deploy my Ruby/Rails applications. I want to use all the power of Heroku, so I prefer the "embedded" PostgreSQL managed by Heroku instead of the addon for Amazon RDS for MySQL, but I'm not so confident without the possibility to access my data in a SQL client... I know that in a well made app you have no need to access DB, but there are some situations (add rows to a config table, see data not mapped in a view, update some columns for debugging issues, performance monitoring, running queries for reporting, etc.) when this can be good... How do you solve this problem? What's you experience in a real life app powered by Heroku? Thanks!

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• Is there a way to ignore Cache errors in Django?

  - by Josh Smeaton

  I've just set our development Django site to use redis for a cache backend and it was all working fine. I brought down redis to see what would happen, and sure enough Django 404's due to cache backend behaviour. Either the Connection was refused, or various other errors. Is there any way to instruct Django to ignore Cache errors, and continue processing the normal way? It seems weird that caching is a performance optimization, but can bring down an entire site if it fails. I tried to write a wrapper around the backend like so: class CacheClass(redis_backend.CacheClass): """ Wraps the desired Cache, and falls back to global_settings default on init failure """ def __init__(self, server, params): try: super(CacheClass, self).__init__(server, params) except Exception: from django.core import cache as _ _.cache = _.get_cache('locmem://') But that won't work, since I'm trying to set the cache type in the call that sets the cache type. It's all a very big mess. So, is there any easy way to swallow cache errors? Or to set the default cache backend on failure?

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• Why is 'using namespace std;' considered a bad practice in C++?

  - by Mana

  Okay, sorry for the simplistic question, but this has been bugging me ever since I finished high school C++ last year. I've been told by others on numerous occasions that my teacher was wrong in saying that we should have "using namespace std;" in our programs, and that std::cout and std::cin are more proper. However, they would always be vague as to why this is a bad practice. So, I'm asking now: Why is "using namespace std;" considered bad? Is it really that inefficient, or risk declaring ambiguous vars(variables that share the same name as a function in std namespace) that much? Or does this impact program performance noticeably as you get into writing larger applications? I'm sorry if this is something I should have googled to solve; I figured it would be nice to have this question on here regardless in case anyone else was wondering.

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• find lowest neighbor matlab

  - by user1812719

  I am trying to write a function [offset,coffset]=findLowNhbr(map) that for each pixel in a map finds the eight neighbors to the pixel, and returns two matrices with both the row and column offsets to the lowest neighbor (uses the numbers -1, 0 and 1). Border pixels are given 0 offsets for both the row and column, since they do not have neighbors. Here is what I think the general plan for this function should be: For each point, find the eight nearest neighbors. If the neighbor is lower than the point, return -1 If the neighbor is at the same elevation as the point, return 0 If the neighbor is higher than the point, return +1 Store these offsets in two matrices. I am at a complete loss as to where to start, so any advice or questions are welcome!

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• Click Listener not invoked within ListFragment

  - by membersound

  I'm extending a SherlockListFragment, but it should not matter as my question seems to be more general related to Fragments. Now, I implement a simple click listener for my list, but it does not get called. public class MyListFragment extends SherlockListFragment { @Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { View v = inflater.inflate(R.layout.list, container, false); v.setOnClickListener(new OnClickListener() { public void onClick(View view) { Log.i("debug", "single click"); } }); return v; } } Is anything wrong with this? //Solution: listView.setOnItemClickListener(new OnItemClickListener() { @Override public void onItemClick(AdapterView<?> parent, View view, int position, long id) { Log.i("debug", "single click"); } });

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• Who owes who money optimisation problem

  - by Francis

  Say you have n people, each who owe each other money. In general it should be possible to reduce the amount of transactions that need to take place. i.e. if X owes Y £4 and Y owes X £8, then Y only needs to pay X £4 (1 transaction instead of 2). This becomes harder when X owes Y, but Y owes Z who owes X as well. I can see that you can easily calculate one particular cycle. It helps for me when I think of it as a fully connected graph, with the nodes being the amount each person owes. Problem seems to be NP-complete, but what kind of optimisation algorithm could I make, nevertheless, to reduce the total amount of transactions? Doesn't have to be that efficient, as N is quite small for me.

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• How can I add floats together in different orders, and always get the same total?

  - by splicer

  Let's say I have three 32-bit floating point values, a, b, and c, such that (a + b) + c != a + (b + c). Is there summation algorithm, perhaps similar to Kahan summation, that guarantees that these values can be summed in any order and always arrive at the exact same (fairly accurate) total? I'm looking for the general case (i.e. not a solution that only deals with 3 numbers). Is arbitrary precision arithmetic the only way to go? I'm dealing with very large data sets, so I'd like to avoid the overhead of using arbitrary precision arithmetic if possible. Thanks!

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• Why is this loop over mysql resultset slow? (1.4ms per cycle)

  - by pawpro

  The $res contains around 488k rows the whole loop takes 61s! that's over 1.25ms per cycle! What is taking all that time? while($row = $res->fetch_assoc()) { $clist[$row['upload_id']][$row['dialcode_id']][$row['carrier_id']]['std'] = $row['cost_std']; $clist[$row['upload_id']][$row['dialcode_id']][$row['carrier_id']]['ecn'] = $row['cost_ecn']; $clist[$row['upload_id']][$row['dialcode_id']][$row['carrier_id']]['wnd'] = $row['cost_wnd']; $dialcode_destination[$row['upload_id']][$row['carrier_id']][$row['dialcode_id']]['other_destination'] = $row['destination_id']; $dialcode_destination[$row['upload_id']][$row['carrier_id']][$row['dialcode_id']]['carrier_destination'] = $row['carrier_destination_id']; } Now resultset of 10 rows, smaller arrays and performance 30 times higher (0.041ms) not the fastest still but better. while($row = $res->fetch_assoc()) { $customer[$row['id']]['name'] = $row['name']; $customer[$row['id']]['code'] = $row['customer']; }

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• Using function arguments as local variables

  - by Rubys

  Something like this (yes, this doesn't deal with some edge cases - that's not the point): int CountDigits(int num) { int count = 1; while (num >= 10) { count++; num /= 10; } return count; } What's your opinion about this? That is, using function arguments as local variables. Both are placed on the stack, and pretty much identical performance wise, I'm wondering about the best-practices aspects of this. I feel like an idiot when I add an additional and quite redundant line to that function consisting of int numCopy = num, however it does bug me. What do you think? Should this be avoided?

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• How to prevent CAST errors on SSIS ?

  - by manitra

  Hello, The question Is it possible to ask SSIS to cast a value and return NULL in case the cast is not allowed instead of throwing an error ? My environment I'm using Visual Studio 2005 and Sql Server 2005 on Windows Server 2003. The general context Just in case you're curious, here is my use case. I have to store data coming from somewhere in a generic table (key/value structure with history) witch contains some sort of value that can be strings, numbers or dates. The structure is something like this : table Values { Id int, Date datetime, -- for history Key nvarchar(50) not null, Value nvarchar(50), DateValue datetime, NumberValue numeric(19,9) } I want to put the raw value in the Value column and try to put the same value in the DateValue column when i'm able to cast it to Datetime in the NumberValue column when i'm able to cast it to a number Those two typed columns would make all sort of aggregation and manipulation much easier and faster later. That's it, now you know why i'm asking this strange question. ============ Thanks in advance for your help.

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• Using pthread condition variable with rwlock

  - by Doomsday

  Hello, I'm looking for a way to use pthread rwlock structure with conditions routines in C++. I have two questions: First: How is it possible and if we can't, why ? Second: Why current POSIX pthread have not implemented this behaviour ? To understand my purpose, I explain what will be my use: I've a producer-consumer model dealing with one shared array. The consumer will cond_wait when the array is empty, but rdlock when reading some elems. The producer will wrlock when adding(+signal) or removing elems from the array. The benefit of using rdlock instead of mutex_lock is to improve performance: when using mutex_lock, several readers would block, whereas using rdlock several readers would not block.

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• Help With Prolog Lists

  - by BeginnerPro

  Hi, Im new to Prolog and was looking for some assistance. What i am trying to do is basically get the some of the list of list, if that makes sense? lol What i am trying to achieve is.... sum([ [1,2],[3,4],[5,6] ]). should return: Number Of Lists: 3 List 1 3 List 2 7 List 3 11....etc I can get the Number of Lists which is fairly simple but im not quite sure how to loop through the List and then for each List add the number up. Am i making this more complicated than it actually is? lol! If anyone can help me or point me in the general direction that would be great. Thanks in advance

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• NSCurrentLocaleDidChangeNotification on iPhone OS

  - by 0xced

  While the NSCurrentLocaleDidChangeNotification perfectly makes sense on Mac OS X, I don't see how you can possibly receive it on iPhone OS. In order to change the locale, you have to quit the running application, then change it in Settings ? General ? International ? Region Format. At that point, your app is not running, so how could it receive the notification? I first thought this notification was leftover from the Mac OS X documentation, but then I found this in Apple Push Notification Service Programming Guide: The application might send its provider the preferred language every time the user changes something in the current locale. To do this, you can listen for the notification named NSCurrentLocaleDidChangeNotification and, in your notification-handling method, get the code identifying the preferred language and send that to your provider. So, how do you trigger this notification on iPhone OS?

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• Any dynamic database frontend tool from which you can update directly?

  - by Enjoy coding

  Hi Gurus, This is with reference to this question where I got one tabular report format. I need to update the user entered values correctly back to the same table rows. I am in the process of doing this by using general form post data methods by using some logics which I think will not be easy to maintain. So, just out of curiosity, Is there a front end creator javascript libraries or frameworks which can create the front end for any query's resultset and updates the corresponding rows when the user updates them from front end. This need not have all the full functionality, any one usable, customizable thing will reduce the code maintenance problems. I have googled for some javascript libraris for this but not able to get which will be suitable. Please suggest any useful tools. My environment is Mysql, PHP, JQuery, XAMPP server on Windows. Is JQuery provides one. Thanks in advance.

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• Separating merged array of arithmetic and geometric series

  - by user1814037

  My friend asked me an interseting question. Given an array of positive integers in increasing order. Seperate them in two series, an arithmetic sequence and geometric sequence. The given array is such that a solution do exist. The union of numbers of the two sequence must be the given array. Both series can have common elements i.e. series need not to be disjoint. The ratio of the geometric series can be fractional. Example: Given series : 2,4,6,8,10,12,25 AP: 2,4,6,8,10,12 GP: 4,10,25 I tried taking few examples but could not reach a general way. Even tried some graph implementation by introducing edges if they follow a particular sequence but could not reach solution.

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