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• what is a data serialization system?

  - by Yang

  according to Apache AVRO project, "Avro is a serialization system". By saying data serialization system, does it mean that avro is a product or api? also, I am not quit sure about what a data serialization system is? for now, my understanding is that it is a protocol that defines how data object is passed over the network. Can anyone help explain it in an intuitive way that it is easier for people with limited distributed computing background to understand? Thanks in advance!

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• Java method overloading + double dispatch

  - by Max

  Can anybody explain in detail the reason the overloaded method print(Parent parent) is invoked when working with Child instance in my test piece of code? Any pecularities of virtual methods or methods overloading/resolution in Java involved here? Any direct reference to Java Lang Spec? Which term describes this behaviour? Thanks a lot. public class InheritancePlay { public static class Parent { public void doJob(Worker worker) { System.out.println("this is " + this.getClass().getName()); worker.print(this); } } public static class Child extends Parent { } public static class Worker { public void print(Parent parent) { System.out.println("Why this method resolution happens?"); } public void print(Child child) { System.out.println("This is not called"); } } public static void main(String[] args) { Child child = new Child(); Worker worker = new Worker(); child.doJob(worker); } }

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• What is going on with the "return fibonacci( number-1 ) + fibonacci( number-2 )"?

  - by user1478598

  I have problem understanding what the return fibonacci( number-1 ) + fibonacci( number-2 ) does in the following program: import sys def fibonacci( number ): if( number <= 2 ): return 1 else: return fibonacci( number-1 ) + fibonacci( number-2 ) The problem is that I can't imagine how this line works: return fibonacci( number-1 ) + fibonacci( number-2 ) Does the both of the "fibonacci( number-1 )" and "fibonacci( number-2 )" being processed at the same time? or the "fibonacci( number-1 )" is the first to be processed and then the second one? I only see that processing both of them would eventually return '1' so the last result I expect to see it is a '1 + 1' = '2' I would appreciate a lot, If someone can elaborately explain the process of its calculation. I think this is a very newb question but I can't really get a picture of its process.

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• Open Source Code Integrity - How does quality assurance work?

  - by rockinthesixstring

  I've thought about this before and this topic has often steered me away from Open Source projects. Recently DotNetPanel has changed it's name to WebSitePanel and gone Open Source. The rumor mill is speculating that Microsoft is behind this. My question (in multi-part) is quite simple. Can somebody please explain to me how quality assurance works on Open Source projects? How can a closed application get "only better" when Open Source? Doesn't the "too many cooks in the kitchen" theory apply when too many developers contribute (possibly bad) code to a project?

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• opencv image conversion from rgb to hsv

  - by kaushalyjain

  When I run this following code on a sample image ie an rgb image; and then execute it to display the converted hsv image, both appear to be different... can anyone explain why? or can you suggest a solution for this not to happen... coz its the same image afterall Mat img_hsv,img_rgb,red_blob,blue_blob; img_rgb = imread("pic.png",1); cvtColor(img_rgb,img_hsv,CV_RGB2HSV); namedWindow("win1", CV_WINDOW_AUTOSIZE); imshow("win1", img_hsv);

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• Two '==' equality operators in same 'if' condition are not working as intended.

  - by Manav MN

  I am trying to establish equality of three equal variables, but the following code is not printing the obvious true answer which it should print. Can someone explain, how the compiler is parsing the given if condition internally? #include<stdio.h> int main() { int i = 123, j = 123, k = 123; if ( i == j == k) printf("Equal\n"); else printf("NOT Equal\n"); return 0; } Output: manav@workstation:~$ gcc -Wall -pedantic calc.c calc.c: In function ‘main’: calc.c:5: warning: suggest parentheses around comparison in operand of ‘==’ manav@workstation:~$ ./a.out NOT Equal manav@workstation:~$ EDIT: Going by the answers given below, is the following statement okay to check above equality? if ( (i==j) == (j==k))

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• Why Eventmachine Defer slower than Ruby Thread?

  - by allenwei

  I have two scripts which using mechanize to fetch google index page. I assuming Eventmachine will faster than ruby thread, but not. Eventmachine code cost "0.24s user 0.08s system 2% cpu 12.682 total" Ruby Thread code cost "0.22s user 0.08s system 5% cpu 5.167 total " Am I use eventmachine in wrong way? Who can explain it to me, thanks! 1 Eventmachine require 'rubygems' require 'mechanize' require 'eventmachine' trap("INT") {EM.stop} EM.run do num = 0 operation = proc { agent = Mechanize.new sleep 1 agent.get("http://google.com").body.to_s.size } callback = proc { |result| sleep 1 puts result num+=1 EM.stop if num == 9 } 10.times do EventMachine.defer operation, callback end end 2 Ruby Thread require 'rubygems' require 'mechanize' threads = [] 10.times do threads << Thread.new do agent = Mechanize.new sleep 1 puts agent.get("http://google.com").body.to_s.size sleep 1 end end threads.each do |aThread| aThread.join end

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• Releasing NSData causes exception...

  - by badmanj

  Hi, Can someone please explain why the following code causes my app to bomb? NSData *myImage = UIImagePNGRepresentation(imageView.image); : [myImage release]; If I comment out the 'release' line, the app runs... but a few times calling the function containing this code and I get a crash - I guess caused by a memory leak. Even if I comment EVERYTHING else in the function out and just leave those two lines, when the release executes, the app crashes. I'm sure this must be a newbie "you don't know how to clean up your mess properly" kind of thing ;-) Cheers, Jamie.

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• Why does gcc add symbols to non-debug build?

  - by Matt Holgate

  When I do a release build with gcc (i.e. I do not specify -g), I still seem to end up with symbols in the binary, and have to use strip to remove them. In fact, I can still breakpoint functions and get backtraces in gdb (albeit without line numbers). This surprised me - can anyone explain why this happens? e.g. #include <stdio.h> static void blah(void) { printf("hello world\n"); } int main(int argc, char *argv[]) { blah(); return 0; } gcc -o foo foo.c nm foo | grep blah: 08048374 t blah

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• overriding protected internal with protected!

  - by Asad Butt

  This is an extension for this question asked an hour ago. We cannot modify the access modifiers, when overriding a virtual method in derived class. Consider Control class in System.Web.UI namespace public class Control : IComponent, IDisposable,... { protected internal virtual void CreateChildControls() { } . . } Now Consider This public class someClass : System.Web.UI.Control { // This should not compile but it does protected override void CreateChildControls() { } // This should compile but it does not protected internal override void CreateChildControls() { } } can any body explain this ? Thanks

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• problem in basic implementation of MVVM pattern - Services

  - by netmajor

  I watch some video and read articles about MVVM pattern and start thinking how should I implement it in my Silverlight app. So at first I create Silverlight application. I think that for clear view I create 3 folders: View - for each user control page in my app, ViewModel - for c# class which will querying date and Model- Entity Data Model of my SQL Server or Oracle Database. And now I am confused, cause I want to implement *WCF/RIA Services/Web services* in my project. In which folder should I put in class of services? I see in examples that Services take date and filtering it and then output data was binding in View - so It looks as ViewModel. But I was sure that someone use Services in Model and that I want to do. But how? Can someone explain me implementing Services as Model? Is my point of view at MVVM is correctly?

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• Delphi, Csv,Import Firebird

  - by Vijesh V.Nair

  Lemme explain my problem. I have One ID and 2 Other Fields in a CsV file. the ID connected to a database table. I have to show the curresponding entries in the db and fields from Csv. Need sort the Fields too. My Idea was load into a ClientDataset, lookup to a Query with table and Use sort and show. My Csv have 85 K Records and its taking 120 seconds to load and sort, Its not acceptable. Can you tell me, can I use Bacthmove for this. So I can easily pick fields by a simple query. if I can use Bacthmove Plz give me the guild lines. Also Is there any other Techniques for this? Thanks and Regards, Vijesh V.Nair

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• No whitespace between a cast and a namespace operator?

  - by Pod

  Hello. Could anyone please explain the following line of code, found on http://docs.openttd.org/ai__cargo_8cpp_source.html return (AICargo::TownEffect)::CargoSpec::Get(cargo_type)->town_effect; If this line was: return (AICargo::TownEffect) ::CargoSpec::Get(cargo_type)->town_effect; (note the space between TownEffect) and the ::) then I would understand it fine. However there is no whitespace in that document*, which would mean (AICargo::TownEffect) is the left operand of the :: operator. How does this code work/compile? Or are the two things equivilent due to some obscure C++ rule? *It's the same in the cpp file as well.

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• Stop VBA Evaluate from calling target function twice

  - by Abiel

  I am having trouble getting VBA's Evaluate() function to only execute once; it seems to always run twice. For instance, consider the trivial example below. If we run the RunEval() subroutine, it will call the EvalTest() function twice. This can be seen by the two different random numbers that get printed in the immediate window. The behavior would be the same if we were calling another subroutine with Evaluate instead of a function. Can someone explain how I can get Evaluate to execute the target function once instead of twice? Thank you. Sub RunEval() Evaluate "EvalTest()" End Sub Public Function EvalTest() Debug.Print Rnd() End Function

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• Why can XSLT not parse this XML?

  - by Matt W

  Taking the XSLT and XML from this page as an example: http://www.w3schools.com/xsl/xsl_transformation.asp I have an xml file which contains (above example modified): <?xml version="1.0" encoding="ISO-8859-1"?> <?xml-stylesheet type="text/xsl" href="cdcatalog.xsl"?> <catalog xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns="http://tempuri.org/"> <cd> In my case, the output contains nothing when the XSLT/XML is processed by the browser. The moment I remove the attributes from the element, it works. Problem is, I don't really have the option of pre-processing those attributes out of the file. Can anyone explain how to force the XSLT to work with the XML as is, please? After all, those attributes seem fairly standard. Many thanks, Matt.

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• SQL - Counting sets of Field-B values for each Field-A value

  - by potrnd

  Hello, First of all sorry that I could not think of a more descriptive title. What I want to do is the following using only SQL: I have some lists of strings, list1, list2 and list3. I have a dataset that contains two interesting columns, A and B. Column A contains a TransactionID and column B contains an ItemID. Naturally, there can be multiple rows that share the same TransactionIDs. I need to catch those transactions that have at least one ItemID in each and every list (list1 AND list2 AND list3). I also need to count how many times does that happen for each transaction. [EDIT] That is, count how many full sets of ItemIDs there are for each TransactionID", "Full Set" being any element of the list1 with any element of the list2 with any element of the list3 I hope that makes enough sense, perhaps I will be able to explain it better with a clear head. Thanks in advance

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• Why is this codes output an Error?

  - by Ari Susanto

  I am a newbie on php writing. In the my first trying, I get a problem on input a html tag to php. This code output an error: <?php $a="Begin"; $b=12; echo $b . " " . $a . " " . "This is php file <br/>"; echo strlen($a); echo strpos($a,"in") . "<br/>"; echo addcslashes($a,"i")"; ?> this is the error message I get: Parse error: syntax error, unexpected '"', expecting ',' or ';' in /home/specials/public_html/bextool.com/1.php on line 7 Is there any body who can explain about it?

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• How do I add a static library target that compiles before an application compiles in Xcode?

  - by Koning Baard XIV

  I'm creating a static library in C++. The static library itself links to nothing. To test the static library, I'm creating a test program in C++ (you know, with a main function). Now, I want that whenever I click Build in Xcode, it compiles the static library first, then compiles the test program and link that test program to the static library, like this: # The steps indicate the order Xcode should compile it # (Step 1) Static Library <----------. | (Step 2) Test Program -------> Standard Library Also, the test program should use the header files of the static library. Can anyone explain me how to configure this in Xcode? Thanks

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• Office Interop addins installer?

  - by jimbojw

  I have three C# Solutions in Visual Stuido 2008, one each for Word, Excel and PowerPoint using interop to hook various events. In each Solution, I have exactly one class, the one created by default when using File - New - Project - Visual C# - Office - 2007. Now that I have my addins working properly, it's time to create an installer. I understand that I may also have to distribute the PIAs. I would like my installer to register itself such that it can be uninstalled via the normal Add/Remove Programs mechanism. My organization is somewhat standardized around WiX for creating installers, but I'm open to any suggestions. How do I produce an MSI or EXE capable of installing my addins? GUI/wizard for the installer is not necessary. I'm happy to RTFM - so far all the tutorials I've found only explain how to create the project and do some of the coding. Maybe I'm using the wrong search terms? Thanks in advance for any help!

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• Copy constructor demo (crashing... case 2)

  - by AKN

  Please have a glance at this program: class CopyCon { public: char *name; CopyCon() { name = new char[20]; name = "Hai";//_tcscpy(name,"Hai"); } CopyCon(const CopyCon &objCopyCon) { name = new char[_tcslen(objCopyCon.name)+1]; _tcscpy(name,objCopyCon.name); } ~CopyCon() { if( name != NULL ) { delete[] name; name = NULL; } } }; int main() { CopyCon obj1; CopyCon obj2(obj1); cout<<obj1.name<<endl; cout<<obj2.name<<endl; } This program crashes on execution. Error: "Expression: _BLOCK_TYPE_IS_VALID(pHead-nBlockUse)" If I assign "Hai" to name using aasignment operator, its crashing. Where as when I use string func _tcscpy to assign "Hai" to name, its working perfectly. Can some one explain why so?

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• can't insert xml dml expression as a string

  - by 81967

  Here is the code below that would explain you the problem... I create a table below with an xml column and declare a variable, initialize it and Insert the Value into the xml column, create table CustomerInfo (XmlConfigInfo xml) declare @StrTemp nvarchar(2000) set @StrTemp = '<Test></Test>' insert into [CustomerInfo](XmlConfigInfo) values (@StrTemp) Then comes the part of the question,, if I write this... update [CustomerInfo] set XmlConfigInfo.modify('insert <Info></Info> into (//Test)[1]') -- Works Fine!!! but when I try this, set @StrTemp = 'insert <Info></Info> into (//Test)[1]' update [CustomerInfo] set XmlConfigInfo.modify(@StrTemp) -- Doesn't Work!!! and throws an error The argument 1 of the xml data type method "modify" must be a string literal. is there a way around for this one? I tried this, but it is not working :(

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• Use the [Serializable] attribute or subclassing from MarshalByRefObject?

  - by Theo Lenndorff

  I'd like to use an object across AppDomains. For this I can use the [Serializeable] attribute: [Serializable] class MyClass { public string GetSomeString() { return "someString" } } Or subclass from MarshalByRefObject: class MyClass: MarshalByRefObject { public string GetSomeString() { return "someString" } } In both cases I can use the class like this: AppDomain appDomain = AppDomain.CreateDomain("AppDomain"); MyClass myObject = (MyClass)appDomain.CreateInstanceAndUnwrap( typeof(MyClass).Assembly.FullName, typeof(MyClass).FullName); Console.WriteLine(myObject.GetSomeString()); Why do both approaches seem to have the same effect? What is the difference in both approaches? When should I favor the one approach over the other? EDIT: At the surface I know that there are differences between both mechanisms, but if someone jumped out of a bush and asked me the question I couldn't give him a proper answer. The questions are quite open questions. I hoped that someone can explain it better than I could do.

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• MySQL Export with Column Heading

  - by st4nt0n

  Hello - I am very, very, new to mySQL. I've got experience in general technical terms, but not with the syntax or concepts of mySQL. I have been tasked with exporting a table from MySQL into a pipe delimited .txt or .xls that I can use to add 7500 more records to manually, then import back into the table. I tried to use INTO OUTFILE, but I don't get column headings, which I need for reference to merge the new records. Is there a good resource that can explain this to a complete novice? I would usually go down to my bookstore and start learning, but I'm on a bit of a time crunch. Thanks all!

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• Different results when applying function to equal values

  - by Johannes Stiehler

  I'm just digging a bit into Haskell and I started by trying to compute the Phi-Coefficient of two words in a text. However, I ran into some very strange behaviour that I cannot explain. After stripping everything down, I ended up with this code to reproduce the problem: let sumTup = (sumTuples°concat) frequencyLists let sumFixTup = (138, 136, 17, 204) putStrLn (show ((138, 136, 17, 204) == sumTup)) putStrLn (show (phi sumTup)) putStrLn (show (phi sumFixTup)) This outputs: True NaN 0.4574206676616167 So although the sumTupand sumFixTup show as equal, they behave differently when passed to phi. The definition of phi is: phi (a, b, c, d) = let dividend = fromIntegral(a * d - b * c) divisor = sqrt(fromIntegral((a + b) * (c + d) * (a + c) * (b + d))) in dividend / divisor

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• Code to make div appear after a certain amount of time.

  - by user307783

  Hi, I'm looking for code that makes a div appear after a certain amount of time on a site. Here's the sort of thing I'm talking about: <div class="container"> <div class="secretpopout"> This is the div I want to pop out after a couple of minutes. </div> </div> I'm relatively new to javascript and jQuery, but I'm assuming I will need to use the setTimeout or something similar. I've tried finding the answer online, but if someone could explain it in a way a designer (as opposed to a programmer) would get it, that would be great - ANY LIGHT shed on this would be greatly appreciated. Thank you.

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