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• Whats the best data-structure for storing 2-tuple (a, b) which support adding, deleting tuples and c

  - by bhups

  Hi So here is my problem. I want to store 2-tuple (key, val) and want to perform following operations: - keys are strings and values are Integers - multiple keys can have same value - adding new tuples - updating any key with new value (any new value or updated value is greater than the previous one, like timestamps) - fetching all the keys with values less than or greater than given value - deleting tuples. Hash seems to be the obvious choice for updating the key's value but then lookups via values will be going to take longer (O(n)). The other option is balanced binary search tree with key and value switched. So now lookups via values will be fast (O(lg(n))) but updating a key will take (O(n)). So is there any data-structure which can be used to address these issues? Thanks.

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• Is there any framework for Windows Forms, DB driven application development/prototyping?

  - by dolzenko

  I'm writing simple database driven application, 80% of functionality is CRUD operations on about 15 tables. Coming from web development background I figured I can cover almost all of these CRUD cases with Rails scaffolding or say Django admins. So I started to look around for Rails/Django-like framework but for Windows Forms applications (ofcourse I understand that "rich client" application development significantly differs from a web development and I'm not expecting anything really similar). I was surprised that except for a variety of ORMs (let's call it Model-layer) it seems like I'm left with little choice when it comes to View-Controller layer. Maybe I'm missing something? PS. I evaluated Visual Studio DataSet Designer, but it seems to work only for the most simple cases, and requires additional code for any slightly nontrivial task. (added) so far I've found: TrueView for .NET (thanks to Vijay Patel) NConstruct

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• Why do C++ streams use char instead of unsigned char?

  - by Johannes Schaub - litb

  I've always wondered why the C++ Standard library has instantiated basic_[io]stream and all its variants using the char type instead of the unsigned char type. char means (depending on whether it is signed or not) you can have overflow and underflow for operations like get(), which will lead to implementation-defined value of the variables involved. Another example is when you want to output a byte, unformatted, to an ostream using its put function. Any ideas? Note: I'm still not really convinced. So if you know the definitive answer, you can still post it indeed.

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• Replicating Active Directory - testing scenarios

  - by Naeem Sarfraz

  Replicating a production server's Active Directory is possible through a number of approaches as mentioned here and here. I'm looking for a simpler approach if one exists. I have a mixed-mode authentication site that I need to test. Quite simply AD users (internal) will have more privilege's than someone who logs in via forms (external). We have a web service that cache's an AD structure (users & groups). I'm thinking of building a module (http handler I guess?) that will pick up my specially formed URL (http://impersonateduser@localhost/mywebapp) and use the bit before the @ as the username. That will be the username I use for any subsequent operations. How does that sound? Has anyone got other proposals for testing scenarios like this?

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• pass php array to jquery with getJSON

  - by robertdd

  i want to pass a php aray to jQuery: $.getimagesarr = function() { $.getJSON('operations.php', {'operation':'getimglist'}, function(data){ var arr = new Array(); arr = data; return arr; }); } var data = $.getimagesarr(); if (data){ jQuery.each(data, function(i, val) { .... }); } it return undefined in php i have this: function getimglist(){ $results = $_SESSION['files']; echo json_encode($results); } it is possible?

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• Database structure for storing Bank-like accounts and transactions

  - by user1241320

  We're in the process of adding a bank-like sub-system to our own shop. We already have customers, so each will be given a sort of account and transactions of some kind will be possible (adding to the account or subtracting from it). So we at least need the account entity, the transaction one and operations will then have to recalculate overall balances. How would you structure your database to handle this? Is there any standard bank system have to use that I could mock? By the way, we're on mysql but will also look at some nosql solution for performance boost.

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• CouchDB Versioning / Auditing

  - by Cory

  I'm attempting to use CouchDB for a system that requires full auditing of all data operations. Because of its built in revision-tracking, couch seemed like an ideal choice. But then I read in the O'Reilly textbook that "CouchDB does not guarantee that older versions are kept around." I can't seem to find much more documentation on this point, or how couch deals with its revision-tracking internally. Is there any way to configure couch either on a per-database, or per-document level to keep all versions around forever? If so, how?

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• How can I get jcifs to play nicely with apache axis

  - by Ben Hammond

  I need to connect Apache Axis 1.4 to a Webservice that uses NTLM authentication to restrict access to its operations. I'm expecting to use Samba Jcifs to handle the NTLM handshake. I found http://hc.apache.org/httpcomponents-client/ntlm.html which gives me fantastic directions for how to wire up HttpClient 4.0 with jcifs. Trouble is, Axis wants to use Http Client 3.0 and the two apis look very different. There are 2 possibilities that I can see Write an object for Axis that lets it plug into HttpClient 4. Figure out how to wire HttpClient 3.0 up with Samba Jcifs. Number 1. looks non-trivial, but possible Number 2. I cannot find any encouraging messages on the web describing how to do this. My question is: has anyone successfully connected samba jcifs with HttpClient 3.0 ? Has anyone already created an Axis HttpSender object that works with HttpClient 4 ? Is there some better alternative that I have not considered?

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• Int PK inner join Vs Guid PK inner Join on SQL Server. Execution plan.

  - by bigb

  I just did some testing for Int PK join Vs Guid PK. Tables structure and number of records looking like that: Performance of CRUD operations using EF4 are pretty similar in both cases. As we know Int PK has better performance rather than strings. So SQL server execution plan with INNER JOINS are pretty different Here is an execution plan. As i understand according with execution plan from attached image Int join has better performance because it is taking less resources for Clustered index scan and it is go in two ways, am i right? May be some one may explain this execution plan in more details?

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• What data is actually stored in a B-tree database in CouchDB?

  - by Andrey Vlasovskikh

  I'm wondering what is actually stored in a CouchDB database B-tree? The CouchDB: The Definitive Guide tells that a database B-tree is used for append-only operations and that a database is stored in a single B-tree (besides per-view B-trees). So I guess the data items that are appended to the database file are revisions of documents, not the whole documents: +---------|### ... | | +------|###|------+ ... ---+ | | | | +------+ +------+ +------+ +------+ | doc1 | | doc2 | | doc1 | ... | doc1 | | rev1 | | rev1 | | rev2 | | rev7 | +------+ +------+ +------+ +------+ Is it true? If it is true, then how the current revision of a document is determined based on such a B-tree? Doesn't it mean, that CouchDB needs a separate "view" database for indexing current revisions of documents to preserve O(log n) access? Wouldn't it lead to race conditions while building such an index? (as far as I know, CouchDB uses no write locks).

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• Does my Dictionary must use locking mechanism?

  - by theateist

  Many threads have access to summary. Each thread will have an unique key for accessing the dictionary; Dictionary<string, List<Result>> summary; Do I need locking for following operations? summary[key] = new List<Result>() summary[key].Add(new Result()); It seems that I don't need locking because each thread will access dictionary with different key, but won't the (1) be problematic because of adding concurrently new record to dictionary with other treads?

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• Implementing DRY Forms

  - by virtualeyes

  Getting into Play 2.0, overall, blown away, great stuff. Anyway, wondering how one can achieve DRY forms in Play? If you look at the create & edit examples in the Computer Database Sample, you'll see that the form elements are repeated. With just 4 fields (in the sample form), no big deal, but when you're dealing with large, complex forms and/or handling many CRUD models, the duplication becomes a bigger maintenance issue. On the binding end ( form.bindFromRequest and form.fill(Foo) ), the implementation is so elegant for create/edit operations; is there a corresponding solution in the template layer?

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• What's currently the best way to extend Excel using C#?

  - by user169867

  I have the professional versions of VS2008 & VS2010. I wish to add a couple buttons to a toolbar in Excel. When they are clicked I'd like to be able to open a form (either WinForms or WPF is fine) collect a few values from the user in the form and then take that data + read cell values from the current worksheet to perform some database operations. What's currently the best way to do this using C#? I'd greatly appreciate a pointer to any examples / tutorials. My understanding is that VS2010 has improved the process alot but I may have to deal w/ Excel 2003 which I don't think it supports. I get confused between Visual Studio 2008s Extensibility-Shared Addin template and other Office Addin templates I've seen. I'm not sure when which type of solution is appropriate. I'm new to Office development so I'd really appreciate any help to get me going on the right track. Thanks much.

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• Can I turn off implicit Python unicode conversions to find my mixed-strings bugs?

  - by Tal Weiss

  When profiling our code I was surprised to find millions of calls to C:\Python26\lib\encodings\utf_8.py:15(decode) I started debugging and found that across our code base there are many small bugs, usually comparing a string to a unicode or adding a sting and a unicode. Python graciously decodes the strings and performs the following operations in unicode. How kind. But expensive! I am fluent in unicode, having read Joel Spolsky and Dive Into Python... I try to keep our code internals in unicode only. My question - can I turn off this pythonic nice-guy behavior? At least until I find all these bugs and fix them (usually by adding a u'u')? Some of them are extremely hard to find (a variable that is sometimes a string...). Python 2.6.5 (and I can't switch to 3.x).

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• Performance implications of finalizers on JVM

  - by Alexey Romanov

  According to this post, in .Net, Finalizers are actually even worse than that. Besides that they run late (which is indeed a serious problem for many kinds of resources), they are also less powerful because they can only perform a subset of the operations allowed in a destructor (e.g., a finalizer cannot reliably use other objects, whereas a destructor can), and even when writing in that subset finalizers are extremely difficult to write correctly. And collecting finalizable objects is expensive: Each finalizable object, and the potentially huge graph of objects reachable from it, is promoted to the next GC generation, which makes it more expensive to collect by some large multiple. Does this also apply to JVMs in general and to HotSpot in particular?

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• Letting Wcf data service implement another contract

  - by Wasim

  Hi all , I have a wcf data service with the standart configuration . I want to add another functionality to it , so I built a contract interface and let my wcf data service implements it . Now I see in the service the InitializeService method , and the contract interface methods . When I come to connect the service , I get an error , that there is no end point declared to the contract I added . How can do that ? examples ? links ? I choosed to add the contract interface to the wcf data service and not adding another service , because the client application uses the wcf data service generated objects , and I want to use the same obkject to make operations not related to data , for more coplex processing . If I do the methods in another service , then I have types incompatibility . Thanks in advance ...

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• A datastructure for Robotic Sort

  - by amit.codename13

  I am trying to solve this problem : https://www.spoj.pl/problems/CERC07S/ I have identified that i need a datastructure in which reversing operations have lesser time complexity. I tried to create one using a doubly linked list, in which (i thought) reversing can be done in O(1) by just changing a value associated with the starting and ending node which indicates the direction of traversing the list. I tried to implement it but got stuck. Maybe the approach is wrong! Are trees applicable here? If yes, how? Any ideas or links are appreciated? Thanks in advance.

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• Primary reasons why programming language runtimes use stacks?

  - by manuel aldana

  Many programming language runtime environments use stacks as their primary storage structure (e.g. see JVM bytecode to runtime example). Quickly recalling I see following advantages: Simple structure (pop/push), trivial to implement Most processors are anyway optimized for stack operations, so it is very fast Less problems with memory fragmentation, it is always about moving memory-pointer up and down for allocation and freeing complete blocks of memory by resetting the pointer to the last entry offset. Is the list complete or did I miss something? Are there programming language runtime environments which are not using stacks for storage at all?

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• Can this loop be sped up in pure Python?

  - by Noctis Skytower

  I was trying out an experiment with Python, trying to find out how many times it could add one to an integer in one minute's time. Assuming two computers are the same except for the speed of the CPUs, this should give an estimate of how fast some CPU operations may take for the computer in question. The code below is an example of a test designed to fulfill the requirements given above. This version is about 20% faster than the first attempt and 150% faster than the third attempt. Can anyone make any suggestions as to how to get the most additions in a minute's time span? Higher numbers are desireable. EDIT: This experiment is being written in Python 3.1 and is 15% faster than the fourth speed-up attempt. def start(seconds): import time, _thread def stop(seconds, signal): time.sleep(seconds) signal.pop() total, signal = 0, [None] _thread.start_new_thread(stop, (seconds, signal)) while signal: total += 1 return total if __name__ == '__main__': print('Testing the CPU speed ...') print('Relative speed:', start(60))

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• C++ Thread Safe Integer

  - by Paul Ridgway

  Hello everyone, I have currently created a C++ class for a thread safe integer which simply stores an integer privately and has public get a set functions which use a boost::mutex to ensure that only one change at a time can be applied to the integer. Is this the most efficient way to do it, I have been informed that mutexes are quite resource intensive? The class is used a lot, very rapidly so it could well be a bottleneck... Googleing C++ Thread Safe Integer returns unclear views and oppinions on the thread safety of integer operations on different architectures. Some say that a 32bit int on a 32bit arch is safe, but 64 on 32 isn't due to 'alignment' Others say it is compiler/OS specific (which I don't doubt). I am using Ubuntu 9.10 on 32 bit machines, some have dual cores and so threads may be executed simultaneously on different cores in some cases and I am using GCC 4.4's g++ compiler. Thanks in advance...

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• Sql Server 2000 Stored Procedure Prevent Parallelism or something?

  - by user187305

  I have a huge disgusting stored procedure that wasn't slow a couple months ago, but now is. I barely know what this thing does and I am in no way interested in rewriting it. I do know that if I take the body of the stored procedure and then declare/set the values of the parameters and run it in query analyzer that it runs more than 20x faster. From the internet, I've read that this is probably due to a bad cached query plan. So, I've tried running the sp with "WITH RECOMPILE" after the EXEC and I've also tried putting the "WITH RECOMPLE" inside the sp, but neither of those helped even a little bit. When I look at the execution plan of the sp vs the query, the biggest difference is that the sp has "Parallelism" operations all over the place and the query doesn't have any. Can this be the cause of the difference in speeds? Thank you, any ideas would be great... I'm stuck.

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• ContextSwitchDeadlock Was Detected error in C#

  - by assassin

  Hi, I am running a C# application, and during run-time I get the following error: The CLR has been unable to transition from COM context 0x20e480 to COM context 0x20e5f0 for 60 seconds. The thread that owns the destination context/apartment is most likely either doing a non pumping wait or processing a very long running operation without pumping Windows messages. This situation generally has a negative performance impact and may even lead to the application becoming non responsive or memory usage accumulating continually over time. To avoid this problem, all single threaded apartment (STA) threads should use pumping wait primitives (such as CoWaitForMultipleHandles) and routinely pump messages during long running operations. Can anyone please help me out with the problem here? Thanks a lot.

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• How to implement square root and exponentiation on arbitrary length numbers?

  - by tomp

  I'm working on new data type for arbitrary length numbers (only non-negative integers) and I got stuck at implementing square root and exponentiation functions (only for natural exponents). Please help. I store the arbitrary length number as a string, so all operations are made char by char. Please don't include advices to use different (existing) library or other way to store the number than string. It's meant to be a programming exercise, not a real-world application, so optimization and performance are not so necessary. If you include code in your answer, I would prefer it to be in either pseudo-code or in C++. The important thing is the algorithm, not the implementation itself. Thanks for the help.

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• How might one implement FileTimeToSystemTime?

  - by Billy ONeal

  Hello :) I'm writing a simple wrapper around the Win32 FILETIME structure. boost::datetime has most of what I want, except I need whatever date type I end up using to interpolate with Windows APIs without issues. To that end, I've decided to write my own things for doing this -- most of the operations aren't all that complicated. I'm implementing the TimeSpan - like type at this point, but I'm unsure how I'd implement FileTimeToSystemTime. I could just use the system's built-in FileTimeToSystemTime function, except FileTimeToSystemTime cannot handle negative dates -- I need to be able to represent something like "-12 seconds". How should something like this be implemented? Billy3

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• Help me understand Dispose() implementation code from MSDN

  - by Benny

  the following code is from MSDN: Idisposable pattern protected virtual void Dispose(bool disposing) { // If you need thread safety, use a lock around these // operations, as well as in your methods that use the resource. if (!_disposed) { if (disposing) { if (_resource != null) _resource.Dispose(); Console.WriteLine("Object disposed."); } // Indicate that the instance has been disposed. _resource = null; _disposed = true; } } why the following statement: _resource = null; _disposed = true; are not enclosed by if (disposing) statement block? for me i would probably write like this: if (disposing) { if (_resource != null) { _resource.Dispose(); _resource = null; _disposed = true; } Console.WriteLine("Object disposed."); } anything wrong with my version?

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