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  • To "null" or not to "null" my class's attributes

    - by Helper Method
    When I write a class in Java, I like to initialize the attributes which are set to a default value directly and attributes which are set by the caller in the constructor, something like this: public class Stack<E> { private List<E> list; private size = 0; public Stack(int initialCapacity) { list = new ArrayList<E>(initialCapacity); } // remainder omitted } Now suppose I have a Tree class: public class Tree<E> { private Node<E> root = null; // no constructor needed, remainder omitted } Shall I set the root attribute to null, to mark that it is set to null by default, or omit the null value?

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  • .NET Performance: Deep Recursion vs Queue

    - by JeffN825
    I'm writing a component that needs to walk large object graphs, sometimes 20-30 levels deep. What is the most performant way of walking the graph? A. Enqueueing "steps" so as to avoid deep recursion or B. A DFS (depth first search) which may step many levels deep and have a "deep" stack trace at times. I guess the question I'm asking is: Is there a performance hit in .NET for doing a DFS that causes a "deep" stack trace? If so, what is the hit? And would I better better off with some BFS by means of queueing up steps that would have been handled recursively in a DFS? Sorry if I'm being unclear. Thanks.

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  • win7 + vc7.1 + mfc = stackoverflow

    - by fogbit
    Hello! I've moved my vc7.1 project from WInXP to Win7. After rebuilding i got stackoverflow error in function _malloc_dbg when i start the program. "Unhandled exception at 0x0051bf0f in XXX.exe: 0xC00000FD: Stack overflow." Call stack: msvcr71d.dll!_malloc_dbg(unsigned int nSize=140, int nBlockUse=2, const char * szFileName=0x10267784, int nLine=163) msvcr71d.dll!_calloc_dbg(unsigned int nNum=1, unsigned int nSize=140, int nBlockUse=2, const char * szFileName=0x10267784, int nLine=163) msvcr71d.dll!_mtinit() msvcr71d.dll!_CRTDLL_INIT(void * hDllHandle=0x10200000, unsigned long dwReason=1, void * lpreserved=0x0018fd24) I tried to set up different stacksizes in project options (from 10 to 100 mbytes), in all cases i got this error. How can i fix this?

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  • Rails streaming file download

    - by Leonard Teo
    I'm trying to implement a file download with Rails. I want to eventually migrate this code to using S3 to serve the file. I've copied the Rails send_file code almost verbatim and I cannot seem to get it to stream a file to the user. What happens is that it sends 'a' file to the user, but the downloaded file itself simply contains the text.inspect of the Proc: # What am I doing wrong here? options = {} options[:length] = File.size(file.path) options[:filename] = File.basename(file.path) send_file_headers! options render :status => 200, :text => Proc.new { |response, output| len = 4096 File.open(file.path, 'rb') do |fh| while buf = fh.read(len) output.write(buf) end end } Ps: I've read in a number of other posts that it's not advisable to send files through the Rails stack, and if possible serve using the web server, or in the case of S3 use the hashed URL it can provide. Yes, we really do want to serve the file through the Rails stack.

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  • Polymorphic classes in templates

    - by soxarered
    Let's say we have a class hierarchy where we have a generic Animal class, which has several classes directly inherit from it (such as Dog, Cat, Horse, etc..). When using templates on this inheritance hierarchy, is it legal to just use SomeTemplateClass<Animal> and then shove in Dogs and Cats and Horses into this templated object? For example, assume we have a templated Stack class, where we want to host all sorts of animals. Can I simply state Stack<Animal> s; Dog d; s.push(d); Cat c; s.push(c);

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  • How do I set properties related to the calling method's scope?

    - by Thiado de Arruda
    I'm not looking for a way to associate values with a thread using the 'SetData' method. I need to store some kind of data that will only exist during the scope of a calling method, could be the immediate parent or any other call that is made down on the stack. For example: void SomeMethod() { string someInfo = "someInfo"; SomeOtherMethod(); object data = GetDataOnCurrentScope("someKey"); } void SomeOtherMethod() { SetDataOnParentScope("someKey", somevalue); } In this case both the 'someInfo' local variable and the data set with the "someKey" key will disapear after 'SomeMethod' returns. Is something like this possible? This may go against the rules of a stack, but who knows if someone has an idea...

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  • Open source framework à la Microsoft Sync Framework suggestions?

    - by drskol
    We are implementing a warehouse management system atop an open source stack (Java, web services & friends). In this system, we want to integrate many mobile devices which should also be capable of adequate online/offline functionality, e.g. preparing database inserts while a mobile device is temporarily unconnected, and performing them on the backend database when reconnected. For a .NET stack, Microsoft Sync Framework would be a perfect solution, e.g. to do database replication and hoarding. Can anyone suggest an open source alternative to the MS Sync Framework and possibly describe his experiences with it? Thanks in advance for any answers.

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  • error: expected `;' before '{' token - What is the cause?

    - by melee
    Here is my implementation file: using namespace std; #include <iostream> #include <iomanip> #include <string> #include <stack> //line 5 #include "proj05.canvas.h" //----------------Constructor----------------// Canvas::Canvas() //line 10 { Title = ""; Nrow = 0; Ncol = 0; image[][100]; // line 15 position.r = 0; position.c = 0; } //-------------------Paint------------------// line 20 void Canvas::Paint(int R, int C, char Color) { cout << "Paint to be implemented" << endl; } The errors I'm getting are these: proj05.canvas.cpp: In function 'std::istream& operator>>(std::istream&, Canvas&)': proj05.canvas.cpp:11: error: expected `;' before '{' token proj05.canvas.cpp:22: error: a function-definition is not allowed here before '{' token proj05.canvas.cpp:24: error: expected `}' at end of input proj05.canvas.cpp:24: error: expected `}' at end of input These seem like simple syntax errors, but I am not sure what's wrong. Could someone decode these for me? I'd really appreciate it, thanks for your time! EDIT Here is the definition of Canvas in my .h file: #ifndef CANVAS_H #define CANVAS_H #include <iostream> #include <iomanip> #include <string> #include <stack> class Canvas { public: Canvas(); void Paint(int R, int C, char Color); const int Nrow; const int Ncol; string Title; int image[][100]; stack<int> path; struct PixelCoordinates { unsigned int r; unsigned int c; } position; }; #endif

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  • Emulate back button in multi-view TabActivity

    - by ZelluX
    Hi, all I have a TabActivity with several tabs. Each tab corresponds to a specific view, and those views may further switch to other views. For example, one of my tabs displays RSS feed list, after user clicks one of the RSS feed, it will switch to a view displaying a list of articles, and after user clicks one of the titles, a full article view will be displayed. I'm going to add support for "back" button in my application. For instance, in a full article view, after user presses the "back" button, it should switch back to the article list view. And if user presses it the "back" button again, my application should switch back to the feed list view. My idea is to maintain a Stack<View> during navigation, and every time user presses the "back" button, the program will pop a View out of the stack, and set it as the current view. But I would like to know how to set current view in TabHost. Many thanks.

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  • How to remove the shadow from a librarystack

    - by red-X
    I'm currently in a project where I need a LibraryStack with no visuals at all, so it would just show the content. If I just remove the background a shadow stays in view which I cant seem to remove... This code looks like: <s:LibraryStack Background="Transparent"> <s:LibraryStackItem Background="AliceBlue"/> <s:LibraryStackItem Background="Bisque"/> <s:LibraryStackItem Background="Salmon"/> </s:LibraryStack> This stack is just for explaining purposes, the actual stack is added in the code behind in c#. So preferably any answers that would be usefull to add in c#.

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  • Postfix and right-associative operators in LR(0) parsers

    - by Ian
    Is it possible to construct an LR(0) parser that could parse a language with both prefix and postfix operators? For example, if I had a grammar with the + (addition) and ! (factorial) operators with the usual precedence then 1+3! should be 1 + 3! = 1 + 6 = 7, but surely if the parser were LR(0) then when it had 1+3 on the stack it would reduce rather than shift? Also, do right associative operators pose a problem? For example, 2^3^4 should be 2^(3^4) but again, when the parser have 2^3 on the stack how would it know to reduce or shift? If this isn't possible is there still a way to use an LR(0) parser, possibly by converting the input into Polish or Reverse Polish notation or adding brackets in the appropriate places? Would this be done before, during or after the lexing stage?

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  • Implementation communication protocols in C/C++

    - by MeThinks
    I am in the process of starting to implement some proprietary communication protocol stack in software but not sure where to start. It is the kind of work I have not done before and I am looking for help in terms of resources for best/recommended approaches. I will be using c/c++ and I am free to use use libraries (BSD/BOOST/Apache) but no GPL. I have used C++ extensively so using the features of C++ is not a problem. The protocol stack has three layers and it is already fully specified and formally verified. So all I need to do is implemented and test it fully in the specified languages. Should also mention that protocol is very simple but can run on different devices over a reliable physical transport layer Any help with references/recommendations will be appreciated. I am willing to use a different language if only to help me understand how to implement them but I will have to eventually resort to the language of choice.

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  • Application crashes when popViewControllerAnimated is called while scrolling

    - by Aldrich
    In one screen I have a custom toolbar with a "close" button in it, and a UIScrollView. In the screen that preceded this one I had pushed the current screen into the navigation stack. I had also disabled the navigation toolbar for a larger display area and so the close button would instead be used to call: - (void)doClose { [self.navigationController popViewControllerAnimated:YES]; } Now here's the problem: the application crashes when the close button is pressed, while the UIScrollView is moving. Here's the debugger stack trace: 0 __forwarding__ 1 __forwarding_prep_0___ 2 -[UIToolbarButton setHighlighted:] 3 -[UIControl(Static) _unhighlight] 4 __NSFireDelayedPerform ... and I do have the following line in the debugger console: *** -[CALayer setOpacity:]: message sent to deallocated instance 0x718d250 (sometimes setOpacity would be setNeedsDisplay or something related) There won't be any crashes while the scrollview is at rest. What is happening?

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  • new operator overwriting an existing object

    - by dvpdiner2
    I have a custom FastStack class, implemented as a fixed size array and an index into that array. In my copy constructor, I allocate the array and then assign each object from the copy's array into the new array. There's some refcounting in the objects on the stack, hence assignment is used rather than a simple copy. The problem is that when allocating the array, it sometimes overwrites part of the other stack's array. As can be expected, this leads to eventual segmentation faults when that data is dereferenced. class FastStack { private: int m_size, m_ptr; ObjectRef* m_stack; public: FastStack(int size) : m_size(size), m_ptr(-1) { m_stack = new ObjectRef[m_size]; } FastStack(const FastStack& copy) : m_size(copy.m_size), m_ptr(copy.m_ptr) { long a = (long)copy.m_stack[0]; m_stack = new ObjectRef[m_size]; if ((long)copy.m_stack[0] != a) fprintf(stderr, "\nWe have a serious problem!\n\n"); for (int i = 0; i <= m_ptr; i++) m_stack[i] = copy.m_stack[i]; } ~FastStack() { delete[] m_stack; } }; class ObjectRef { private: DataObj* m_obj; public: ObjectRef() : m_obj(0) { } ObjectRef(DataObj* obj) : m_obj(obj) { if (m_obj) m_obj->addRef(); } ObjectRef(const ObjectRef& obj) : m_obj(obj.m_obj) { if (m_obj) m_obj->addRef(); } ~ObjectRef() { if (m_obj) m_obj->delRef(); } ObjectRef& operator=(DataObj* obj) { if (obj) obj->addRef(); if (m_obj) m_obj->delRef(); m_obj = obj; return *this; } ObjectRef& operator=(const ObjectRef& obj) { if (obj.m_obj) obj.m_obj->addRef(); if (m_obj) m_obj->delRef(); m_obj = obj.m_obj; return *this; } }; I see that "We have a serious problem!" line shortly before a segfault, and stepping through it with gdb I can see that one of the ObjectRefs created by new has the same address as the other stack's array. My first instinct is to say that new should never be allocating memory that is already in use, but that clearly seems to be the case here and I am at a complete loss as to what can be done. Added: At the time that I see this happen, m_size = 2 and m_ptr = 0.

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  • Spring 3, Java EE 6

    - by arg20
    I'm learning Java EE 6. I've seen how much progress it has achieved in this release of the umbrella specification. EJBs 3.1 are far easier and more lightweight than previous versions, and CDI is amazing. I'm not familiar with Spring, but I often read that it offered some neat features that the Java EE stack didn't. Yet I also read now that JEE has caught up, and can now fully compete with Spring. I know that choosing from both depends on many factors, but if we only focus on features, say the latest trends etc. Which one has the leading edge?. Can Spring 3 offer some assets The JAVA EE 6 stack can't? Also, what about Seam framework? From what I read it's like java ee 6 but with some additions?

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  • show activity indicator while loading ViewController

    - by Crystal
    I have a ViewController that takes time to load its views. When I run Instruments, I see from the home screen, if I tap on the icon that pushes that view controller onto the stack, it's half laying out the views, and half getting the data for the views. I tried adding an activity indicator to display on the home screen over the button when the button is pressed to push the LongRunningViewController onto the stack. So I basically do this: - (IBAction)puzzleView:(id)sender { dispatch_async(dispatch_get_main_queue(), ^{ [self.activityIndicator startAnimating]; }); PuzzleViewController *detailViewController = [[[PuzzleViewController alloc] init] autorelease]; [self.navigationController pushViewController:detailViewController animated:YES]; [self.activityIndicator stopAnimating]; }

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  • C++: Question about freeing memory

    - by Martijn Courteaux
    On Learn C++, they wrote this to free memory: int *pnValue = new int; // dynamically allocate an integer *pnValue = 7; // assign 7 to this integer delete pnValue; pnValue = 0; My question is: "Is the last statement needed to free the memory correctly, completly?" I thought that the pointer *pnValue was still on the stack and new doesn't make any sense to the pointer. And if it is on the stack it will be cleaned up when the application leaves the scope (where the pointer is declared in), isn't it?

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  • How Android retrieves info of the Stacked Activities which are killed when memory goes low.

    - by taranfx
    I was reading on how Activities communicate and how the calls stack up on top of each other. But at any instant when the OS(or dalvik) is low on resources, it can choose to kill Paused or Stopped Activities. In this scenario, how do we restore previous state of the activity(in which it was before getting killed) when we reach the same activity on our way back. Does stack store the state as well as references to the Activity? Aren't their chances of achieving a different state when we re-constuct activity (onCreate)?

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  • [GWT] StackLayoutPanel and MVP

    - by Stine
    Hello! Think there might be something about this MVP approach I have completely misunderstood. Currently I am struggling to apply the MVP pattern to the part of my application consisting of a StackLayoutPanel (accordion). To me it seems natural to have a presenter and a view per stack... but how do I allow the different presenters to react when the user switch the state of the stack panel? If someone could sketch an application of the MVP pattern in the case of an accordion application I would be really, really grateful! This is really getting on my nerves! ;D Thanks a lot from Stine :)

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  • Deleted nib still displayed when controller is pushed

    - by yahuie
    I have an application with a UINavcontroller under a tab bar controller. To create the navigation model I want, I push a container UIView object onto the stack to manage additional views(Thanks Frank). When I created the container class, an associated nib file was created along with it. I at first used that nib file, but it turned out it was better not to. So I deleted the nib (and selected 'also move to trash'). The problem is that it still shows up when I push its view controller onto the stack. I have tried emptying the cache in xcode and restarting xcode. What am I missing?

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  • Can I get parameter names/values procedurally from the currently executing function?

    - by Pwninstein
    I would like to do something like this: public MyFunction(int integerParameter, string stringParameter){ //Do this: LogParameters(); //Instead of this: //Log.Debug("integerParameter: " + integerParameter + // ", stringParameter: " + stringParameter); } public LogParameters(){ //Look up 1 level in the call stack (if possible), //Programmatically loop through the function's parameters/values //and log them to a file (with the function name as well). //If I can pass a MethodInfo instead of analyzing the call stack, great. } I'm not even sure what I want to do is possible, but it would be very nice to be able to automatically output parameter names/values at runtime to a file without explicitly writing the code to log them. Thanks!

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