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  • Getting meaningful error messages from fstream's in C++

    - by Hassan Syed
    What is the best way to get meaningful file access error messages, in a portable way from std::fstreams ? The primitiveness of badbits and failbits is getting to be bit annoying. I have written my own exception hierarchies against win32 and POSIX before, and that was far more flexible than the way the STL does it. I am getting "basic::ios_clear" as an error message from the what method of a downcasted catch (std::exception) of a fstream which has exceptions enabled. This doesn't mean much to me, although I do know what the problem is I'd like my program to be a tad more informative so that when I start deployment a few months later my life will be easier. Is there anything in Boost to extract meaningful messages out of the ofstream's implementation cross platform and cross STL implementation ?

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  • Change in asp.net page life cycle event

    - by xyz
    Has there been any change in page life cycle event in asp.net 3.5(I mean some addition or any modification in the exisitng one)? Sorry to ask in this way as because recently in an interview I have been asked by an interviewer. I dare to ask him the answer for this even after the interview! If the asnwer is yes, kindly give some detailing about that; even a tutorial link will also do if no explicit explanation. Thanks

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  • Can you explicitly set a structure layout/alignment in C++ as you can in C#?

    - by Gary Willoughby
    In C# you have nice alignment attributes such as this: [StructLayout(LayoutKind.Explicit)] public struct Message { [FieldOffset(0)] public int a; [FieldOffset(4)] public short b; [FieldOffset(6)] public int c; [FieldOffset(22)] //Leave some empty space just for the heck of it. public DateTime dt; } Which gives you fine control on how you need your structure to be layed out in memory. Is there such a thing in standard C++?

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  • About the String#substring() method

    - by alain.janinm
    If we take a look at the String#substring method implementation : new String(offset + beginIndex, endIndex - beginIndex, value); We see that a new String is created with the same original content (parameter char [] value). So the workaround is to use new String(toto.substring(...)) to drop the reference to the original char[] value and make it eligible for GC (if no more references exist). I would like to know if there is a special reason that explain this implementation. Why the method doesn't create herself the new shorter String and why she keeps the full original value instead? The other related question is : should we always use new String(...) when dealing with substring?

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  • Comet with multiple channels

    - by mark_dj
    Hello, I am writing an web app which needs to subscribe to multiple channels via javascript. I am using Atmosphere and Jersey as backend. However the jQuery plugin they work with only supports 1 channel. I've start buidling my own implementation. Now it works oke, but when i try to subscribe to 2 channels only 1 channel gets notified. Is the XMLHttpRequest blocking the rest of the XMLHttpRequests? Here's my code: function AtmosphereComet(url) { this.Connected = new signals.Signal(); this.Disconnected = new signals.Signal(); this.NewMessage = new signals.Signal(); var xhr = null; var self = this; var gotWelcomeMessage = false; var readPosition; var url = url; var onIncomingXhr = function() { if (xhr.readyState == 3) { if (xhr.status==200) // Received a message { var message = xhr.responseText; console.log(message); if(!gotWelcomeMessage && message.indexOf("") -1) { gotWelcomeMessage = true; self.Connected.dispatch(sprintf("Connected to %s", url)); } else { self.NewMessage.dispatch(message.substr(readPosition)); } readPosition = this.responseText.length; } } else if (this.readyState == 4) { self.disconnect(); } } var getXhr = function() { if ( window.location.protocol !== "file:" ) { try { return new window.XMLHttpRequest(); } catch(xhrError) {} } try { return new window.ActiveXObject("Microsoft.XMLHTTP"); } catch(activeError) {} } this.connect = function() { xhr = getXhr(); xhr.onreadystatechange = onIncomingXhr; xhr.open("GET", url, true); xhr.send(null); } this.disconnect = function() { xhr.onreadystatechange = null; xhr.abort(); } this.send = function(message) { } } And the test code: var connection1 = AtmosphereConnection("http://192.168.1.145:9999/botenveiling/b/product/status/2", AtmosphereComet); var connection2 = AtmosphereConnection("http://192.168.1.145:9999/botenveiling/b/product/status/1", AtmosphereComet); var output = function(msg) { alert(output); }; connection1.NewMessage.add(output); connection2.NewMessage.add(output); connection1.connect(); In AtmosphereConnection I instantiate the given AtmosphereComet with "new". I iterate over the object to check if it has to methods: "send", "connect", "disconnect". The reason for this is that i can switch the implementation later on when i complete the websocket implementation :) However I think the problem rests with the XmlHttpRequest object, or am i mistaken? P.S.: signals.Signal is a js observer/notifier library: http://millermedeiros.github.com/js-signals/ Testing: Firefox 3.6.1.3

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  • c++ "interface"-like classes similar to Java?

    - by William the Coderer
    In Java, you can define an interface as a class with no actual code implementation, but only to define the methods that a class must implement. Those types can be passed as parameters to methods and returned from methods. In C++, a pure virtual class can't be used as a parameter or return type, from what I can tell. Any way to mimic Java's interface classes? I have a string class in C++, and several subclasses for different encodings (like UTFxxx, ISOxxx, etc) that derive from the base string class. However, since there are so many different encodings, the base class has no meaningful implementation. But it would serve well as an interface if I could handle it as its own object and calls to that object would call on the correct subclass it was inherited to.

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  • Get computed font size for DOM element in JS

    - by Pekka
    Is it possible to detect the computed font-size of a DOM element, taking into consideration generic settings made elsewhere (In the body tag for example), inherited values, and so on? A framework-independent approach would be nice, as I'm working on a script that should work standalone, but that is not a requirement of course. Background: I'm trying to tweak CKEditor's font selector plugin (source here) so that it always shows the font size of the current cursor position (as opposed to only when within a span that has an explicit font-size set, which is the current behaviour).

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  • Web Service returning object with null fields

    - by Xaiter
    Never seen this one before. WebService.Implementation imp = new WebService.Implementation(); WebService.ImplementationRequest req = new WebService.ImplementationRequest(); return imp.GetValue(req); The object that imp returns is not null. It's returning an ImplementationResponse, as expected. But all of the fields in that object are null. Which is not expected. The WebService, currently, just returns some constant dummy data. We've tested this on another developer's machine, works just fine. I suppose I should also note that the WebService should throw an exception if I pass null into the GetValue method. It doesn't. Not for me. Any idea what could be wrong with my environment that could make a WebService return an object, but make every value in that object null? And somehow 'magically' return this mystery object when it should be throwing an exception?

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  • How to define RequestMapping prioritization

    - by James Skidmore
    I have a situation where I need the following RequestMapping: @RequestMapping(value={"/{section}"}) ...method implementation here... @RequestMapping(value={"/support"}) ...method implementation here... There is an obvious conflict. My hope was that Spring would resolve this automatically and map /support to the second method, and everything else to the first, but it instead maps /support to the first method. How can I tell Spring to allow an explicit RequestMapping to override a RequestMapping with a PathVariable in the same place? (Edit - this is simplified, I know that having those two RequestMapping alone wouldn't make much sense)

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  • Qt: any way to automatically generate QSharedData-based structures?

    - by Eye of Hell
    Hello. Qt has a build-in supprt for creating objects with integrated reference counting via QSharedData and QSharedDataPointer. All wordks great, but for each such object i need to write a lot of code: QSharedData-based implementation class with constructor and copy constructor, object class itsef with accessor methods for each filed. For a simple structures with 5-10 fields this requires really lot of near same code. Is it some ways to automate such classes generation? Maybe it's some generators exists that take a short description and automatically generates implementation class and object class with all accessors?

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  • Separation of domain and ui layer in a composite

    - by hansmaad
    Hi all, i'm wondering if there is a pattern how to separate the domain logic of a class from the ui responsibilities of the objects in the domain layer. Example: // Domain classes interface MachinePart { CalculateX(in, out) // Where do we put these: // Draw(Screen) ?? // ShowProperties(View) ?? // ... } class Assembly : MachinePart { CalculateX(in, out) subParts } class Pipe : MachinePart { CalculateX(in, out) length, diamater... } There is an application that calculates the value X for machines assembled from many machine parts. The assembly is loaded from a file representation and is designed as a composite. Each concrete part class stores some data to implement the CalculateX(in,out) method to simulate behaviour of the whole assembly. The application runs well but without GUI. To increase the usability a GUi should be developed on top of the existing implementation (changes to the existing code are allowed). The GUI should show a schematic graphical representation of the assembly and provide part specific dialogs to edit several parameters. To achieve these goals the application needs new functionality for each machine part to draw a schematic representation on the screen, show a property dialog and other things not related to the domain of machine simulation. I can think of some different solutions to implement a Draw(Screen) functionality for each part but i am not happy with each of them. First i could add a Draw(Screen) method to the MachinePart interface but this would mix-up domain code with ui code and i had to add a lot of functionality to each machine part class what makes my domain model hard to read and hard to understand. Another "simple" solution is to make all parts visitable and implement ui code in visitors but Visitor does not belong to my favorite patterns. I could derive UI variants from each machine part class to add the UI implementation there but i had to check if each part class is suited for inheritance and had to be careful on changes to the base classes. My currently favorite design is to create a parallel composite hierarchy where each component stores data to define a machine part, has implementation for UI methods and a factory method which creates instances of the corresponding domain classes, so that i can "convert" a UI assembly to a domain assembly. But there are problems to go back from the created domain hierarchy to the UI hierarchy for showing calculation results in the drawing for example (imagine some parts store some values during the calculation i want to show in the schematic representation after the simluation). Maybe there are some proven patterns for such problems?

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  • c++11 atomic ordering: extended total order memory_order_seq_cst for locks

    - by itaj
    There's this note in c++11 29.3-p3: [ Note: Although it is not explicitly required that S include locks, it can always be extended to an order that does include lock and unlock operations, since the ordering between those is already included in the "happens before" ordering. - end note ] What does it mean by "always"? I can understand that any certain implementation can be designed to support such an extended S. But in some general implementation that wasn't designed for it, I don't see that S can be extended so. I had sent this question to comp.std.c++ but got no answers there. http://groups.google.com/group/comp.std.c++/browse_frm/thread/5242fa70d0594d1b#

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  • What is the benefits and drawbacks of using header files?

    - by vodkhang
    I had some experience on programming languages like Java, C#, Scala as well as some lower level programming language like C, C++, Objective - C. My observation is that low level languages separate out header files and implementation files while other higher level programming language never separate it out. They use some identifiers like public, private, protected to do the jobs of header files. I saw one benefit of using header file (in some book like Code Complete), they talk about that using header files, people can never look at our implementation file and it helps with encapsulation. A drawback is that it creates too many files for me. Sometimes, it looks like verbose. It is just my thought and I don't know if there are any other benefits and drawbacks that people ever see and work with header file This question may not relate directly to programming but I think that if I can understand better about programming to interface, design software.

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  • Class destructor memory handling in C++

    - by wyatt
    What potential memory leaks won't an implicit destructor handle? I know that if you have anything stored on the heap it won't handle it, and if you have a connection to a file or a database, that needs to be handled manually. Is there anything else? What about, say, non-base data types like vectors? Also, in an explicit destructor, need you destroy non-heap variables which would have been destroyed by the implicit, or are they handled automatically? Thanks

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  • Stored Procedure IDENTITY_INSERT

    - by Jacob
    I'm recently change my data table, I remove column and add a new column that define as identity = True and identity seed = 1, identity increment = 1. When i tried to insert data to this table by STORE PROCEDURE i get this exception: An explicit value for the identity column in table 'AirConditioner' can only be specified when a column list is used and IDENTITY_INSERT is ON. I saw that i need to add this lines: SET IDENTITY_INSERT [dbo].[AirConditioner] ON and finally OFF I added and its still throw an exception... My store procedure is attached as a picture

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  • Which libraries use the "We Know Where You Live" optimization for std::make_shared?

    - by KnowItAllWannabe
    Over two years ago, Stephan T. Lavavej described a space-saving optimization he implemented in Microsoft's implementation of std::make_shared, and I know from speaking with him that Microsoft has nothing against other library implementations adopting this optimization. If you know for sure whether other libraries (e.g., for Gnu C++, Clang, Intel C++, plus Boost (for boost::make_shared)) have adopted this implementation, please contribute an answer. I don't have ready access to that many make_shared implementations, nor am I wild about digging into the bowels of the ones I have to see if they've implemented the WKWYL optimization, but I'm hoping that SO readers know the answers for some libraries off-hand. I know from looking at the code that as of Boost 1.52, the WKWYL optimization had not been implemented, but Boost is now up to version 1.55. Note that this optimization is different from std::make_shared's ability to avoid a dedicated heap allocation for the reference count used by std::shared_ptr. For a discussion of the difference between WKWYL and that optimication, consult this question.

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  • Counting bits set in a .Net BitArray Class

    - by Sam
    I am implementing a library where I am extensively using the .Net BitArray class and need an equivalent to the Java BitSet.Cardinality() method, i.e. a method which returns the number of bits set. I was thinking of implementing it as an extension method for the BitArray class. The trivial implementation is to iterate and count the bits set (like below), but I wanted a faster implementation as I would be performing thousands of set operations and counting the answer. Is there a faster way than the example below? count = 0; for (int i = 0; i < mybitarray.Length; i++) { if (mybitarray [i]) count++; }

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  • iphone memory management: alloc and retain properties.

    - by Jonathan
    According to the docs, you do one release per alloc or retain (etc) However what about when using retain propertys? eg: HEADER @property(retain)UIView *someView; IMPLEMENTATION /*in some method*/ UIView *tempView = [[UIView alloc] init]; //<<<<<ALLOC - retain count = +1 [tempView setBackgroundColor:[UIColor redColor]]; self.someView = tempView; ///<<<<<RETAIN - retain count = +2 [tempView release]; ///should I do this? or a different version of the IMPLEMENTATION self.someView = [[UIView alloc] init]; //<<<<<ALLOC & RETAIN - retain count = +2 //now what??? [self.someView release]; ???? EDIT: I didn't make it clear, but I meant what to do in both circumstances, not just the first.

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  • How to approach copying objects with smart pointers as class attributes?

    - by tomislav-maric
    From the boost library documentation I read this: Conceptually, smart pointers are seen as owning the object pointed to, and thus responsible for deletion of the object when it is no longer needed. I have a very simple problem: I want to use RAII for pointer attributes of a class that is Copyable and Assignable. The copy and assignment operations should be deep: every object should have its own copy of the actual data. Also, RTTI needs to be available for the attributes (their type may also be determined at runtime). Should I be searching for an implementation of a Copyable smart pointer (the data are small, so I don't need Copy on Write pointers), or do I delegate the copy operation to the copy constructors of my objects as shown in this answer? Which smart pointer do I choose for simple RAII of a class that is copyable and assignable? (I'm thinking that the unique_ptr with delegated copy/assignment operations to the class copy constructor and assignment operator would make a proper choice, but I am not sure) Here's a pseudocode for the problem using raw pointers, it's just a problem description, not a running C++ code: // Operation interface class ModelOperation { public: virtual void operate = (); }; // Implementation of an operation called Special class SpecialModelOperation : public ModelOperation { private: // Private attributes are present here in a real implementation. public: // Implement operation void operate () {}; }; // All operations conform to ModelOperation interface // These are possible operation names: // class MoreSpecialOperation; // class DifferentOperation; // Concrete model with different operations class MyModel { private: ModelOperation* firstOperation_; ModelOperation* secondOperation_; public: MyModel() : firstOperation_(0), secondOperation_(0) { // Forgetting about run-time type definition from input files here. firstOperation_ = new MoreSpecialOperation(); secondOperation_ = new DifferentOperation(); } void operate() { firstOperation_->operate(); secondOperation_->operate(); } ~MyModel() { delete firstOperation_; firstOperation_ = 0; delete secondOperation_; secondOperation_ = 0; } }; int main() { MyModel modelOne; // Some internal scope { // I want modelTwo to have its own set of copied, not referenced // operations, and at the same time I need RAII to work for it, // as soon as it goes out of scope. MyModel modelTwo (modelOne); } return 0; }

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  • Getting Type mismatch for my function

    - by Sandy Williams
    I am getting an error message i.e. Type mismatch: 'EMXWEB_IE_LAUNCH' Line (1): "' ==============================================================================". the function is Option Explicit Public Function EMXWEB_IE_LAUNCH (dicArguments, sErrMsg) Dim strVersion Dim strExeVersion Dim WshShell Dim strEMXWebBrowserTitleBarText Dim ie Const strFunctionName = "EMXWEB_IE_LAUNCH" Set ie = CreateObject( "InternetExplorer.Application" ) ie.Navigate "www.google.com" ie.Visible=True End Function Could any one let me know where i am wrong and why i am getting this issue

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