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• C++ & proper TDD

  - by Kotti

  Hi! I recently tried developing a small-sized project in C# and during the whole project our team used the Test-Driven-Development (TDD) technique (xunit, moq). I really think this was awesome, because (when paired with C#) this approach allowed to relax when coding, relax when projecting and relax when refactoring. I suspect that all this TDD-stuff actually simplifies the coding process and, well, it allowed (eventually, for me) to get the same result with fewer brain cells working. Right after that I tried using TDD paired with C++ (I used Google Test and Google Mock libraries), and, I don't know why but I actually think that TDD here was a step back in terms of rapid application development. I had some moments when I had to spend huge amounts of time thinking of my tests, building proper mocks, rebuilding them and swearing at my monitor. And, well, I obviously can't ask something like "what I did wrong?" or "what was wrong in my approach?", because I don't know what to describe. But if there are any people who are used to TDD in C++ (and, probably C#) too, could you please advise me how to do this properly. Framework recommendations, architecture approaches, plain coding advices - if you are experienced in TDD & C++, please respond.

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• Benefit of outputting JSON as opposed to plain HTML

  - by Franco

  Hey guys, Just wondering which is best here. I want to output data from a table in my DB then put a lot of this data into a html table on the fly on my page. Im working with Java on the server side. Basically I pull the results form the DB and have the raw data..just what next? There is a chance I may want to take data from multiple tables in order to combine it into one table for my site. I retrieve the results of the query from the DB, now do i create a text from it in the form of json which i can parse as json using jquery upon the return of the object to my browser?(kind of a sub question of this question: Is just using a stringbuilder the correct way to make a json object to output?) Or.. Should i build the HTML as a string and output that to the browser instead? Which is better and why? Thanks in advance!

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• Hashtable is that fast

  - by Costa

  Hi s[0]*31^(n-1) + s[1]*31^(n-2) + ... + s[n-1]. Is the hash function of the java string, I assume the rest of languages is similar or close to this implementation. If we have hash-Table and a list of 50 elements. each element is 7 chars ABCDEF1, ABCDEF2, ABCDEF3..... ABCDEFn If each bucket of hashtable contains 5 strings (I think this function will make it one string per bucket, but let us assume it is 5). If we call col.Contains("ABCDEFn"); // will do 6 comparisons and discover the difference on the 7th. The hash-table will take around 70 operations (multiplication and additions) to get the hashcode and to compare with 5 strings in bucket. and BANG it found. For list it will take around 300 comparisons to find it. for the case that there is only 10 elements, the list will take around 70 operations but the Hashtable will take around 50 operations. and note that hashtable operations are more time consuming (it is multiplications). I conclude that HybirdDictionary in .Net probably is the best choice for that most cases that require Hashtable with unknown size, because it will let me use a list till the list becomes more than 10 elements. still need something like HashSet rather than a Dictionary of keys and values, I wonder why there is no HybirdSet!! So what do u think? Thanks

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• Insert a Join Statement - (Insert Data to Multiple Tables) - C#/SQL/T-SQL/.NET

  - by peace

  I have a Winform that has fields need to be filled by a user. All the fields doesn't belong to one table, the data will go to Customer table and CustomerPhone table, so i decided to do multiple inserts. I will insert appropriate data to CustomerPhone first then Insert the rest data to Customer table. Is it possible to Join an Insert OR Insert a Join? If show me a rough sample, i will be grateful. Many Thanks

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• How do polymorphic inline caches work with mutable types?

  - by kingkilr

  A polymorphic inline cache works by caching the actual method by the type of the object, in order to avoid the expensive lookup procedures (usually a hashtable lookup). How does one handle the type comparison if the type objects are mutable (i.e. the method might be monkey patched into something different at run time). The one idea I've come up with would be a "class counter" that gets incremented each time a method is adjusted, however this seems like it would be exceptionally expensive in a heavily monkey patched environ since it would kill all the PICs for that class, even if the methods for them weren't altered. I'm sure there must be a good solution to this, as this issue is directly applicable to Javascript and AFAIK all 3 of the big JS VMs have PICs (wow acronym ahoy).

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• How can I detect 'any' ajax request being completed using jQuery?

  - by Brian Scott

  I have a page where I can insert some javascript / jquery to manipulate the output. I don't have any other control over the page markup etc. I need to add an extra element via jquery after each present on the page. The issue is that the elements are generated via an asynchronous call on the existing page which occurs after $(document).ready is complete. Essentially, I need a way of calling my jquery after the page has loaded and the subsequent ajax calls have completed. Is there a way to detect the completion of any ajax call on the page and then call my own custom function to insert the additional elements after the newly created s ?

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• RAII: Initializing data member in const method

  - by Thomas Matthews

  In RAII, resources are not initialized until they are accessed. However, many access methods are declared constant. I need to call a mutable (non-const) function to initialize a data member. Example: Loading from a data base struct MyClass { int get_value(void) const; private: void load_from_database(void); // Loads the data member from database. int m_value; }; int MyClass :: get_value(void) const { static bool value_initialized(false); if (!value_initialized) { // The compiler complains about this call because // the method is non-const and called from a const // method. load_from_database(); } return m_value; } My primitive solution is to declare the data member as mutable. I would rather not do this, because it suggests that other methods can change the member. How would I cast the load_from_database() statement to get rid of the compiler errors?

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• Is GAE Really GZipping My Content? Slow Response Times with GAE as CDN

  - by viatropos

  I am testing out Google App Engine as a free Content Delivery Network and it feels like it's taking a long time to serve up my content. Why does this gae page take a say a half a second to download, while your typical stack overflow page downloads much faster even with a ton more content? What am I missing here? All I have done is create an app and uploaded an image according to that tutorial, but content is being served very slowly it seems. Any suggestions? (Not considering Amazon or other CDNs right now, just looking for help with GAE). Note: I am using Safari when I visit those links, maybe safari is causing problems?

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• What limits scaling in this simple OpenMP program?

  - by Douglas B. Staple

  I'm trying to understand limits to parallelization on a 48-core system (4xAMD Opteron 6348, 2.8 Ghz, 12 cores per CPU). I wrote this tiny OpenMP code to test the speedup in what I thought would be the best possible situation (the task is embarrassingly parallel): // Compile with: gcc scaling.c -std=c99 -fopenmp -O3 #include <stdio.h> #include <stdint.h> int main(){ const uint64_t umin=1; const uint64_t umax=10000000000LL; double sum=0.; #pragma omp parallel for reduction(+:sum) for(uint64_t u=umin; u<umax; u++) sum+=1./u/u; printf("%e\n", sum); } I was surprised to find that the scaling is highly nonlinear. It takes about 2.9s for the code to run with 48 threads, 3.1s with 36 threads, 3.7s with 24 threads, 4.9s with 12 threads, and 57s for the code to run with 1 thread. Unfortunately I have to say that there is one process running on the computer using 100% of one core, so that might be affecting it. It's not my process, so I can't end it to test the difference, but somehow I doubt that's making the difference between a 19~20x speedup and the ideal 48x speedup. To make sure it wasn't an OpenMP issue, I ran two copies of the program at the same time with 24 threads each (one with umin=1, umax=5000000000, and the other with umin=5000000000, umax=10000000000). In that case both copies of the program finish after 2.9s, so it's exactly the same as running 48 threads with a single instance of the program. What's preventing linear scaling with this simple program?

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• Efficient way to delete a line from a text file (C#)

  - by Valentin Vasilyev

  Hello. I need to delete a certain line from a text file. What is the most efficient way of doing this? File can be potentially large(over million records). Thank you. UPDATE: below is the code I'm currently using, but I'm not sure if it is good. internal void DeleteMarkedEntries() { string tempPath=Path.GetTempFileName(); using (var reader = new StreamReader(logPath)) { using (var writer = new StreamWriter(File.OpenWrite(tempPath))) { int counter = 0; while (!reader.EndOfStream) { if (!_deletedLines.Contains(counter)) { writer.WriteLine(reader.ReadLine()); } ++counter; } } } if (File.Exists(tempPath)) { File.Delete(logPath); File.Move(tempPath, logPath); } }

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• Sharing [config] data across modules,functions

  - by williamstw

  I have some configuration data in a config file that I read off disk when the app starts. I need to make that configuration data available to other functions/modules in the application. I started down the path of looking into ets/mnesia to store the data on startup to make it shared among all processes, but then my inner voice cautioned me that there must be a more functional, erlang-y way to do this. The only alternate approach I've come up with so far is setting up a module that has an actor loop that reads the data on startup and responds to messages like {Key, From} and responds by From ! {ok,Value}. Then, I gave up and decided to ask... Thanks, --tim

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• Learn Fundamentals of Silverlight 4 Data Binding

  - by Eric J.

  I'm just starting to work with Silverlight (no WPF experience either) and am having a difficult time finding a source that provides a full explanation of Data Binding. There is absolutely no lack of tutorials (starting with the ones on Silverlight.net or Scott Gu's blogs), but everything I have found is "by example". Is there a resource that explains how data binding works in Silverlight, from a Fundamental/Conceptual perspective, and provides end-to-end coverage of data binding features? The desire for a more fundamental source of information is driven by a number of questions that came up this afternoon in reviewing tutorials and writing sample apps, such as: Why can't I bind the value of a slider like this?: Value="{Binding=Age, Mode=TwoWay}" where Age refers to an int property in the object data context I bind in code-behind (the Visual Studio error message is Expected '[]'. How do I use the DataContext property in VS 2010? What's a Path, Relative Source, Static Source, ...?

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• PostgreSQL: Why does this simple query not use the index?

  - by David

  I have a table t with a column c, which is an int and has a btree index on it. Why does the following query not utilize this index? explain select c from t group by c; The result I get is: HashAggregate (cost=1005817.55..1005817.71 rows=16 width=4) -> Seq Scan on t (cost=0.00..946059.84 rows=23903084 width=4) My understanding of indexes is limited, but I thought such queries were the purpose of indexes.

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• Why are difference lists more efficient than regular concatenation?

  - by Craig Innes

  I am currently working my way through the Learn you a haskell book online, and have come to a chapter where the author is explaining that some list concatenations can be ineffiecient: For example ((((a ++ b) ++ c) ++ d) ++ e) ++ f Is supposedly inefficient. The solution the author comes up with is to use 'difference lists' defined as newtype DiffList a = DiffList {getDiffList :: [a] -> [a] } instance Monoid (DiffList a) where mempty = DiffList (\xs -> [] ++ xs) (DiffList f) `mappend` (DiffList g) = DiffList (\xs -> f (g xs)) I am struggling to understand why DiffList is more computationally efficient than a simple concatenation in some cases. Could someone explain to me in simple terms why the above example is so inefficient, and in what way the DiffList solves this problem?

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• How do I make this nested for loop, testing sums of cubes, more efficient?

  - by Brian J. Fink

  I'm trying to iterate through all the combinations of pairs of positive long integers in Java and testing the sum of their cubes to discover if it's a Fibonacci number. I'm currently doing this by using the value of the outer loop variable as the inner loop's upper limit, with the effect being that the outer loop runs a little slower each time. Initially it appeared to run very quickly--I was up to 10 digits within minutes. But now after 2 full days of continuous execution, I'm only somewhere in the middle range of 15 digits. At this rate it may end up taking a whole year just to finish running this program. The code for the program is below: import java.lang.*; import java.math.*; public class FindFib { public static void main(String args[]) { long uLimit=9223372036854775807L; //long maximum value BigDecimal PHI=new BigDecimal(1D+Math.sqrt(5D)/2D); //Golden Ratio for(long a=1;a<=uLimit;a++) //Outer Loop, 1 to maximum for(long b=1;b<=a;b++) //Inner Loop, 1 to current outer { //Cube the numbers and add BigDecimal c=BigDecimal.valueOf(a).pow(3).add(BigDecimal.valueOf(b).pow(3)); System.out.print(c+" "); //Output result //Upper and lower limits of interval for Mobius test: [c*PHI-1/c,c*PHI+1/c] BigDecimal d=c.multiply(PHI).subtract(BigDecimal.ONE.divide(c,BigDecimal.ROUND_HALF_UP)), e=c.multiply(PHI).add(BigDecimal.ONE.divide(c,BigDecimal.ROUND_HALF_UP)); //Mobius test: if integer in interval (floor values unequal) Fibonacci number! if (d.toBigInteger().compareTo(e.toBigInteger())!=0) System.out.println(); //Line feed else System.out.print("\r"); //Carriage return instead } //Display final message System.out.println("\rDone. "); } } Now the use of BigDecimal and BigInteger was delibrate; I need them to get the necessary precision. Is there anything other than my variable types that I could change to gain better efficiency?

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• Multiple winform data save problem

  - by Mahesh

  hi am using C# with VS-2005 I have a form1 and about two textBox and one Combobox on it. like below textBox1 texbox2 ComboBox I have bind combobox by sql database. first user type in textbox1 and textbox2 and then goes to comboBox in which "BuyerName" available on it. if user not found the data in the comboBox then press ALT+C for opening of Form2 where they create data and save it. My problem is when I closed the form2 by saving data of "BuyerName" the form1 is open as per my requirement but the data of textBox1 and textBox2 which user typed before opening of form2 is lost and therefore user have to re-type on it. which i don't want as it wasting of time. I want when form2 closed and form1 open the data will be available on it. and when u create fresh "BuyerName" from form2 the "BuyerName" will be automaticaly available on form1 comboBox on closing of form2. Hope u will get it. am new here in programing so kindly suggest me by proper codeing. thx in Advance.

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• Tuning JVM (GC) for high responsive server application

  - by elgcom

  I am running an application server on Linux 64bit with 8 core CPUs and 6 GB memory. The server must be highly responsive. After some inspection I found that the application running on the server creates rather a huge amount of short-lived objects, and has only about 200~400 MB long-lived objects(as long as there is no memory leak) After reading http://java.sun.com/javase/technologies/hotspot/gc/gc_tuning_6.html I use these JVM options -Xms2g -Xmx2g -XX:MaxPermSize=256m -XX:NewRatio=1 -XX:+UseConcMarkSweepGC Result: the minor GC takes 0.01 ~ 0.02 sec, the major GC takes 1 ~ 3 sec the minor GC happens constantly. How can I further improve or tune the JVM? larger heap size? but will it take more time for GC? larger NewSize and MaxNewSize (for young generation)? other collector? parallel GC? is it a good idea to let major GC take place more often? and how?

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• How can I monitor the rendering time in a browser?

  - by adpd

  I work on an internal corporate system that has a web front-end as one of its interfaces. The web front-end is served up using Tomcat. How can I monitor the rendering time of specific pages in a browser (IE6)? I would like to be able to record the results in a log file (separate log file or the Tomcat access log).

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• [Ruby on Rails] Data Structure

  - by siulamvictor

  I am building a online form, with about 20 multiple choice checkboxes. I can get the nested data with this command. raise params.to_yaml I need to store these data and call them again later. I want to sort out which user chose which specific checkbox, i.e. who chose checkbox no.2? What's the best way to store these data in database?

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• receiving data from serialport stops when main form is minimized or moved

  - by Rahul

  Sir, I apologize if this is already covered somewhere. I did a search and find something which I have already implemented. I am developing an application which receives data from a device connected via serialport. I am using SerialPort datareceived event to capture data. I am to display data in text boxes of the main form. Data is received frequently. I used Timer to send command to the device, in response device send some data. Timer interval is 100 ms. In every 100 ms interval some command is sent and correspondingly data is received. I used Invoke function to update the GUI elements like TExtbox, labels etc. Everything is fine. All the elements are updating beautifully. But during receiving data if I make any change in main form like moving form, minimizing, maximizing, or clicking somewhere in the form, then data receiving stops. I couldnot find the reason why its happening ? I also changed the timer interval to 200,300,400,500 but same problem is there. Please tell me why its happening? And possible solution... Thanks In advance.... :)

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• how to merge ecommerce transaction data between two databases

  - by yamspog

  We currently run an ecommerce solution for a leisure and travel company. Everytime we have a release, we must bring the ecommerce site down as we update database schema and the data access code. We are using a custom built ORM where each data entity is responsible for their own CRUD operations. This is accomplished by dynamically generating the SQL based on attributes in the data entity. For example, the data entity for an address would be... [tableName="address"] public class address : dataEntity { [column="address1"] public string address1; [column="city"] public string city; } So, if we add a new column to the database, we must update the schema of the database and also update the data entity. As you can expect, the business people are not too happy about this outage as it puts a crimp in their cash-flow. The operations people are not happy as they have to deal with a high-pressure time when database and applications are upgraded. The programmers are upset as they are constantly getting in trouble for the legacy system that they inherited. Do any of you smart people out there have some suggestions?

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• Linq to SQL - what's better?

  - by msony

  db.Albums.FirstOrDefault(x => x.OrderId == orderId) or db.Albums.FirstOrDefault(x => x.OrderId.Equals(orderId))

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• Is there a module that implements an efficient array type in Erlang?

  - by dsmith

  I have been looking for an array type with the following characteristics in Erlang. append(vector(), term()) O(1) nth(Idx, vector()) O(1) set(Idx, vector(), term()) O(1) insert(Idx, vector(), term()) O(N) remove(Idx, vector()) O(N) I normally use a tuple for this purpose, but the performance characteristics are not what I would want for large N. My testing shows the following performance characteristics... erlang:append_element/2 O(N). erlang:setelement/3 O(N). I have started on a module based on the clojure.lang.PersistentVector implementation, but if it's already been done I won't reinvent the wheel.

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• WCF data service hosting in Windows Form

  - by user158598

  Hi, I want to host a WCF Data Service (formerly known as ADO.NET data Service) in windows form.Is it possible? If yes,then is there any blog, which talks about it? I know WCF can be hosted in Windows Form, but I am not sure about WCF data service, as all the examples I see, is asking to create ASP.NET web project. -Brajesh

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• Three level heirarchal data-linq

  - by user326010

  Hi I have three level heirarchal data. using the statement below i managed to display two level data. I need to extend it to one more level. Current heirachy is Modules--Documents I need to extend it as Packages--Modules--Documents var data = (from m in DataContext.SysModules join d in DataContext.SysDocuments on m.ModuleID equals d.ModuleID into tempDocs from SysDocument in tempDocs.DefaultIfEmpty() group SysDocument by m).ToList(); Regards Tassadaque

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