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• In ArrayBlockingQueue, why copy final member field into local final variable?

  - by mjlee

  In ArrayBlockingQueue, any method that requires lock will get set 'final' local variable before calling 'lock()'. public boolean offer(E e) { if (e == null) throw new NullPointerException(); final ReentrantLock lock = this.lock; lock.lock(); try { if (count == items.length) return false; else { insert(e); return true; } } finally { lock.unlock(); } } Is there any reason to set a local variable 'lock' from 'this.lock' when field 'this.lock' is final also. Additionally, it also set local variable of E[] before acting on. private E extract() { final E[] items = this.items; E x = items[takeIndex]; items[takeIndex] = null; takeIndex = inc(takeIndex); --count; notFull.signal(); return x; } Is there any reason for copying to local final variable?

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• Cannot get MEDIA_URL from Django widget's template

  - by Eric

  Hi folks, I am a new Djangoer, and figuring out how to build custom widget, my problem is cannot get the MEDIA_URL in my widget's template, while the form use MySelectWidget able to get the MEDIA_URL itself. # #plus_sign.html # <a href="" class="" id="id_{{ field }}"> <img src="{{ MEDIA_URL }}images/plus_sign.gif" width="10" height="10" alt="Add"/> </a> *^ cannot load the {{ MEDIA_URL}} to this widget's template, and therefore I can't load the .gif image properly. :(* # #custom_widgets.py # from django import forms class MySelectMultiple(forms.SelectMultiple): def render(self, name, *args, **kwargs): html = super(MySelectMultiple, self).render(name, *args, **kwargs) plus = render_to_string("plus_sign.html", {'field': name}) return html+plus # #forms.py # from django import forms from myapp.custom_widgets.py import MySelectMultiple class MyForm(forms.ModelForm): contacts = forms.ModelMultipleChoiceField(Contact.objects, required=False, widget=MySelectMultiple) # #views.py # def AddContacts(request): if request.method == 'POST': form = MyForm(request.POST) if form.is_valid(): cd = form.cleaned_data new = form.save() return HttpResponseRedirect('/addedContact/') else: form = MyForm() return render_to_response('shop/my_form.html', {'form': form}, context_instance=RequestContext(request)) # #my_form.html # {% extends "base.html" %} {% block content %} {{ form.contacts }} {% endblock %} Please let me know how can I load the widget's image properly. Thank you so much for all responses.

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• Cached data accessed by reference?

  - by arthurdent510

  I am running into an odd problem, and this is the only thing I can think of. I'm storing a list in cache, and I am randomly losing items from my list as users use the site. I have a class that is called that either goes to cache and returns the list from there, or if the cache is over a certain time frame old, it goes to the database and refreshes the cache. So when I pull the data from cache, this is what it looks like.... results = (List<Software>)cache["software"]; And then I return results and do some processing, filter for security, and eventually it winds up on the screen. For each Software record, there can be multiple resources attached to it, and based on how the security goes they may see some, all, or none of the records. So in the security check it will remove some of those resources from the software record. So my question is.... when I return my results list, is it a reference directly to the cache object? So when I remove a resource from the software object, it is really removing from cache as well? If that is the case, is there any way to not return it as a reference? Thanks!

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• How to create a progress bar while downloading a file using the windows API?

  - by Jorge Chayan

  i'm working on an application in MS Visual C++ using Windows API that must download a file and place it in a folder. I have already implemented the download using URLDownloadToFile function, but i want to create a PROGRESS_CLASS progress bar with marquee style while the file is being downloaded, but it doesn't seems to get animated in the process. This is the function I use for downloading: BOOL SOXDownload() { HRESULT hRez = URLDownloadToFile(NULL, "url","C:\\sox.zip", 0, NULL); if (hRez == E_OUTOFMEMORY ) { MessageBox(hWnd, "Out of memory Error","", MB_OK); return FALSE; } if (hRez != S_OK) { MessageBox(hWnd, "Error downloading sox.", "Error!", MB_ICONERROR | MB_SYSTEMMODAL); return FALSE; } if (hRez == S_OK) { BSTR file = SysAllocString(L"C:\\sox.zip"); BSTR folder = SysAllocString(L"C:\\"); Unzip2Folder(file, folder); ::MessageBoxA(hWnd, "Sox Binaries downloaded succesfully", "Success", MB_OK); } return TRUE; } Later I call inside WM_CREATE (in my main window's message processor): if (!fileExists("C:\\SOX\\SOX.exe")) { components[7] = CreateWindowEx(0, PROGRESS_CLASS, NULL, WS_VISIBLE | PBS_MARQUEE, GetSystemMetrics(SM_CXSCREEN) / 2 - 80, GetSystemMetrics(SM_CYSCREEN) / 2 + 25, 200, 50, hWnd, NULL, NULL, NULL); SetWindowText(components[7], "Downloading SoX"); SendMessage(components[7], PBM_SETRANGE, 0, (LPARAM) MAKELPARAM(0, 50)); SendMessage(components[7], PBM_SETMARQUEE, TRUE, MAKELPARAM( 0, 50)); SOXDownload(); SendMessage(components[7], WM_CLOSE, NULL, NULL); } And as I want, I get a tiny progress bar... But it's not animated, and when I place the cursor over the bar, the cursor indicates that the program is busy downloading the file. When the download is complete, the window closes as i requested: SendMessage(components[7], WM_CLOSE, NULL, NULL); So the question is how can I make the bar move while downloading the file? Considering that i want it done with marquee style for simplicity. Thanks in advance.

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• C++: inheritance problem

  - by Helltone

  It's quite hard to explain what I'm trying to do, I'll try: Imagine a base class A which contains some variables, and a set of classes deriving from A which all implement some method bool test() that operates on the variables inherited from A. class A { protected: int somevar; // ... }; class B : public A { public: bool test() { return (somevar == 42); } }; class C : public A { public: bool test() { return (somevar > 23); } }; // ... more classes deriving from A Now I have an instance of class A and I have set the value of somevar. int main(int, char* []) { A a; a.somevar = 42; Now, I need some kind of container that allows me to iterate over the elements i of this container, calling i::test() in the context of a... that is: std::vector<...> vec; // push B and C into vec, this is pseudo-code vec.push_back(&B); vec.push_back(&C); bool ret = true; for(i = vec.begin(); i != vec.end(); ++i) { // call B::test(), C::test(), setting *this to a ret &= ( a .* (&(*i)::test) )(); } return ret; } How can I do this? I've tried two methods: forcing a cast from B::* to A::*, adapting a pointer to call a method of a type on an object of a different type (works, but seems to be bad); using std::bind + the solution above, ugly hack; changing the signature of bool test() so that it takes an argument of type const A& instead of inheriting from A, I don't really like this solution because somevar must be public.

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• JSF: How to forward a request to another page in action?

  - by Satya

  I want to forward request to another page from action class I am using below code in my jsf action : public String submitUserResponse(){ ...... ...... parseResponse(uri,request,response); .... return "nextpage"; } public String parseResponse(String uri,request,response){ if(uri != null){ RequestDispatcher dispatcher = request.getRequestDispatcher(uri); dispatcher.forward(request, response); return null; } ................. .................. return "xxxx"; } "submitUserResponse" method is being called when user clicks the submit button from the jsp and this method returns "nextpage" string here request forwards to next page in normal flow. but in my requirement i will call "submitUserResponse () " which will execute and forwrd request to next page.It is going. but it is displaying some exceptions in server That is : java.lang.IllegalStateException: Cannot forward after response has been committed Here my doubts are: 1.why next lines of code is being executed after forwarding my request using dispatched.forward(uri) . Same thing happening in response.sendRedirect("").

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• How am i overriding this C++ inherited member function without the virtual keyword being used?

  - by Gary Willoughby

  I have a small program to demonstrate simple inheritance. I am defining a Dog class which is derived from Mammal. Both classes share a simple member function called ToString(). How is Dog overriding the implementation in the Mammal class, when i'm not using the virtual keyword? (Do i even need to use the virtual keyword to override member functions?) mammal.h #ifndef MAMMAL_H_INCLUDED #define MAMMAL_H_INCLUDED #include <string> class Mammal { public: std::string ToString(); }; #endif // MAMMAL_H_INCLUDED mammal.cpp #include <string> #include "mammal.h" std::string Mammal::ToString() { return "I am a Mammal!"; } dog.h #ifndef DOG_H_INCLUDED #define DOG_H_INCLUDED #include <string> #include "mammal.h" class Dog : public Mammal { public: std::string ToString(); }; #endif // DOG_H_INCLUDED dog.cpp #include <string> #include "dog.h" std::string Dog::ToString() { return "I am a Dog!"; } main.cpp #include <iostream> #include "dog.h" using namespace std; int main() { Dog d; std::cout << d.ToString() << std::endl; return 0; } output I am a Dog! I'm using MingW on Windows via Code::Blocks.

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• password-check directive in angularjs

  - by mpm

  I'm writing a password verify directive : Directives.directive("passwordVerify",function(){ return { require:"ngModel", link: function(scope,element,attrs,ctrl){ ctrl.$parsers.unshift(function(viewValue){ var origin = scope.$eval(attrs["passwordVerify"]); if(origin!==viewValue){ ctrl.$setValidity("passwordVerify",false); return undefined; }else{ ctrl.$setValidity("passwordVerify",true); return viewValue; } }); } }; }); html : <input data-ng-model='user.password' type="password" name='password' placeholder='password' required> <input data-ng-model='user.password_verify' type="password" name='confirm_password' placeholder='confirm password' required data-password-verify="user.password"> Given 2 password fields in a form, if both password values are equal then the field affected by the directive is valid. The issue is that it works one way (i.e. when I type a password in the password-verify field). However, when the original password field is updated, the password-verify doesn't become valid. Any idea how I could have a "two way binding verify?"

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• How to handle 30k files in a project which requires them?

  - by Jeremiah

  Visual Studio 2010 RC - Silverlight Application We have a library of images that we need to have access to. They are given to us from a vendor (through an installer) and they are not in a database, they are files in a folder (a very large monster of a folder). We do not control when the images change, so the vendor needs to be able to override them individually. We get updates frequently enough from this vendor to state that these images change "randomly" and without our (programmer) knowledge. The problem: I don't want 30K images in SVN. Heck, I don't even want to imagine them in my Solution. However, our application requires them in order to run properly. So, our build/staging servers need access to these images (we have two build servers). The Question: How would you handle it when your application will not work as specified without access to each of 30k images and you don't control when those images change? I'm do not want to have a crazy large SVN repository. Because I don't know when any of these images change, I really don't want them in my solution (definitely do not want a large solution, either). I also don't want a bunch of manual steps to do every time these images change. Our mantra, up to this point, has always been, any developer could download from SVN, compile and run our app. These images are going to kill that mantra. I'm tempted to make a WCF service that will return images if they exist and a dummy image if they don't. This way all dev boxes will return a dummy image and our build/staging/production boxes will return real images (ones that actually have the vendor's image installer installed on). This has to be a solved problem. What have other people done to handle these types of problems? I'm open to suggestions.

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• How do I want untill is finished in C#?

  - by Grienders

  Let's say, I want to send a request to a server and get a result from it: private static string Send(int id) { Task<HttpResponseMessage> responseTask = client.GetAsync("aaaaa"); string result = string.Empty; responseTask.ContinueWith(x => result = Print(x)); responseTask.Wait(); // it doesn't wait for complemeting of response task return result; } private static string Print(Task<HttpResponseMessage> httpTask) { Task<string> task = httpTask.Result.Content.ReadAsStringAsync(); string result = string.Empty; task.ContinueWith(t => { Console.WriteLine("Result: " + t.Result); result = t.Result; }); task.Wait(); // it does wait return result; } Am I using task correct? I don't think so because Send() method return string.Empty all the time, while Print returns the correct value. What am I doing wrong? How do I get a result from a server?

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• struct constructor + function parameter

  - by Oops

  Hi, I am a C++ beginner. I have the following code, the reult is not what I expect. The question is why, resp. what is wrong. For sure, the most of you see it at the first glance. struct Complex { float imag; float real; Complex( float i, float r) { imag = i; real = r; } Complex( float r) { Complex(0, r); } std::string str() { std::ostringstream s; s << "imag: " << imag << " | real: " << real << std::endl; return s.str(); } }; class Complexes { std::vector<Complex> * _complexes; public: Complexes(){ _complexes = new std::vector<Complex>; } void Add( Complex elem ) { _complexes->push_back( elem ); } std::string str( int index ) { std::ostringstream oss; Complex c = _complexes->at(index); oss << c.str(); return oss.str(); } }; int main(){ Complexes * cs = new Complexes(); //cs->Add(123.4f); cs->Add(Complex(123.4f)); std::cout << cs->str(0); return 0; } for now I am interested in the basics of c++ not in the complexnumber theory ;-) it would be nice if the "Add" function does also accept one real (without an extra overloading) instead of only a Complex-object is this possible? many thanks in advance Oops

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• Named captured substring in pcre++

  - by VDVLeon

  Hello, I want to capture named substring with the pcre++ library. I know the pcre library has the functionality for this, but pcre++ has not implemented this. This is was I have now (just a simple example): pcrepp::Pcre regex("test (?P<groupName>bla)"); if (regex.search("test bla")) { // Get matched group by name int pos = pcre_get_stringnumber( regex.get_pcre(), "groupName" ); if (pos == PCRE_ERROR_NOSUBSTRING) return; // Get match std::string temp = regex[pos - 1]; std::cout << "temp: " << temp << "\n"; } If I debug, pos return 1, and that is right, (?Pbla) is the 1th submatch (0 is the whole match). It should be ok. But... regex.matches() return 0. Why is that :S ? Btw. I do regex[pos - 1] because pcre++ reindexes the result with 0 pointing to the first submatch, so 1. So 1 becomes 0, 2 becomes 1, 3 becomes 2, etc. Does anybody know how to fix this?

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• How can I theme custom form(drupal 6.x)

  - by Andrew

  DRUPAL 6.X I have this custom form constructor inside my custom module which is invoke through ajax request. I’m attempting to theme this form with the template file reside in my theme directory. For that matter, I’ve registered my theme inside template.php file which reside in my theme folder. Here’s how this file looks – function my_theme() { return array( 'searchdb' => array( 'arguments' => array('form' => NULL), 'template' => 'searchform', ) ); } And the following is the excerpt of module code – function test_menu() { $my_form['searchdb'] = array( 'title' => 'Search db', 'page callback' => 'get_form', 'page arguments' => array(0), 'access arguments' => array('access content'), 'type' => MENU_CALLBACK, ); return $my_form; } function get_form($formtype){ switch($formtype){ case 'searchdb' : echo drupal_get_form('searchdb'); break; } } function searchdb(){ $form['customer_name'] = array( '#type' => 'textfield', '#title' => t('Customer Name'), '#size' => 50, '#attributes' => array('class' => 'name-textbox'), ); return $form; } As you can imagine, this is not working at all. Just to test if my theme is even registered, I’ve also tested with theme function but, it’s not called. I've checked template file name and form-id(through the outputted html source) and everything seems ok. I would be glad if anyone could point me to the right direction.

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• Merging ILists to bind on datagridview to avoid using a database view

  - by P.Bjorklund

  In the form we have this where IntaktsBudgetsType is a poorly named enum that only specifies wether to populate the datagridview after customer or product (You do the budgeting either after product or customer) private void UpdateGridView() { bs = new BindingSource(); bs.DataSource = intaktsbudget.GetDataSource(this.comboBoxKundID.Text, IntaktsBudgetsType.PerKund); dataGridViewIntaktPerKund.DataSource = bs; } This populates the datagridview with a database view that merge the product, budget and customer tables. The logic has the following method to get the correct set of IList from the repository which only does GetTable<T>.ToList<T> public IEnumerable<IntaktsBudgetView> GetDataSource(string id, IntaktsBudgetsType type) { IList<IntaktsBudgetView> list = repository.SelectTable<IntaktsBudgetView>(); switch (type) { case IntaktsBudgetsType.PerKund: return from i in list where i.kundId == id select i; case IntaktsBudgetsType.PerProdukt: return from i in list where i.produktId == id select i; } return null; } Now I don't want to use a database view since that is read-only and I want to be able to perform CRUD actions on the datagridview. I could build a class that acts as a wrapper for the whole thing and bind the different table values to class properties but that doesn't seem quite right since I would have to do this for every single thing that requires "the merge". Something pretty important (and probably basic) is missing the the thought process but after spending a weekend on google and in books I give up and turn to the SO community.

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• How to lazy load a data structure (python)

  - by Anton Geraschenko

  I have some way of building a data structure (out of some file contents, say): def loadfile(FILE): return # some data structure created from the contents of FILE So I can do things like puppies = loadfile("puppies.csv") # wait for loadfile to work kitties = loadfile("kitties.csv") # wait some more print len(puppies) print puppies[32] In the above example, I wasted a bunch of time actually reading kitties.csv and creating a data structure that I never used. I'd like to avoid that waste without constantly checking if not kitties whenever I want to do something. I'd like to be able to do puppies = lazyload("puppies.csv") # instant kitties = lazyload("kitties.csv") # instant print len(puppies) # wait for loadfile print puppies[32] So if I don't ever try to do anything with kitties, loadfile("kitties.csv") never gets called. Is there some standard way to do this? After playing around with it for a bit, I produced the following solution, which appears to work correctly and is quite brief. Are there some alternatives? Are there drawbacks to using this approach that I should keep in mind? class lazyload: def __init__(self,FILE): self.FILE = FILE self.F = None def __getattr__(self,name): if not self.F: print "loading %s" % self.FILE self.F = loadfile(self.FILE) return object.__getattribute__(self.F, name) What might be even better is if something like this worked: class lazyload: def __init__(self,FILE): self.FILE = FILE def __getattr__(self,name): self = loadfile(self.FILE) # this never gets called again # since self is no longer a # lazyload instance return object.__getattribute__(self, name) But this doesn't work because self is local. It actually ends up calling loadfile every time you do anything.

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• Accessing derived class members with a base class pointer

  - by LRB

  I am making a simple console game in C++ I would like to know if I can access members from the 'entPlayer' class while using a pointer that is pointing to the base class ( 'Entity' ): class Entity { public: void setId(int id) { Id = id; } int getId() { return Id; } protected: int Id; }; class entPlayer : public Entity { string Name; public: entPlayer() { Name = ""; Id = 0; } void setName(string name) { Name = name; } string getName() { return Name; } }; Entity *createEntity(string Type) { Entity *Ent = NULL; if (Type == "player") { Ent = new entPlayer; } return Ent; } void main() { Entity *ply = createEntity("player"); ply->setName("Test"); ply->setId(1); cout << ply->getName() << endl; cout << ply->getId() << endl; delete ply; } How would I be able to call ply-setName etc? OR If it's not possible that way, what would be a better way?

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• Python lists/arrays: disable negative indexing wrap-around

  - by wim

  While I find the negative number wraparound (i.e. A[-2] indexing the second-to-last element) extremely useful in many cases, there are often use cases I come across where it is more of an annoyance than helpful, and I find myself wishing for an alternate syntax to use when I would rather disable that particular behaviour. Here is a canned 2D example below, but I have had the same peeve a few times with other data structures and in other numbers of dimensions. import numpy as np A = np.random.randint(0, 2, (5, 10)) def foo(i, j, r=2): '''sum of neighbours within r steps of A[i,j]''' return A[i-r:i+r+1, j-r:j+r+1].sum() In the slice above I would rather that any negative number to the slice would be treated the same as None is, rather than wrapping to the other end of the array. Because of the wrapping, the otherwise nice implementation above gives incorrect results at boundary conditions and requires some sort of patch like: def ugly_foo(i, j, r=2): def thing(n): return None if n < 0 else n return A[thing(i-r):i+r+1, thing(j-r):j+r+1].sum() I have also tried zero-padding the array or list, but it is still inelegant (requires adjusting the lookup locations indices accordingly) and inefficient (requires copying the array). Am I missing some standard trick or elegant solution for slicing like this? I noticed that python and numpy already handle the case where you specify too large a number nicely - that is, if the index is greater than the shape of the array it behaves the same as if it were None.

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• a basic issue in implementing validations through properties ? Please guide me.

  - by haansi

  hello, thanks for your attention and time. I want to implement validations in settter of properties. Here is an issue where your expert help is required please. I have idea of how I will do validations before setting value. but not getting what to do if passed value is not correct. Just not setting is not a acceptable solution as I want to return an appropriate message to user (in a label in web form). My example code is: private int id; public int Id { get { return id; } set { bool result = IsNumber(value); if (result==false) { // What to do if passed data is not valid ? how to give a appropriate message to user that what is wrong ? } id = value; } } A thought was to use return but it is not allowed. Throwing error looks not good as generally we avoid thorwing custom errors. Please guide and help me. thanks in anticipation haansi

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• jQuery innerHTML does not work properly (!)

  - by Kayes

  I was trying to build an <a> tag and set it in a <td> of a table. The string is built perfectly but when I set this as the innerHTML using jQuery, the string gets broken. I can't figure out why this is happening? Any clues? Here's the string I want to set in the <td>: <a onclick='return EditIssueItemBatch('1c1e27a2-beac-4772-a26f-6a7e05529a65', '498ba483-ca06-4b23-b3a9-0085e4760ff1')'>Edit</a> But here is how it looks after setting as innerHTML: <A onclick="return EditIssueItemBatch(" ?498ba483-ca06-4b23-b3a9-0085e4760ff1?)? 1c1e27a2-beac-4772-a26f-6a7e05529a65?,>Edit</A> And the following is my code-snippet.. var tr = $("#itemIssueBatchListTable > tbody:last").children()[data.Index + 1]; ... ... var strBuff = []; strBuff.push("<a onclick='return EditIssueItemBatch('"); strBuff.push(data.ItemIssueBatch.ItemCode_FK); strBuff.push("', '"); strBuff.push(data.ItemIssueBatch.StockDetCode_FK); strBuff.push("')'>Edit</a>"); tr.cells[9].innerHTML = strBuff.join(""); ... ...

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• Scala always returning true....WHY?

  - by jhamm

  I am trying to learn Scala and am a newbie. I know that this is not optimal functional code and welcome any advice that anyone can give me, but I want to understand why I keep getting true for this function. def balance(chars: List[Char]): Boolean = { val newList = chars.filter(x => x.equals('(') || x.equals(')')); return countParams(newList, 0) } def countParams(xs: List[Char], y: Int): Boolean = { println(y + " right Here") if (y < 0) { println(y + " Here") return false } else { println(y + " Greater than 0") if (xs.size > 0) { println(xs.size + " this is the size") xs match { case xs if (xs.head.equals('(')) => countParams(xs.tail, y + 1) case xs if (xs.head.equals(')')) => countParams(xs.tail, y - 1) case xs => 0 } } } return true; } balance("()())))".toList) I know that I am hitting the false branch of my if statement, but it still returns true at the end of my function. Please help me understand. Thanks.

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• Extending a form field to add new validations.

  - by duallain

  I've written an app that uses forms to collect information that is then sent in an email. Many of these forms have a filefield used to attach files to the email. I'd like to validate two things, the size of the file (to ensure the emails are accepted by our mail server. I'd also like to check the file extension, to discourage attaching file types not useable for our users. (This is the python class I'm trying to extend) class FileField(Field): widget = FileInput default_error_messages = { 'invalid': _(u"No file was submitted. Check the encoding type on the form."), 'missing': _(u"No file was submitted."), 'empty': _(u"The submitted file is empty."), 'max_length': _(u'Ensure this filename has at most %(max)d characters (it has %(length)d).'), } def __init__(self, *args, **kwargs): self.max_length = kwargs.pop('max_length', None) super(FileField, self).__init__(*args, **kwargs) def clean(self, data, initial=None): super(FileField, self).clean(initial or data) if not self.required and data in EMPTY_VALUES: return None elif not data and initial: return initial # UploadedFile objects should have name and size attributes. try: file_name = data.name file_size = data.size except AttributeError: raise ValidationError(self.error_messages['invalid']) if self.max_length is not None and len(file_name) > self.max_length: error_values = {'max': self.max_length, 'length': len(file_name)} raise ValidationError(self.error_messages['max_length'] % error_values) if not file_name: raise ValidationError(self.error_messages['invalid']) if not file_size: raise ValidationError(self.error_messages['empty']) return data

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• What's wrong with output parameters?

  - by Chris McCall

  Both in SQL and C#, I've never really liked output parameters. I never passed parameters ByRef in VB6, either. Something about counting on side effects to get something done just bothers me. I know they're a way around not being able to return multiple results from a function, but a rowset in SQL or a complex datatype in C# and VB work just as well, and seem more self-documenting to me. Is there something wrong with my thinking, or are there resources from authoritative sources that back me up? What's your personal take on this and why? What can I say to colleagues that want to design with output parameters that might convince them to use different structures? EDIT: interesting turn- the output parameter I was asking this question about was used in place of a return value. When the return value is "ERROR", the caller is supposed to handle it as an exception. I was doing that but not pleased with the idea. A coworker wasn't informed of the need to handle this condition and as a result, a great deal of money was lost as the procedure failed silently!

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• C++, using one byte to store two variables

  - by 2di

  Hi All I am working on representation of the chess board, and I am planning to store it in 32 bytes array, where each byte will be used to store two pieces. (That way only 4 bits are needed per piece) Doing it in that way, results in a overhead for accessing particular index of the board. Do you think that, this code can be optimised or completely different method of accessing indexes can be used? c++ char getPosition(unsigned char* c, int index){ //moving pointer c+=(index>>1); //odd number if (index & 1){ //taking right part return *c & 0xF; }else { //taking left part return *c>>4; } } void setValue(unsigned char* board, char value, int index){ //moving pointer board+=(index>>1); //odd number if (index & 1){ //replace right part //save left value only 4 bits *board = (*board & 0xF0) + value; }else { //replacing left part *board = (*board & 0xF) + (value<<4); } } int main() { char* c = (char*)malloc(32); for (int i = 0; i < 64 ; i++){ setValue((unsigned char*)c, i % 8,i); } for (int i = 0; i < 64 ; i++){ cout<<(int)getPosition((unsigned char*)c, i)<<" "; if (((i+1) % 8 == 0) && (i > 0)){ cout<<endl; } } return 0; } I am equally interested in your opinions regarding chess representations, and optimisation of the method above, as a stand alone problem. Thanks a lot

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• Determing if an unordered vector<T> has all unique elements

  - by Hooked

  Profiling my cpu-bound code has suggested I that spend a long time checking to see if a container contains completely unique elements. Assuming that I have some large container of unsorted elements (with < and = defined), I have two ideas on how this might be done: The first using a set: template <class T> bool is_unique(vector<T> X) { set<T> Y(X.begin(), X.end()); return X.size() == Y.size(); } The second looping over the elements: template <class T> bool is_unique2(vector<T> X) { typename vector<T>::iterator i,j; for(i=X.begin();i!=X.end();++i) { for(j=i+1;j!=X.end();++j) { if(*i == *j) return 0; } } return 1; } I've tested them the best I can, and from what I can gather from reading the documentation about STL, the answer is (as usual), it depends. I think that in the first case, if all the elements are unique it is very quick, but if there is a large degeneracy the operation seems to take O(N^2) time. For the nested iterator approach the opposite seems to be true, it is lighting fast if X[0]==X[1] but takes (understandably) O(N^2) time if all the elements are unique. Is there a better way to do this, perhaps a STL algorithm built for this very purpose? If not, are there any suggestions eek out a bit more efficiency?

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• Strange compiler complaint when using similar code

  - by Jason

  For a project, I have to ask the user for a file name, and I'm reading it in character by character using getchar. From the main, I call the function char *coursename= introPrint(); //start off to print the usage directions and get the first bit of input. That function is defined as char *introPrint(){ int size= 20; int c; int length=0; char buffer[size]; //instructions printout, cut for brevity //get coursename from user and return it while ( (c=getchar()) != EOF && (c != '\n') ){ buffer[length++]= c; if (length==size-1) break; } buffer[length]=0; return buffer; } This is basically identical code I wrote to ask the user for input, replace the character echo with asterisks, then print out the results. Here, though, I'm getting a function returns address of local variable warning for the return statement. So why am I getting no warnings from the other program, but trigger one for this code?

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