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• How to organize and manage multiple database credentials in application?

  - by Polaris878

  Okay, so I'm designing a stand-alone web service (using RestLET as my framework). My application is divided in to 3 layers: Data Layer (just above the database, provides APIs for connecting to/querying database, and a database object) Object layer (responsible for serialization from the data layer... provides objects which the client layer can use without worrying about database) Client layer (This layer is the RestLET web service... basically just creates objects from the object layer and fulfills webservice request) Now, for each object I create in the object layer, I want to use different credentials (so I can sandbox each object...). The object layer should not know the exact credentials (IE the login/pw/DB URL etc). What would be the best way to manage this? I'm thinking that I should have a super class Database object in my data layer... and each subclass will contain the required log-in information... this way my object layer can just go Database db = new SubDatabase(); and then continue using that database. On the client level, they would just be able to go ItemCollection items = new ItemCollection(); and have no idea/control over the database that gets connected. I'm asking this because I am trying to make my platform extensible, so that others can easily create services off of my platform. If anyone has any experience with these architectural problems or how to manage this sort of thing I'd appreciate any insight or advice... Feel free to ask questions if this is confusing. Thanks! My platform is Java, the REST framework I'm using is RestLET, my database is MySQL.

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• Returning XML natively in a .NET (C#) webservice?

  - by James McMahon

  I realize that SOAP webservices in .NET return XML representation of whatever object the web method returns, but if I want to return data formatting in XML what is the best object to store it in? I am using the answer to this question to write my XML, here is the code: XmlWriter writer = XmlWriter.Create(pathToOutput); writer.WriteStartDocument(); writer.WriteStartElement("People"); writer.WriteStartElement("Person"); writer.WriteAttributeString("Name", "Nick"); writer.WriteEndElement(); writer.WriteStartElement("Person"); writer.WriteStartAttribute("Name"); writer.WriteValue("Nick"); writer.WriteEndAttribute(); writer.WriteEndElement(); writer.WriteEndElement(); writer.WriteEndDocument(); writer.Flush(); Now I can return this output as a String to my calling webmethod, but it shows up as <string> XML HERE </string>, is there anyway to just return the full xml? Please in your answer, give an example of how to use said object with either XmlWriter or another internal object (if you consider XmlWriter to be a poor choice). The System.Xml package (namespace) has many objects, but I haven't been able to uncover decent documentation on how to use the objects together, or what to use for what situations.

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• Saving animated GIFs using urllib.urlopen (image saved does not animate)

  - by wenbert

  I have Apache2 + Django + X-sendfile. My problem is that when I upload an animated GIF, it won't "animate" when I output through the browser. Here is my code to display the image located outside the public accessible directory. def raw(request,uuid): target = str(uuid).split('.')[:-1][0] image = Uploads.objects.get(uuid=target) path = image.path filepath = os.path.join(path,"%s.%s" % (image.uuid,image.ext)) response = HttpResponse(mimetype=mimetypes.guess_type(filepath)) response['Content-Disposition']='filename="%s"'\ %smart_str(image.filename) response["X-Sendfile"] = filepath response['Content-length'] = os.stat(filepath).st_size return response UPDATE It turns out that it works. My problem is when I try to upload an image via URL. It probably doesn't save the entire GIF? def handle_url_file(request): """ Open a file from a URL. Split the file to get the filename and extension. Generate a random uuid using rand1() Then save the file. Return the UUID when successful. """ try: file = urllib.urlopen(request.POST['url']) randname = rand1(settings.RANDOM_ID_LENGTH) newfilename = request.POST['url'].split('/')[-1] ext = str(newfilename.split('.')[-1]).lower() im = cStringIO.StringIO(file.read()) # constructs a StringIO holding the image img = Image.open(im) filehash = checkhash(im) image = Uploads.objects.get(filehash=filehash) uuid = image.uuid return "%s" % (uuid) except Uploads.DoesNotExist: img.save(os.path.join(settings.UPLOAD_DIRECTORY,(("%s.%s")%(randname,ext)))) del img filesize = os.stat(os.path.join(settings.UPLOAD_DIRECTORY,(("%s.%s")%(randname,ext)))).st_size upload = Uploads( ip = request.META['REMOTE_ADDR'], filename = newfilename, uuid = randname, ext = ext, path = settings.UPLOAD_DIRECTORY, views = 1, bandwidth = filesize, source = request.POST['url'], size = filesize, filehash = filehash, ) upload.save() #return uuid return "%s" % (upload.uuid) except IOError, e: raise e Any ideas? Thanks! Wenbert

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• Right way to return proxy model instance from a base model instance in Django ?

  - by sotangochips

  Say I have models: class Animal(models.Model): type = models.CharField(max_length=255) class Dog(Animal): def make_sound(self): print "Woof!" class Meta: proxy = True class Cat(Animal): def make_sound(self): print "Meow!" class Meta: proxy = True Let's say I want to do: animals = Animal.objects.all() for animal in animals: animal.make_sound() I want to get back a series of Woofs and Meows. Clearly, I could just define a make_sound in the original model that forks based on animal_type, but then every time I add a new animal type (imagine they're in different apps), I'd have to go in and edit that make_sound function. I'd rather just define proxy models and have them define the behavior themselves. From what I can tell, there's no way of returning mixed Cat or Dog instances, but I figured maybe I could define a "get_proxy_model" method on the main class that returns a cat or a dog model. Surely you could do this, and pass something like the primary key and then just do Cat.objects.get(pk = passed_in_primary_key). But that'd mean doing an extra query for data you already have which seems redundant. Is there any way to turn an animal into a cat or a dog instance in an efficient way? What's the right way to do what I want to achieve?

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• Duplicate Symbol Linker Error (C++ help)

  - by Vash265

  Hi. I'm learning some CSP (constraint satisfaction) theory stuff right now, and am using this library to parse XML files. I'm using Xcode as an IDE. My program compiles fine, but when it goes to link the files, I get a duplicate symbol error with the XMLParser_libxml2.hh file. My files are separated as such: A class header file that includes the XMLParser file above A class implementation file that include the class header file A main file that includes the class header file The duplicate symbol is occurring in main.o and classfile.o, but as far as I can tell, I'm not actually adding that .hh file twice. Full error: ld: duplicate symbol bool CSPXMLParser::UTF8String::to<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >(std::basic_string<char, std::char_traits<char>, std::allocator<char> >&) constin /Users/vash265/CSP/Untitled/build/Untitled.build/Debug/Untitled.build/Objects-normal/x86_64/dStructFill.o and /Users/vash265/CSP/Untitled/build/Untitled.build/Debug/Untitled.build/Objects-normal/x86_64/main.o Copying the implementation of the class into the main file and taking the class implementation file out of the compilation target alleviates the error, but it's a disorganized mess this way, and I'll be adding more classes very soon (and it would be nice to have them in separate files). As I've come to understand it, this is caused by the file (XMLParser_libxml2.hh) having both the class and function definition and implementation in one file (and it seems as though this might have been necessary due to the use of templates in that 'header' file). Any ideas on how to get around sticking all my class files in my main.cpp? (I've tried ifdefs, they don't work).

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• Django: Determining if a user has voted or not

  - by TheLizardKing

  I have a long list of links that I spit out using the below code, total votes, submitted by, the usual stuff but I am not 100% on how to determine if the currently logged in user has voted on a link or not. I know how to do this from within my view but do I need to alter my below view code or can I make use of the way templates work to determine it? I have read http://stackoverflow.com/questions/1528583/django-vote-up-down-method but I don't quite understand what's going on ( and don't need any ofjavascriptery). Models (snippet): class Link(models.Model): category = models.ForeignKey(Category, blank=False, default=1) user = models.ForeignKey(User) created = models.DateTimeField(auto_now_add=True) modified = models.DateTimeField(auto_now=True) url = models.URLField(max_length=1024, unique=True, verify_exists=True) name = models.CharField(max_length=512) def __unicode__(self): return u'%s (%s)' % (self.name, self.url) class Vote(models.Model): link = models.ForeignKey(Link) user = models.ForeignKey(User) created = models.DateTimeField(auto_now_add=True) def __unicode__(self): return u'%s vote for %s' % (self.user, self.link) Views (snippet): def hot(request): links = Link.objects.select_related().annotate(votes=Count('vote')).order_by('-created') for link in links: delta_in_hours = (int(datetime.now().strftime("%s")) - int(link.created.strftime("%s"))) / 3600 link.popularity = ((link.votes - 1) / (delta_in_hours + 2)**1.5) if request.user.is_authenticated(): try: link.voted = Vote.objects.get(link=link, user=request.user) except Vote.DoesNotExist: link.voted = None links = sorted(links, key=lambda x: x.popularity, reverse=True) links = paginate(request, links, 15) return direct_to_template( request, template = 'links/link_list.html', extra_context = { 'links': links, }) The above view actually accomplishes what I need but in what I believe to be a horribly inefficient way. This causes the dreaded n+1 queries, as it stands that's 33 queries for a page containing just 29 links while originally I got away with just 4 queries. I would really prefer to do this using Django's ORM or at least .extra(). Any advice?

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• Implementing list position locator in C++?

  - by jfrazier

  I am writing a basic Graph API in C++ (I know libraries already exist, but I am doing it for the practice/experience). The structure is basically that of an adjacency list representation. So there are Vertex objects and Edge objects, and the Graph class contains: list<Vertex *> vertexList list<Edge *> edgeList Each Edge object has two Vertex* members representing its endpoints, and each Vertex object has a list of Edge* members representing the edges incident to the Vertex. All this is quite standard, but here is my problem. I want to be able to implement deletion of Edges and Vertices in constant time, so for example each Vertex object should have a Locator member that points to the position of its Vertex* in the vertexList. The way I first implemented this was by saving a list::iterator, as follows: vertexList.push_back(v); v->locator = --vertexList.end(); Then if I need to delete this vertex later, then rather than searching the whole vertexList for its pointer, I can call: vertexList.erase(v->locator); This works fine at first, but it seems that if enough changes (deletions) are made to the list, the iterators will become out-of-date and I get all sorts of iterator errors at runtime. This seems strange for a linked list, because it doesn't seem like you should ever need to re-allocate the remaining members of the list after deletions, but maybe the STL does this to optimize by keeping memory somewhat contiguous? In any case, I would appreciate it if anyone has any insight as to why this happens. Is there a standard way in C++ to implement a locator that will keep track of an element's position in a list without becoming obsolete? Much thanks, Jeff

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• Fast sketching tools for drawing C/C++ structs, pointers, etc...

  - by tomasorti

  Hi. I would like to know what do you use to sketch relations between different entities in C/C++. This can be a very broad issue, so I'll try to clarify a bit more my question and give an example. I'm looking for something that is simple enough as a user, and let me sketch easily containers, pointers, etc... in an informal way. The aim is to document some structs relations to pass them to junior developers. A look at the drawings is supposed to accelerate the understanding of the code. My solutions at this moment are to use: 1) Paper & pencil. 2) Microsoft PowerPoint/Word Autoshapes. 3) Freeware Dia. Other ones could be: 4) Microsoft Visio, but my company does not own licenses. 5) UML tools. I don't want to go this way. This is what I mean a more formal solution. I know tools like Rational Rose are great, and I tried boUML and violet and they are fine in some parts, but I prefer the flexibility of options 2) or 3). Finally, let me write down a more concrete example: Let's say I what to sketch a map that contains another map as the mapped value, and that one contains a struct as the mapped value, that holds a vector of pointers of a type and a pointer to other type. Also, there exist other structs that hold pointers to the objects pointed by the previous map, so there are objects pointed from different places. This is just one example I have, but you can easily come with one from you experience. What would you use to sketch this example or another similar you have dealt with? Best regards, Tomas.

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• How can i iterate through QListWidget items and work with each item?

  - by Hossein

  In CSharp its as simple as writting : listBox1.Items.Add("Hello"); listBox1.Items.Add("There"); foreach (string item in listBox1.Items ) { MessageBox.Show(item.ToString()); } and i can easily add different objects to a list box and then retrieve them using foreach. I tried the same approach in Qt 4.8.2 but it seems they are different.though they look very similar at first.I found that Qt supports foreach so i went on and tried something like : foreach(QListWidgetItem& item,ui->listWidget->items()) { item.setTextColor(QColor::blue()); } which failed clearly.It says the items() needs a parameter which confuses me.I am trying to iterate through the ListBox itself, so what does this mean? I tried passing the ListBox object as the parameter itself this again failed too: foreach(QListWidgetItem& item,ui->listWidget->items(ui->listWidget)) { item.setTextColor(QColor::blue()); } So here are my questions: How can I iterate through a QListWidget items in Qt? Can i store objects as items in QListWidgets like C#? How can i convert an object in QListWidgets to string(C#s ToString counter part in Qt) ? (suppose i want to use a QMessagBox instead of that setTextColor and want to print out all string items in the QlistWidget.)

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• Deserialize json with json.net c#

  - by 76mel

  Hi, am new to Json so a little green. I have a Rest Based Service that returns a json string; {"treeNode":[{"id":"U-2905","pid":"R","userId":"2905"}, {"id":"U-2905","pid":"R","userId":"2905"}]} I have been playing with the Json.net and trying to Deserialize the string into Objects etc. I wrote an extention method to help. public static T DeserializeFromJSON<T>(this Stream jsonStream, Type objectType) { T result; using (StreamReader reader = new StreamReader(jsonStream)) { JsonSerializer serializer = new JsonSerializer(); try { result = (T)serializer.Deserialize(reader, objectType); } catch (Exception e) { throw; } } return result; } I was expecting an array of treeNode[] objects. But its seems that I can only deserialize correctly if treeNode[] property of another object. public class treeNode { public string id { get; set; } public string pid { get; set; } public string userId { get; set; } } I there a way to to just get an straight array from the deserialization ? Cheers

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• Static Variables somehow maintaining state?

  - by gfoley

  I am working on an existing project, setup by another coder. I'm having some trouble understanding how state is being maintained between pages. There is a Class library which has some helper objects. Mostly these objects are just used for there static methods and rarely instantiated or inherited. This is an example class I'm testing with. public sealed class Application { public static string Test; } Now when i run something like the following in the base class of my page, I would expect the result to be "1: 2:Test" all the time (note that "1" is empty), but strangly its only this way the first time it is run. Then every time afterwards its "1:Test 2:Test". Somehow its maintaining the state of the static variable between pages and being refreshed?? Response.Write("1:" + SharedLibrary.Application.Test); SharedLibrary.Application.Test = "Test"; Response.Write(" 2:" + SharedLibrary.Application.Test); I need to create more classes like this, but want to understand why this is occurring in the first place. Many Thanks

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• Style first 2 TextViews in Android ListView differently

  - by Kurtis Nusbaum

  I have a ListView and I want the first two entries in it to be displayed differently than the rest. Nothing fancy, I want them all to just be text views. But the first two entries need to have different sizes and weights than the rest. I tried modifying the ArrayAdapter class like so: private class BusStopAdapter<T> extends ArrayAdapter<T>{ public BusStopAdapter( Context context, int textViewResourceId, List<T> objects) { super(context, textViewResourceId, objects); } public View getView(int position, View convertView, ViewGroup parent) { TextView toReturn = (TextView)super.getView(position, convertView, parent); if(position == 0){ toReturn.setTextSize(12); toReturn.setText("Previous Bus: " + toReturn.getText()); toReturn.setPadding(0,0,0,0); } else if(position == 1){ toReturn.setTextSize(20); toReturn.setPadding( toReturn.getPaddingLeft(), 0, toReturn.getPaddingRight(), 0 ); toReturn.setText("Next Bus: " + toReturn.getText()); toReturn.setGravity(Gravity.CENTER_HORIZONTAL|Gravity.TOP); } return toReturn; } } But this inadvertantly causes some of the other textviews to take on these special attributes. I think it's because cause textviews get "recycled" in the AbsListAdapter class.

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• Windows 7 versus Windows XP multithreading - Delphi app not acting right

  - by Robert Oschler

  I'm having a problem with a Delphi Pro 6 application that I wrote on my Windows XP machine when it runs on Windows 7. I don't have Windows 7 to test yet and I'm trying to see if Windows 7 might be the source of the trouble. Is there a fundamental difference between the way Windows 7 handles threads compared to Windows XP? I am seeing things happen out of sequence in my error logs on Windows 7 and it's causing problems. For example, objects that should have been initialized are uninitialized when running on Windows 7, yet those objects are initialized on Windows XP by the time they are needed. Some questions: 1) Are there any core differences that could cause threads/processes to behave differently between the two operating system versions? 2) I know this next question may seem absurd, but does Windows 7 attempt to split/fork threads that aren't split/forked on Windows XP? 3) And lastly, are there any known issues with FPU handling that can cause XP programs trouble when run on Windows 7 due to operational differences in wait state handling or register storage, or perhaps something like Exception mask settings, etc? 4) Any 32-bit versus 64-bit issues that could be creating trouble here? -- roschler

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• Optimizing a bin-placement algorithm

  - by user258651

  Alright, I've got two collections, and I need to place elements from collection1 into the bins (elements) of collection2, based on whether their value falls within a given bin's range. For a concrete example, assume I have a sorted collection objects (bins) which have an int range ([1...4], [5..10], etc). I need to determine the range an int falls in, and place it in the appropriate bin. foreach(element n in collection1) { foreach(bin m in collection2) { if (m.inRange(n)) { m.add(n); break; } } } So the obvious NxM complexity algorithm is there, but I really would like to see Nxlog(M). To do this I'd like to use BinarySearch in place of the inner foreach loop. To use BinarySearch, I need to implement an IComparer class to do the searching for me. The problem I'm running into is this approach would require me to make an IComparer.Compare function that compares two different types of objects (an element to its bin), and that doesn't seem possible or correct. So I'm asking, how should I write this algorithm?

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• C++ Builder 2010 Exception Dead Lock ???

  - by James

  Hello Is this some kind of exception dead lock i am facing? How to avoid it ? Have a look at below line where i have TIdContext objects of connected clients stored in an objlist and at times i need to process it. But if one user is disconnected while another thread is processing the list, then for that freed TIdContext-Data object I am getting Access voilation, Ok its fine i am using try/catch but problem is that at below line there is some kind of dead lock and process hangs , if i attach a debuger it show Access voilation Again and Again and Again, and cpu coonsumption goes up because of that exception dead lock. AnsiString UserID = ((Tmyobject*) ((TIdContext*) ObjList->Objects[i])->Data)->UserID; i know i can check before accessing the object, if object is not Null, It works.. But my question is what if once in a blue moon the Data object is freed at the point when NULL check is performed and on next line when again i am accessing the object i get same dead lock ??? So how to avoid/handle this dead lock exception ? Here is the call stack... :005F07C0 System::AnsiStringBase::AnsiStringBase(this=:0285FCE0, src=????) :0040223F System::AnsiStringT<0>::AnsiStringT<0>(this=:0285FCE0, src=:00000008) :00457996 TSomeClass::SomeFunction(this=:009D8230, UserID={ }, DataSize={ }, ) :0047BFF1 __linkproc__ ThreadProc(Thread=:009561C0) :004AD00E __linkproc__ ThreadWrapper(Parameter=:009EAA30) :7c80b729 ; C:\WINDOWS\system32\kernel32.dll Please helppppppppppppppppppppp Thanks

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• How to provide an inline model field with a queryset choices without losing field value for inline r

  - by Judith Boonstra

  The code displayed below is providing the choices I need for the app field, and the choices I need for the attr field when using Admin. I am having a problem with the attr field on the inline form for already saved records. The attr selected for these saved does show in small print above the field, but not within the field itself. # MODELS: Class Vocab(models.Model): entity = models.Charfield, max_length = 40, unique = True) Class App(models.Model): name = models.ForeignKey(Vocab, related_name = 'vocab_appname', unique = True) app = SelfForeignKey('self, verbose_name = 'parent', blank = True, null = True) attr = models.ManyToManyField(Vocab, related_name = 'vocab_appattr', through ='AppAttr' def parqs(self): a method that provides a queryset consisting of available apps from vocab, excluding self and any apps within the current app's dependent line. def attrqs(self): a method that provides a queryset consisting of available attr from vocab excluding those already selected by current app, 2) those already selected by any apps within the current app's parent line, and 3) those selected by any apps within the current app's dependent line. Class AppAttr(models.Model): app = models.ForeignKey(App) attr = models.ForeignKey(Vocab) # FORMS: from models import AppAttr def appattr_form_callback(instance, field, *args, **kwargs) if field.name = 'attr': if instance: return field.formfield(queryset = instance.attrqs(), *kwargs) return field.formfield(*kwargs) # ADMIN: necessary imports class AppAttrInline(admin.TabularInline): model = AppAttr def get_formset(self, request, obj = None, **kwargs): kwargs['formfield_callback'] = curry(appattr_form_callback, obj) return super(AppAttrInline, self).get_formset(request, obj, **kwargs) class AppForm(forms.ModelForm): class Meta: model = App def __init__(self, *args, **kwargs): super(AppForm, self).__init__(*args, **kwargs) if self.instance.id is None: working = App.objects.all() else: thisrec = App.objects.get(id = self.instance.id) working = thisrec.parqs() self.fields['par'].queryset = working class AppAdmin(admin.ModelAdmin): form = AppForm inlines = [AppAttrInline,] fieldsets = .......... necessary register statements

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• "no inclosing instance error " while getting top term frequencies for document from Lucene index

  - by Julia

  Hello ! I am trying to get the most occurring term frequencies for every particular document in Lucene index. I am trying to set the treshold of top occuring terms that I care about, maybe 20 However, I am getting the "no inclosing instance of type DisplayTermVectors is accessible" when calling Comparator... So to this function I pass vector of every document and max top terms i would like to know protected static Collection getTopTerms(TermFreqVector tfv, int maxTerms){ String[] terms = tfv.getTerms(); int[] tFreqs = tfv.getTermFrequencies(); List result = new ArrayList(terms.length); for (int i = 0; i < tFreqs.length; i++) { TermFrq tf = new TermFrq(terms[i], tFreqs[i]); result.add(tf); } Collections.sort(result, new FreqComparator()); if(maxTerms < result.size()){ result = result.subList(0, maxTerms); } return result; } /Class for objects to hold the term/freq pairs/ static class TermFrq{ private String term; private int freq; public TermFrq(String term,int freq){ this.term = term; this.freq = freq; } public String getTerm(){ return this.term; } public int getFreq(){ return this.freq; } } /*Comparator to compare the objects by the frequency*/ class FreqComparator implements Comparator{ public int compare(Object pair1, Object pair2){ int f1 = ((TermFrq)pair1).getFreq(); int f2 = ((TermFrq)pair2).getFreq(); if(f1 > f2) return 1; else if(f1 < f2) return -1; else return 0; } } Explanations and corrections i will very much appreciate, and also if someone else had experience with term frequency extraction and did it better way, I am opened to all suggestions! Please help!!!! Thanx!

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• Animate and form rows, arrays, AS3

  - by VideoDnd

  Question How can I animate and form rows together? Explanation One 'for loop' is for animation, the other 'for loop' is for making rows. I want to understand how to use arrays and create a row of sprite animations. 'for loop' for animation //FRAMES ARRAY //THIS SETS UP MY ANIMATION FOR TIMER EVENT var frames:Array = [ new Frame1(), new Frame2(), new Frame3(), new Frame4(), new Frame5(), new Frame6(), new Frame7(), new Frame8(), new Frame9(), new Frame0(), ]; for each (var frame:Sprite in frames) { addChild(frame); } 'for loop' for rows //THIS MAKES A ROW OF DISPLAY OBJECTS var numberOfClips:Number = 11; var xStart:Number = 0; var yStart:Number = 0; var xVal:Number = xStart; var xOffset:Number = 2; for (var $:Number=0; $<numberOfClips; $++) { //DUDE ARRAY var dude:Array = frames; dude.y = yStart +11; dude.x = xVal +55; xVal = dude.x + dude.width + this.xOffset; } timer var timer:Timer = new Timer(100); timer.addEventListener(TimerEvent.TIMER, countdown); function countdown(event:TimerEvent) { var currentFrame:int = timer.currentCount % frames.length; for (var i:int = 0; i < frames.length; ++i) { frames[i].visible = (i == currentFrame); } } timer.start(); counter experiment My new class I'm working on loops through 10 different display objects that are numbers. For those following, I'm trying to make something like NumbersView.

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• STL vector performance

  - by iAdam

  STL vector class stores a copy of the object using copy constructor each time I call push_back. Wouldn't it slow down the program? I can have a custom linkedlist kind of class which deals with pointers to objects. Though it would not have some benefits of STL but still should be faster. See this code below: #include <vector> #include <iostream> #include <cstring> using namespace std; class myclass { public: char* text; myclass(const char* val) { text = new char[10]; strcpy(text, val); } myclass(const myclass& v) { cout << "copy\n"; //copy data } }; int main() { vector<myclass> list; myclass m1("first"); myclass m2("second"); cout << "adding first..."; list.push_back(m1); cout << "adding second..."; list.push_back(m2); cout << "returning..."; myclass& ret1 = list.at(0); cout << ret1.text << endl; return 0; } its output comes out as: adding first...copy adding second...copy copy The output shows the copy constructor is called both times when adding and when retrieving the value even then. Does it have any effect on performance esp when we have larger objects?

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• Are there any downsides in using C++ for network daemons?

  - by badcat

  Hey guys! I've been writing a number of network daemons in different languages over the past years, and now I'm about to start a new project which requires a new custom implementation of a properitary network protocol. The said protocol is pretty simple - some basic JSON formatted messages which are transmitted in some basic frame wrapping to have clients know that a message arrived completely and is ready to be parsed. The daemon will need to handle a number of connections (about 200 at the same time) and do some management of them and pass messages along, like in a chat room. In the past I've been using mostly C++ to write my daemons. Often with the Qt4 framework (the network parts, not the GUI parts!), because that's what I also used for the rest of the projects and it was simple to do and very portable. This usually worked just fine, and I didn't have much trouble. Being a Linux administrator for a good while now, I noticed that most of the network daemons in the wild are written in plain C (of course some are written in other languages, too, but I get the feeling that 80% of the daemons are written in plain C). Now I wonder why that is. Is this due to a pure historic UNIX background (like KISS) or for plain portability or reduction of bloat? What are the reasons to not use C++ or any "higher level" languages for things like daemons? Thanks in advance! Update 1: For me using C++ usually is more convenient because of the fact that I have objects which have getter and setter methods and such. Plain C's "context" objects can be a real pain at some point - especially when you are used to object oriented programming. Yes, I'm aware that C++ is a superset of C, and that C code is basically C++. But that's not the point. ;)

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• object / class methods serialized as well?

  - by Mat90

  I know that data members are saved to disk but I was wondering whether object's/class' methods are saved in binary format as well? Because I found some contradictionary info, for example: Ivor Horton: "Class objects contain function members as well as data members, and all the members, both data and functions, have access specifiers; therefore, to record objects in an external file, the information written to the file must contain complete specifications of all the class structures involved." and: Are methods also serialized along with the data members in .NET? Thus: are method's assembly instructions (opcodes and operands) stored to disk as well? Just like a precompiled LIB or DLL? During the DOS ages I used assembly so now and then. As far as I remember from Delphi and the following site (answer by dan04): Are methods also serialized along with the data members in .NET? sizeof(<OBJECT or CLASS>) will give the size of all data members together (no methods/procedures). Also a nice C example is given there with data and members declared in one class/struct but at runtime these methods are separate procedures acting on a struct of data. However, I think that later class/object implementations like Pascal's VMT may be different in memory.

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• python os.mkfifo() for Windows

  - by user302099

  Hello. Short version (if you can answer the short version it does the job for me, the rest is mainly for the benefit of other people with a similar task): In python in Windows, I want to create 2 file objects, attached to the same file (it doesn't have to be an actual file on the hard-drive), one for reading and one for writing, such that if the reading end tries to read it will never get EOF (it will just block until something is written). I think in linux os.mkfifo() would do the job, but in Windows it doesn't exist. What can be done? (I must use file-objects). Some extra details: I have a python module (not written by me) that plays a certain game through stdin and stdout (using raw_input() and print). I also have a Windows executable playing the same game, through stdin and stdout as well. I want to make them play one against the other, and log all their communication. Here's the code I can write (the get_fifo() function is not implemented, because that's what I don't know to do it Windows): class Pusher(Thread): def __init__(self, source, dest, p1, name): Thread.__init__(self) self.source = source self.dest = dest self.name = name self.p1 = p1 def run(self): while (self.p1.poll()==None) and\ (not self.source.closed) and (not self.source.closed): line = self.source.readline() logging.info('%s: %s' % (self.name, line[:-1])) self.dest.write(line) self.dest.flush() exe_to_pythonmodule_reader, exe_to_pythonmodule_writer =\ get_fifo() pythonmodule_to_exe_reader, pythonmodule_to_exe_writer =\ get_fifo() p1 = subprocess.Popen(exe, shell=False, stdin=subprocess.PIPE, stdout=subprocess.PIPE) old_stdin = sys.stdin old_stdout = sys.stdout sys.stdin = exe_to_pythonmodule_reader sys.stdout = pythonmodule_to_exe_writer push1 = Pusher(p1.stdout, exe_to_pythonmodule_writer, p1, '1') push2 = Pusher(pythonmodule_to_exe_reader, p1.stdin, p1, '2') push1.start() push2.start() ret = pythonmodule.play() sys.stdin = old_stdin sys.stdout = old_stdout

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• Is MarshalByRefObject special?

  - by Vilx-

  .NET has a thing called remoting where you can pass objects around between separate appdomains or even physical machines. I don't fully understand how the magic is done, hence this question. In remoting there are two base ways of passing objects around - either they can be serialized (converted to a bunch of bytes and the rebuilt at the other end) or they can inherit from MarshalByRefObject, in which case .NET makes some transparent proxies and all method calls are forwarded back to the original instance. This is pretty cool and works like magic. And I don't like magic in programming. Looking at the MarshalByRefObject with the Reflector I don't see anything that would set it apart from any other typical object. Not even a weird internal attribute or anything. So how is the whole transparent proxy thing organized? Can I make such a mechanism myself? Can I make an alternate MyMarshalByRefObject which would not inherit from MarshalByRefObject but would still act the same? Or is MarshalByRefObject receiving some special treatment by the .NET engine itself and the whole remoting feat is non-duplicatable by mere mortals?

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• How to catch non exist requested URL in Java servlet ?

  - by Frank

  My objects are stored online in two different places : <1 On my nmjava.com site, where I can put them in a directory called "Dir_My_App/Dir_ABC/" <2 On Google App Engine datastore When my Java app runs it checks both places for the objects, I designed the app so that it tries to get an object from a Url, it doesn't care whether it's an object in a directory or an object returned by a servlet. My_Object Get_Object(String Site_Url,String Object_Path) { ... get object by the name of Object_Path from the Site_Url ... } Now the request Url for my web site nmjava.com might look like this : http://nmjava.com/Dir_My_App/Dir_ABC/My_Obj_123 [ In a directory ] Or in the case of Google App Engine servlet : http://nm-java.appspot.com/Check_License/Dir_My_App/Dir_ABC/My_Obj_123 [ Non exist ] The "Object_Path" was generated by my app automatically. It can now get the object from my site by the above method like this : My_Object Get_Object("http://nmjava.com","/Dir_My_App/Dir_ABC/My_Obj_123"); In the Google App Engine, my servlet is running and ready to serve the object, if the request comes in correctly, but since I don't want to design my app to know whether the object is in one site's directory or in other site's datastore, I need to design the servlet to catch the non exist Url, such as the one above, and be able to make a call : My_Object Get_Object("http://nm-java.appspot.com/Check_License","/Dir_My_App/Dir_ABC/My_Obj_123"); So my question is : When a request comes into the servlet with a non exist Url, how should it catch it and analyze the url in order to respond properly, in my case it should know that : http://nm-java.appspot.com/Check_License/Dir_My_App/Dir_ABC/My_Obj_123 is asking for the object "My_Obj_123" [ ignore the dirs ] and return the object from the datastore. Now I'm getting this : Error: Not Found The requested URL /Check_License/Dir_My_App/Dir_ABC/My_Obj_123 was not found on this server. Where in my servlet and how do I detect the request for this non exist Url ?

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• Which class should store the lookup table?

  - by max

  The world contains agents at different locations, with only a single agent at any location. Each agent knows where he's at, but I also need to quickly check if there's an agent at a given location. Hence, I also maintain a map from locations to agents. I have a problem deciding where this map belongs to: class World, class Agent (as a class attribute) or elsewhere. In the following I put the lookup table, agent_locations, in class World. But now agents have to call world.update_agent_location every time they move. This is very annoying; what if I decide later to track other things about the agents, apart from their locations - would I need to add calls back to the world object all across the Agent code? class World: def __init__(self, n_agents): # ... self.agents = {} self.agent_locations = {} for id in range(n_agents): x, y = self.find_location() agent = Agent(self,x,y) self.agents.append(agent) self.agent_locations[x,y] = agent def update_agent_location(self, agent, x, y): del self.agent_locations[agent.x, agent.y] self.agent_locations[x, y] = agent def update(self): # next step in the simulation for agent in self.agents: agent.update() # next step for this agent # ... class Agent: def __init__(self, world, x, y): self.world = world self.x, self.y = x, y def move(self, x1, y1): self.world.update_agent_location(self, x1, y1) self.x, self.y = x1, y1 def update(): # find a good location that is not occupied and move there for x, y in self.valid_locations(): if not self.location_is_good(x, y): continue if self.world.agent_locations[x, y]: # location occupied continue self.move(x, y) I can instead put agent_locations in class Agent as a class attribute. But that only works when I have a single World object. If I later decide to instantiate multiple World objects, the lookup tables would need to be world-specific. I am sure there's a better solution... EDIT: I added a few lines to the code to show how agent_locations is used. Note that it's only used from inside Agent objects, but I don't know if that would remain the case forever.

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