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• Language Agnositc Basic Programming Question

  - by Rachel

  This is very basic question from programming point of view but as I am in learning phase, I thought I would better ask this question rather than having an misunderstanding or narrow knowledge about the topic. So do excuse me if somehow I mess it up. Question: Let say I have class A,B,C and D now class A has some piece of code which I need to have in class B,C and D so I am extending class A in class B, class C, and class D Now how can I access the function of class A in other classes, do I need to create an object of class A and than access the function of class A or as am extending A in other classes than I can internally call the function using this parameter. If possible I would really appreciate if someone can explain this concept with code sample explaining how the logic flows.

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• How do I use a shared library (in this case JsonCpp) in my C++ program on Linux?

  - by Not Joe Bloggs

  I'm a new-ish C++ programmer, and I'm doing my first program on my own using C++. I decided I would like to use JSON to store some of the data I'm going to be using, and I've found a library to handle JSON, JsonCpp. I've installed the library using my Linux system's package manager, and in my C++ code, I've used in my source code file #include <json> and compiled it using g++ and it's -ljson and -L/usr/lib options (libjson.so is located in /usr/lib). However, the first usage of Json::Value, an object provided by the library, gives a compilation error of "Json has not declared". I'm sure my mistake is something simple, so could someone explain what I'm doing wrong? None of the books I had mention how to use shared libraries, so I've had to google to find this much.

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• 80x86 16-bit asm: lea cx, [cx*8+cx] causes error on NASM (compiling .com file)

  - by larz

  Title says it all. The error NASM gives (dispite my working OS) is "invalid effective address". Now i've seen many examples of how to use LEA and i think i gots it right but yet my NASM dislikes it. I tried "lea cx, [cx+9]" and it worked; "lea cx, [bx+cx]" didn't. Now if i extended my registers to 32-bits (i.e. "lea ecx, [ecx*8+ecx]") everything would be well but i am restricted to use 16- and 8-bit registers only. Is here anyone so knoweledgeable who could explain me WHY my assembler doesn't let me use lea the way i supposed it should be used? Thanks.

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• I cant really wrap my head around BOOLEAN logic when I use NOT together with AND and OR

  - by Bq

  Im trying to understand how boolean logic works when I use NOT. To give an example using awk I have a text file containing CORE PORT CORE PORT COREPORT CORE COREPORT And I would like to remove all COREPORT lines. The way I thought I would do it was with (NOT CORE) AND (NOT PORT) eg awk '/!CORE/&&/!PORT/{print}' But when I try it out Im actually supposed to use OR instead of AND awk '/!CORE/||/!PORT/{print}' I would be really glad if some one could explain where my thinking is wrong and super glad if it could be visualized with a venn diagram or something like the boolean machine at kathyschrock

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• LINQ: why does this query not work on an ArrayList?

  - by Benny

  public static ArrayList GetStudentAsArrayList() { ArrayList students = new ArrayList { new Student() { RollNumber = 1,Name ="Alex " , Section = 1 ,HostelNumber=1 }, new Student() { RollNumber = 2,Name ="Jonty " , Section = 2 ,HostelNumber=2 } }; return students; } The following code doesn't compile. The error is ArrayList is not IEnumerable ArrayList lstStudents = GetStudentAsArrayList(); var res = from r in lstStudents select r; This compiles: ArrayList lstStudents = GetStudentAsArrayList(); var res = from Student r in lstStudents select r; Can anybody explain what the difference is between these two snippets? Why the second works?

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• Height of tableHeaderView seems to be 0

  - by gabac

  I tried to override the second tableHeaderView. But it seems that the height of it in the method heightForHeaderInSection seems to be 0. Can't explain it, do I have to put it in a iVar because in the viewForHeaderInSection I can set the view without any problems. - (NSString *)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section { if(section == 0) return @"Adding a new list"; else return @"Other lists"; } - (UIView *)tableView:(UITableView *)tableView viewForHeaderInSection:(NSInteger)section { if(section == 0) { return tableView.tableHeaderView; } else { UIView *view = [[[UIView alloc] initWithFrame:CGRectMake(10, 10, 100, 50)] autorelease]; view.backgroundColor = [UIColor redColor]; return view; } } - (CGFloat)tableView:(UITableView *)tableView heightForHeaderInSection:(NSInteger)section { if(section == 0) return tableView.tableHeaderView.frame.size.height; else return 30; }

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• Methods in super that will be subclassed anyway (Cocoa)

  - by Michael Matheus

  Sorry if this is a repost but I couldn't quite search for it because I can't explain it in a few words. I have a super class with lots of methods but they will always (not all of them) be subclassed. From the super I need to access (read only) those methods. I could either leave the methods in super empty or I could just not type them in super but call them anyway like so [self myMethod] and it will call my subclassed method even if it doesn't exist in super. This works but Xcode gives me an error though. 'superclass' may not respond to '-subclassmethod' What should I do?

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• I dont understand how Westpac Payway API and NET works

  - by spirytus

  Been googling all day, reading numerous pdf's and still getting confused with the concepts of sending data to Payway system from Westpac (bank in Australia, link text). They offer access via API but also give access via what they call NET. The way I understand is that when client want to pay on my website, in case of NET, client gets to the page (hosted by a bank or hosted by me) where is provided with form to enter credit card info details. Then this form is submitted via normal POST call to Payway's specific https address. It is processed then and browser returns to url I specified as one of the parameters I sent in hidden field. In case of API story is similar, so user receives form, fills in the data and then data is send to my backend (not Payway's). My backend then calls payway API with data provided and once answer received returns confirmation page to the client. Is my understanding right? Please explain as I have a feeling I am missing something basic here.

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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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• 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 is the 'if' statement considered evil?

  - by Vadim

  I just came from Simple Design and Testing Conference. In one of the session we were talking about evil keywords in programming languages. Corey Haines, who proposed the subject, was convinced that if statement is absolute evil. His alternative was to create functions with predicates. Can you please explain to me why if is evil. I understand that you can write very ugly code abusing if. But I don't believe that it's that bad.

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• Tokenize problem in Java with separator ". "

  - by user112976

  I need to split a text using the separator ". ". For example I want this string : Washington is the U.S Capital. Barack is living there. To be cut into two parts: Washington is the U.S Capital. Barack is living there. Here is my code : // Initialize the tokenizer StringTokenizer tokenizer = new StringTokenizer("Washington is the U.S Capital. Barack is living there.", ". "); while (tokenizer.hasMoreTokens()) { System.out.println(tokenizer.nextToken()); } And the output is unfortunately : Washington is the U S Capital Barack is living there Can someone explain what's going on?

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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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• ajax parameter to send correctly a variable to a specified url

  - by kawtousse

  I am trying to send data to a servlet from a js file but the servlet never received the parameter. so this is what I have: function showProject(prj) { xmlhttp=GetXmlHttpObject(); if (xmlhttp==null) { alert ("Browser does not support HTTP Request"); return; } var url="ServletxmlGenerator"; idprj = prj.options[prj.selectedIndex].value; //alert(idprj); url=url+"?idprj="+idprj; xmlhttp.onreadystatechange=stateChanged; xmlhttp.open("GET",url,true); xmlhttp.send(null); } and to capture th request it is with: public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { String projectcode=request.getParameter("idprj"); System.out.println("++++projectCode:=" +projectcode); the output is like: ++++projectCode:=null Can any one explain it to me it seems to be correct but i didnot find the error.Thinks

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• Spring bean's DESTROY-METHOD attribute [does not work for me]

  - by EugeneP

  Can get work the attribute "destroy-method". First, even if I type non-existing method name into "destroy-method" attribute, Spring initialization completes fine (already strange!). Next, when a bean has a "prototype" scope, then I suppose it must be destroyed before the application is closed. That not happens, it is simply never called in my case. Though, after extracting this bean I can call this method explicitly and it does its job. Could you explain why this method is never called in my Spring 2.5 case? p.s. The method exists, it is public and has no arguments.

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• CORBA Naming Service returns incorrect location of a registered object

  - by dave-keiture

  Hi experts, I have a simple setup with several objects registered at orbd. Remote client initializes connection to the ORB and tries to resolve a reference to the Naming Serice (IDL:omg.org/CosNaming/NamingContextExt:1.0). So far it's all fine - ORB returns giop.iiop.host/giop.iiop.port pair. When reference to the Naming Service is resolved, client tries to resolve_str() one of the registered objects. This time, Naming Service returns completely different pair giop.iiop.host/giop.iiop.port for the object (not the host/port of a Naming Service) - I don't know anything about them. When client tries to call a method on a resolved object, it fails, as the host/port pair is not configured in the firewall. Could you please explain, why it's happening? Thanks in advance!

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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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• Single HTML Table from multiple MySQL tables

  - by David Chouinard

  Hi! I've been struggling for a while with this one; I'll try to explain it here as simply as possible. Consider this MySQL table: +----------+-----------+---------+--------+ |status_id |session_id |pilot_id |present | +----------+-----------+---------+--------+ |1 |61 |901 |1 | |2 |63 |901 |1 | |3 |62 |901 |0 | |4 |62 |902 |1 | |5 |63 |903 |1 | +----------+-----------+---------+--------+ Both session_id and pilot_id are foreign keys making reference to a primary key in another table. The same pilot_id can be associated with different session_id, but every pilot_id-session_id combination is unique. I need to make an HTML table (in PHP) that would display the data like this: +----------+---------+---------+---------+ | |61 |62 |63 | +----------+---------+---------+---------+ |901 |X | |X | |902 | |X | | |903 | | |X | +----------+---------+---------+---------+ Hence, rows are pilot_id and columns are session_id. When a pilot_id-session_id combination has a present value of 1, the corresponding cell should be checked. (ie. when the row-combination is zero or the combination does not exist in the MySQL table, nothing should appear in the HTML table) Phew. Any ideas? Thanks!

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• TypeError: Python thinks that I passed a function 2 arguments but I only passed it 1

  - by slhck

  I work on something in Seattle Repy which is a restricted subset of Python. Anyway, I wanted to implement my own Queue that derives from a list: class Queue(list): job_count = 0 def __init__(self): list.__init__(self) def appendleft(item): item.creation_time = getruntime() item.current_count = self.job_count self.insert(0, item) def pop(): item = self.pop() item.pop_time = getruntime() return item Now I call this in my main server, where I use my own Job class to pass Jobs to the Queue: mycontext['queue'] = Queue() # ... job = Job(str(ip), message) mycontext['queue'].appendleft(job) The last line raises the following exception: Exception (with type 'exceptions.TypeError'): appendleft() takes exactly 1 argument (2 given) I'm relatively new to Python, so could anyone explain to me why it would think that I gave appendleft() two arguments when there obviously was only one?

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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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• set variables in an MVC application?

  - by Melissa

  I am trying to learn about the Orchard MVC application. I see the following code but cannot understand what it is doing. Can someone explain what this: User.As<UserPart>().Record.UserName = value; means? public class UserEditViewModel { [Required] public string UserName { get { return User.As<UserPart>().Record.UserName; } set { User.As<UserPart>().Record.UserName = value; } } [Required] public string Email { get { return User.As<UserPart>().Record.Email; } set { User.As<UserPart>().Record.Email = value; } } public IContent User { get; set; } }

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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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• 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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• Python sys.argv lists and indexes

  - by Fred Gerbig

  In the below code I understand that sys.argv uses lists, however I am not clear on how the index's are used here. def main(): if len(sys.argv) >= 2: name = sys.argv[1] else: name = 'World' print 'Hello', name if __name__ == '__main__': main() If I change name = sys.argv[1] to name = sys.argv[0] and type something for an argument it returns: Hello C:\Documents and Settings\fred\My Documents\Downloads\google-python-exercises \google-python-exercises\hello.py Which kind of make sense. Can someone explain how the 2 is used here: if len(sys.argv) >= 2: And how the 1 is used here: name = sys.argv[1]

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• Limitation of Attachment size when using SMTP

  - by Gas Gemba

  Hi, I wrote a C++ program to send a mail using SMTP. But when I attach any files I notices that a single file's size always is limited to 808 bytes. As an example if I send a text file with 10 KBs, when I download the attachment it has only text worth 808 bytes. If the large file is a zip file, it gets corrupted in unzipping obviously due to CRC failure. I used a MAPI library to send larger files without a problem. Is this a network limitation of SMTP? Can someone please explain why this is happening?? Thank You!!!

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