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  • Using locks inside a loop

    - by Xaqron
    // Member Variable private readonly object _syncLock = new object(); // Now inside a static method foreach (var lazyObject in plugins) { if ((string)lazyObject.Metadata["key"] = "something") { lock (_syncLock) { if (!lazyObject.IsValueCreated) lazyObject.value.DoSomething(); } return lazyObject.value; } } Here I need synchronized access per loop. There are many threads iterating this loop and based on the key they are looking for, a lazy instance is created and returned. lazyObject should not be created more that one time. Although Lazy class is for doing so and despite of the used lock, under high threading I have more than one instance created (I track this with a Interlocked.Increment on a volatile shared int and log it somewhere). The problem is I don't have access to definition of Lazy and MEF defines how the Lazy class create objects. My questions: 1) Why the lock doesn't work ? 2) Should I use an array of locks instead of one lock for performance improvement ?

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  • Using a class with const data members in a vector

    - by Max
    Given a class like this: class Foo { const int a; }; Is it possible to put that class in a vector? When I try, my compiler tells me it can't use the default assignment operator. I try to write my own, but googling around tells me that it's impossible to write an assignment operator for a class with const data members. One post I found said that "if you made [the data member] const that means you don't want assignment to happen in the first place." This makes sense. I've written a class with const data members, and I never intended on using assignment on it, but apparently I need assignment to put it in a vector. Is there a way around this that still preserves const-correctness?

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  • Suggestions for performance improvement surrounding sending email notifications?

    - by jcmoney
    It takes around a couple of seconds for my app to execute the code to send an email right now on a test server with nothing much else running. Not sure if this is typical/expected. I'm also using the php framework Kohana's email helper and not php's mail directly out of convenience if that matters. Is it always just better to schedule a cron job to send emails every 5 min or so? Or should I be able to send emails immediately and I'm just not doing something right? What the script does is insert a row into the db and notifies the relevant group that the row was created. The groups are usually < 20 people so I just do a loop calling Kohana's email helper each time for each member of the group.

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  • mysql stored procedures using php

    - by neo skosana
    I have a stored procedure: delimiter // create procedure userlogin(in eml varchar(50)) begin select * from users where email = eml; end// delimiter ; And the php: $db = new mysqli("localhost","root","","houseDB"); $eml = "[email protected]"; $sql = $db-query("CALL userlogin('$eml')"); $result = $sql-fetch_array(); The error that I get from the browser when I run the php script: Fatal error: Call to a member function fetch_array() on a non-object... I am using phpmyadmin version 3.2.4 and mysql client version 5.1.41. Please help. Thank you.

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  • Parsing String into multiple variable length String (C#)

    - by Nassign
    I am currently trying to convert a VB6 program into C#. There was extensive use of string splitting into structure. For example, Dim Sample AS String Sample = "John Doe New York Test Comment" Public Type Struct1 Name As String * 15 Address As String * 10 Comment As String * 20 End Type Dim dataStruct As Struct1 Set dataStruct = Sample When the dataStruct is set, it will automatically split value into the 3 structure member. Is there a special function to do this in C#. The only way I know how to do this is thru Attributes/Annotation describing the length and start position of string. Any other suggestion?

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  • Is it possible to use an incremental value within a variable name whilst declaring it within a loop?

    - by Jack
    Hi, I'm creating function which will read different XML files each time that will contain different amounts of the same nodes. I have already created a loop which stores the ID of each node into an array, and now I want to create variables for each array member which store attributes of the node with each ID. Because the number of nodes will be different for every XML document my function reads, I cannot manually assign variables for the attributes of each node ID not knowing how many to assign, so I have created a loop which runs specific to the number of items I have stored in the array. Inside this loop I was hoping to have something like: for (i=0; i<array.length; i++) { var ID + i + width = exampleheight var ID + i + height = exampleheight } I know this doesn't work, but was trying to outline what I am looking to find out. Is it possible to use some kind of variable or random number when declaring a variable?

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  • ListView created programmatically - emptyView doesn't show

    - by Yorick
    I've created custom ListView programmatically, and set view to show when ListAdapter is empty but nothing shows on the screen in that case, what can be wrong? public PlayerList(Context context, Activity activity) { super(context); mParent = activity; setOnItemClickListener( new OnItemClickListener() { public void onItemClick(AdapterView<?> parent, View view, int position, long id) { ... } }; List<PlayerInfo> players; players = getPlayerList(); // here size of players == 0 setAdapter(new PlayersAdapter(this.getContext(), R.id.player_name, players)); LayoutInflater vi = (LayoutInflater)mParent.getSystemService(Context.LAYOUT_INFLATER_SERVICE); emptyView = vi.inflate(R.layout.empty_view, null); // emptyView is View, and member of PlayerList this.setEmptyView(emptyView); }

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  • Lifetime of implicitly casted temporaries

    - by Answeror
    I have seen this question. It seems that regardless of the cast, the temporary object(s) will "survive" until the fullexpression evaluated. But in the following scenario: void foo(boost::tuple<const double&> n) { printf("%lf\n", n.get<0>()); } int main() { foo(boost::tuple<const double&>(2));//#1 foo(boost::make_tuple(2));//#2 return 0; } 1 run well, but 2 do not. And MSVC gave me a warning about 2: "reference member is initialized to a temporary that doesn't persist after the constructor exits" Now I am wondering why they both make a temporary "double" object and pass it to boost::tuple<const double&> and only 2 failed.

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  • Does C++ require a destructor call for each placement new?

    - by Josh Haberman
    I understand that placement new calls are usually matched with explicit calls to the destructor. My question is: if I have no need for a destructor (no code to put there, and no member variables that have destructors) can I safely skip the explicit destructor call? Here is my use case: I want to write C++ bindings for a C API. In the C API many objects are accessible only by pointer. Instead of creating a wrapper object that contains a single pointer (which is wasteful and semantically confusing). I want to use placement new to construct an object at the address of the C object. The C++ object will do nothing in its constructor or destructor, and its methods will do nothing but delegate to the C methods. The C++ object will contain no virtual methods. I have two parts to this question. Is there any reason why this idea will not work in practice on any production compiler? Does this technically violate the C++ language spec?

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  • When I use WinForms (C#) designer in VS2010, it still generates code that StyleCop complains about.

    - by Hamish Grubijan
    Some problems that I recall (there may be more): Includes regions Does not use this. prefix for member variables and methods Includes comments like the one below ( having // by itself catches the eye of StyleCop) // // fileNameTextBox // If I make a change to the text, and then open the designer again, and screws up my previously perfected fruits of hard labor. How did / would you solve this problem? I heard but did not personally experience a similar problem with WPF. How did / would you fix that? Thanks.

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  • Prolog: find all numbers of unique digits that can be formed from a list of digits

    - by animo
    The best thing I could come up with so far is this function: numberFromList([X], X) :- digit(X), !. numberFromList(List, N) :- member(X, List), delete(List, X, LX), numberFromList(LX, NX), N is NX * 10 + X. where digit/1 is a function verifying if an atom is a decimal digit. The numberFromList(List, N) finds all the numbers that can be formed with all digits from List. E.g. [2, 3] -> 23, 32. but I want to get this result: [2, 3] -> 2, 3, 23, 32 I spent a lot of hours thinking about this and I suspect you might use something like append(L, _, List) at some point to get lists of lesser length. I would appreciate any contribution.

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  • Help with Magento and related products

    - by Anthony
    I have a customer product page that literally lives beside the catalog/product/view.phtml page. It's basically identical to that page with a few small exceptions. It's basically a 'product of the day' type page so I can't combine it with the regular product page since I have to fetch the data from the DB and perform a load to get the product information $_product = Mage::getModel('catalog/product')->load($row['productid']); To make a long story short, everything works (including all children html blocks) with the singular exception of the related products. After the load I save the product into the registry with Mage::register('product', $_product); and then attempt to load the related products with: echo $this->getLayout()->createBlock('catalog/product_view')->setTemplate('catalog/product/list/related.phtml')->toHtml();` All of which give back the error: Fatal error: Call to a member function getSize() on a non-object in catalog/product/list/related.phtml on line 29`, and line 29 is <?php if($this->getItems()->getSize()): ?>`. Any help getting the relateds to load would be appreicated.

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  • Pointer to struct, containing pointer to an object, for which I want to call a function

    - by user1795609
    So I've created an ADT which is a singly linked list made up of nodes. These Nodes each have a pointer to an object in them called data. Class Structure { struct Node { Object *data; Node *next; }; }; Node *head; I am trying to call a function in the object, like this: head = new Node; head -> data = new Object(); head -> next = NULL; cout << head -> data.print(); I keep getting the following error at compile. error: request for member 'print' in 'head-Structure::Node::data', which is of non-class type 'Object'*

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  • How to call a function though Control.BeginInvoke in a signal-slot-like fashion?

    - by Dimitri C.
    I'd like a delegate that calls a function in a different thread when it is invoked. Currently, I'm using the following implementation: delegate void someFunctionDelegate(); //... someFunctionDelegate callBackFunction = someForm.SomeFunction; someForm.Invoke(someFunctionDelegate); However, I'd like a more compact form, combining both the someForm instance and the SomeForm.SomeFunction member function. I'm thinking of something like this: var callBackFunction = new AsynchronousCrossThreadDelegate(someForm, SomeForm.SomeFunction); callBackFunction(); // Should call someForm.BeginInvoke(SomeForm.SomeFunction); Is there a way to do so in C#/.NET? Update I'm looking for a solution that will work for functions with 0 or more parameters.

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  • Find a variable with a given value in VS2008

    - by Aaron
    I have an instance variable with several members, many of which have their own members and so on. Using the debugger and watch variables, I found a string variable with a specific value that I need by diving into this variable's members. However, after spending some time on other things and coming back to this, I am now unable to find where this value is located. When I have my application paused, is there a way to search the values of variables in the current context for a given value? To clarify, if I have the given structure: myVariable | |--aMember1 | |--subMember = "A value" | |--aMember2 |--subMember = "Another value" Is there a way (possibly using the watch list in VS debugger) to search myVariable for any member or submember with the value "A value", returning to me the path myVariable->aMember->subMember?

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  • Binding to object properties in C++

    - by Rich.Carpenter
    I've seen in WPF where you can bind control values to properties of other controls. How is that binding accomplished in C++? For example, if I have a class called Car and a guage control called RPM, how do I tie the value of RPM to the member variable Car.RPM, so that when Car.RPM changes, it is automatically (as in without a specific update call coded by me) reflected by the RPM control? General answers or directions to pertinent resources would be fine also, as I'm just beginning to dabble in C++ and haven't had much Google luck with this particular question.

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  • Barcode field length

    - by bestattendance
    I'm writing some attendance software. Each member will have an ID card with a barcode which they will use to sign in to events. How long should the barcode field be in my database? I'd like to accept Code 39 and Code 128 barcodes. I know these are variable length codes, so what should I set the max length to? Thanks! EDIT: My clients will be using a variety of third-party barcode printing tools.

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  • std::make_shared as a default argument does not compile

    - by Mark Bryant
    In Visual C++ (2008 and 2010), the following code does not compile with the following error: #include <memory> void Foo( std::shared_ptr< int > test = ::std::make_shared< int >( 5 ) ) { } class P { void Foo( std::shared_ptr< int > test = ::std::make_shared< int >( 5 ) ) { } }; error C2039: 'make_shared' : is not a member of '`global namespace'' error C3861: 'make_shared': identifier not found It is complaining about the definition of P::Foo() not ::Foo(). Does anybody know why it is valid for Foo() to have a default argument with std::make_shared but not P::Foo()?

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  • g++ doesn't think I'm passing a reference

    - by Ben Jones
    When I call a method that takes a reference, g++ complains that I'm not passing a reference. I thought that the caller didn't have to do anything different for PBR. Here's the offending code: //method definition void addVertexInfo(VertexInfo &vi){vertexInstances.push_back(vi);} //method call: sharedVertices[index]->addVertexInfo(VertexInfo(n1index, n2index)); And here's the error: GLUtils/GLMesh.cpp: In member function 'void GLMesh::addPoly(GLIndexedPoly&)': GLUtils/GLMesh.cpp:110: error: no matching function for call to 'SharedVertexInfo::addVertexInfo(VertexInfo)' GLUtils/GLMesh.h:93: note: candidates are: void SharedVertexInfo::addVertexInfo(VertexInfo&)

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  • Manage bad_alloc exception in C++ construtor

    - by Jimmy zhang
    I have Java experience and recently am doing some C++ coding. My question is that if I have class A, in which I have to instantiate class B and class C as two of the member variables of A. If in the constructor of A, should I assume that allocations of class B and C never fail, and handle the bad allocation exception in the destructor of A? If I don't make that assumption, meaning that I add some try catch block to catch bad_alloc of class B and class C, then if the allocation exception occurs, should I do clean up in the constructor of A? What are the recommended practices? If "new" generates a bad allocation, what value does the pointer carry?

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  • Is there a name for a pure-data Objective-C class?

    - by BrianEnigma
    This is less of a code-specific question and more of an Objective-C nomenclature question. In C you have struct for pure data. In Enterprise Java, you have "bean" classes that are purely member variables with getters and setters, but no business logic. In Adobe FLEX, you have "Value Objects". In Objective-C, is there a proper name for an object (descended from NSObject, of course) that simply has ivars and getters/setters (or @property/@synthesize, if you want to get fancy) and no real business logic? A more concrete example might be a simple class with getters and setters for filename, file size, description, and assorted other metadata. You could then take a bunch of these and easily throw them into a container (NSDictionary, NSArray) without the need for messy NSValue wrapping of a C struct. It is also a little more structure than putting, say, a bunch of loosely-typed child NSDictionaries into a parent container object.

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  • How can I receive the "scroll box" type scroll events from a DataGridView?

    - by Simon
    I have a DataGridView, and I'm listening to its Scroll event. This gives me a ScrollEventArgs object whose Type member is supposed to tell me the type of scroll event that has occurred. On the MSDN documentation page it says I should be able to detect movement of the scroll box by listening for events with types ThumbPosition, ThumbTrack, First, Last and EndScroll. However, when I drag the scroll box, I only get events of type LargeDecrement and LargeIncrement. How do I get access to the ThumbPosition, ThumbTrack, First, Last and EndScroll events?

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  • Another thread safe queue implementation

    - by jensph
    I have a class, Queue, that I tried to make thread safe. It has these three member variables: std::queue<T> m_queue; pthread_mutex_t m_mutex; pthread_cond_t m_condition; and a push and pop implemented as: template<class T> void Queue<T>::push(T value) { pthread_mutex_lock( &m_mutex ); m_queue.push(value); if( !m_queue.empty() ) { pthread_cond_signal( &m_condition ); } pthread_mutex_unlock( &m_mutex ); } template<class T> bool Queue<T>::pop(T& value, bool block) { bool rtn = false; pthread_mutex_lock( &m_mutex ); if( block ) { while( m_queue.empty() ) { pthread_cond_wait( &m_condition, &m_mutex ); } } if( !m_queue.empty() ) { value = m_queue.front(); m_queue.pop(); rtn = true; } pthread_mutex_unlock( &m_mutex ); return rtn; } Unfortunately there are occasional issues that may be the fault of this code. That is, there are two threads and sometimes thread 1 never comes out of push() and at other times thread 2 never comes out of pop() (the block parameter is true) though the queue isn't empty. I understand there are other implementations available, but I'd like to try to fix this code, if needed. Anyone see any issues? The constructor has the appropriate initializations: Queue() { pthread_mutex_init( &mMutex, NULL ); pthread_cond_init( &mCondition, NULL ); } and the destructor, the corresponding 'destroy' calls.

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  • IDisposable, does it really matter

    - by adrianm
    Coming from C/C++ a long time ago I still have a habit of ensuring that all resources are cleaned up correctly. I always ensure Dispose is called on IDisposable classes and implement Dispose patterns in my classes containing disposable objects. However, in my environment I'm more or less the only one doing this. Others just don't understand what I'm doing and think my code is more difficult to understand. They just create database connections, open streams etc without calling Close or Dispose. Sometimes they set a local or member variable to "Nothing" at the end of a method (guess their background). My problem is that their code works just as well as mine. Code that over time creates thousands of database connection objects just works. So, ignoring any arguments about code correctness, following guidelines etc, does IDiposable really matter? Has anyone actually ran out of resources from not Disposing objects?

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  • how can I have a teammate restart heroku server from his machine

    - by josh
    I have a rails app up on heroku. Sometimes the server bombs out and I have to go to the console and execute heroku restart so that servers get restarted. This seems to fix the problem. However, I am not on my machine all the time. I would like to have a team member have this capability as well. For this to happen...what does he need to do? Does he need to first have access to the github repository so that he can push and pull code to the repository and then install heroku on his machine? Can this be done without git hub? can he just install heroku?

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