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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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• Don't understand multiple parameter declarations in objective-c

  - by Blankman

  can someone clarify this for me: When there’s more than one argument, the arguments are declared within the method name after the colons. Arguments break the name apart in the declaration, just as in a message. For example: - (void)setWidth:(float)width height:(float)height; So in the above: method is for instance variables returns void parameter#1 is a float, named width. parameter#2 is a float,named height. But why is it hieght:(float)height; and not just: - (void)setWidth: (float)width (float)height;

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• ctypes import not working on python 2.5

  - by user551906

  Hi, I am trying to import ctypes, and I am using Python 2.5.5 installed using macports (on Mac OS X 10.6). I get an error saying "ImportError: No module named _ctypes" (see details below). As I understand it ctypes is supposed to come preinstalled for python 2.5. Any suggestions? thanks, Saurabh Error details: $ python Python 2.5.5 (r255:77872, Nov 30 2010, 00:05:47) [GCC 4.2.1 (Apple Inc. build 5659)] on darwin Type "help", "copyright", "credits" or "license" for more information. import ctypes Traceback (most recent call last): File "", line 1, in File "/opt/local/Library/Frameworks/Python.framework/Versions/2.5/lib/python2.5/ctypes/init.py", line 10, in from _ctypes import Union, Structure, Array ImportError: No module named _ctypes

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• Reference table values in a war against magic numbers

  - by Alex N.

  This question bugged me for years now and can't seem to find good solution still. I working in PHP and Java but it sounds like this maybe language-agnostic :) Say we have a standard status reference table that holds status ids for some kind of entity. Further let's assume the table will have just 5 values, and will remain like this for a long time, maybe edited occasionally with addition of a new status. When you fetch a row and need to see what status it is you have 2 options(as I see it at least) - put it straight ID values(magic numbers that is) or use a named constant. Latter seem much cleaner, the question though is where those named constants should leave? In a model class? In a class that uses this particular constant? Somewhere else?

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• Shell script variable problem

  - by user280288

  Hi all, I'm trying to write a shell script to automate a job for me. But i'm currently stuck. Here's the problem : I have a variable named var1 (a decreasing number from 25 to 0 and another variable named var${var1} and this equals to some string. then when i try to call var${var1} in anywhere in script via echo it fails. I have tried $[var$var1], ${var$var} and many others but everytime it fails and gives the value of var1 or says operand expected error. Thanks for your help

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• Runtime error in sml function

  - by Rpant

  I am writing this function in sml fun removeNodeswithNoIncoming((x:int,y)::xs,element:int) = if x=element then removeNodeswithNoIncoming (xs , element) else (x,y) :: removeNodeswithNoIncoming (xs , element) | removeNodeswithNoIncoming(nil,element) = nil; the function takes list of tuples [(0,0),(0,1)(1,2)] and another element 0 if first element of the tuples is same as second parameter , it removes it from the list The o/p for the above list should be [(1,2)] Unfortunately , the code is not working for the above input. Though there are other inputs for which it works - removeNodeswithNoIncomingEdge([(0,1),(0,2),(1,2)],0); stdIn:30.1-30.30 Error: unbound variable or constructor: removeNodeswithNoIncomi ngEdge - removeNodeswithNoIncomingEdge([(0,1),(0,2),(1,2),(1,4)],0); stdIn:1.2-1.31 Error: unbound variable or constructor: removeNodeswithNoIncoming Edge

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• Is there a way to cause a new C++ class instance to fail, if certain conditions in the contructor ar

  - by Jim Fell

  As I understand it, when a new class is instantiated in C++, a pointer to the new class is returned, or NULL, if there is insufficient memory. I am writing a class that initializes a linked list in the constructor. If there is an error while initializing the list, I would like the class instantiator to return NULL. For example: MyClass * pRags = new MyClass; If the linked list in the MyClass constructor fails to initialize properly, I would like pRags to equal NULL. I know that I can use flags and additional checks to do this, but I would like to avoid that, if possible. Does anyone know of a way to do this? Thanks.

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• C# - Why can't I enforce derived classes to have parameterless constructors?

  - by FrisbeeBen

  I am trying to do the following: public class foo<T> where T : bar, new { _t = new T(); private T _t; } public abstract class bar { public abstract void someMethod(); // Some implementation } public class baz : bar { public overide someMethod(){//Implementation} } And I am attempting to use it as follows: foo<baz> fooObject = new foo<baz>(); And I get an error explaining that 'T' must be a non-abstract type with a public parameterless constructor in order to use it as parameter 'T' in the generic type or method. I fully understand why this must be, and also understand that I could pass a pre-initialized object of type 'T' in as a constructor argument to avoid having to 'new' it, but is there any way around this? any way to enforce classes that derive from 'bar' to supply parameterless constructors?

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• How to find the entity with the greatest primary key?

  - by simpatico

  I've an entity LearningUnit that has an int primary key. Actually, it has nothing more. Entity Concept has the following relationship with it: @ManyToOne @Size(min=1,max=7) private LearningUnit learningUnit; In a constructor of Concept I need to retrieve the LearningUnit with the greatest primary key. If no LearningUnit exists yet I instantiate one. I then set this.learningUnit to the retrieved/instantied. Finally, I call the empty constructor of Concept in a try-catch block, to have the entitymanager do the cardinality check. If an exception is thrown (I expect one in the case that already another 7 Concepts are referring to the same LearningUnit. In that case, I case instantiate a new LearningUnit with a new greater primary key. Please, also point out, if any, clear pitfalls in my outlined algorithm above.

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• WPF StaticResource bound to subproperty

  - by mizipzor

  I have a class thats created as a resource: <Window.Resources> <Model:MyModel x:Key="model" /> </Window.Resources> The MyModel class has a cli property named Foo. I want the selected value in a combobox to be bound to this property. I thought I could do this but Im getting errors: <ComboBox SelectedItem="{Binding Source={StaticResource model.Foo}}" /> Heres the error: Cannot find resource named '{model.Foo}'. Where did I go wrong? What extra parameters do I need to specify to properly bind to a subproperty?

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• How should i be handling string Interning on deserialization?

  - by DayOne

  In the example below I am interning the string in the constructor which is fine. However when i deserialise the object from the binary formatter I don't think the string will be interned as the constructor should be called. How should I be ensuring the _name string is interned? ... or will it be interned ok? Thanks [Serializable] class City { private readonly string _name; public City(string t) { _name = string.Intern(t); } public string Name { get { return _name; } } public override string ToString() { return _name; } }

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• How can a class's memory-allocated address be determined from within the contructor?

  - by Jim Fell

  Is it possible to get the memory-allocated address of a newly instantiated class from within that class's constructor during execution of said constructor? I am developing a linked list wherein multiple classes have multiple pointers to like classes. Each time a new class instantiates, it needs to check its parent's list to make sure it is included. If I try to do something like this: MyClass() // contructor { extern MyClass * pParent; for ( int i = 0; i < max; i++ ) { pParent->rels[i] == &MyClass; // error } } I get this error: error C2275: 'namespace::MyClass' : illegal use of this type as an expression Any thoughts or suggestions would be appreciated. Thanks.

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• Problem with url_for in ActionMailer template

  - by macek

  I'm attempting to provide a confirmation link in my user welcome email and I'm getting the following Rails error: Need controller and action! It makes a fuss about this line: <p>Please take a moment to activate your account by going to: <%= link_to confirm_user_url(:id => @user.confirmation_code) %>.</p> In my development.rb environment, I have the following line: config.action_mailer.default_url_options = { :host => "localhost", :port => 3000 } There's no problem with the @user variable. I've tested the email with things like @user.username and @user.confirmation_code. I'm only getting trouble with url_for and named routes like confirm_user_url. When I check my routes with rake routes, confirm_user shows up, so it's not an issue with the named route not existing. I can't seem to figure it out. What gives?

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• Calling some functions before main in C

  - by minjang

  I'd like to do some stuffs before main function. I have multiple source files. In each file, there is some work that needs to be done before main. It was no problem in C++, but problematic with C. In C++, this can be done by two ways: Exploiting a constructor of a global class/struct. Calling a function to a global variable For example, static const int __register_dummy_ = __AddRegisterMetaInfo(...); However, in C, either ways is impossible. Obviously, there is no constructor. So, the first option is inherently impossible. I thought that the second option would be possible, but not compiled in C (I tested only with Visual C++. It gives C2099.). C only allows a constant to a non-automatic variable. Is there any way to call some functions before main?

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• Syncronizing indices of function pointer table to table contents

  - by Thomas Matthews

  In the embedded system I'm working on, we are using a table of function pointers to support proprietary Dynamic Libraries. We have a header file that uses named constants (#define) for the function pointer indices. These values are used in calculating the location in the table of the function's address. Example: *(export_table.c)* // Assume each function in the table has an associated declaration typedef void (*Function_Ptr)(void); Function_Ptr Export_Function_Table[] = { 0, Print, Read, Write, Process, }; Here is the header file: *export_table.h* #define ID_PRINT_FUNCTION 1 #define ID_READ_FUNCTION 2 #define ID_WRITE_FUNCTION 3 #define ID_PROCESS_FUNCTION 4 I'm looking for a scheme to define the named constants in terms of their location in the array so that when the order of the functions changes, the constants will also change. (Also, I would like the compiler or preprocessor to calculate the indices to avoid human mistakes like typeo's.)

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• How to make c# don't call destructor of a instance

  - by Bình Nguyên

  I have two forms and form1 needs to get data from form2, i use a parameter in form2 constructor to gets form1's instance like this: public form2(Form form1) { this.f = form1; } and in form1: Form form2 = new Form(this); But it seem form1 destruct was called when i closed form1. my question is how can i avoid this problem? EDIT: I have many typing mistakes in my question, i'm so sorry, fixed: I have two forms and form2 needs to get data from form1, i use a parameter in form1 constructor to gets form1's instance like this: private Form f; public form2(Form form1) { this.f = form1; } and in form1: Form form2 = new Form(this); But it seem form1 destruct was called when i closed form2. my question is how can i avoid this problem?

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• Selecting size of vector of vectors

  - by xbonez

  I have a class called Grid that declares a vector of vectors like this: typedef vector<int> row; typedef vector<row> myMatrix; myMatrix sudoku_; The constructor looks like this: grid::grid() : sudoku_(9,9) { } As you can see, the constructor is initializing it to be a 9x9 grid. How can I make it work so that the user is asked for a number, say n, and the grid is initialized n x n ?

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• Is it possible to start an activity from a regular java class?

  - by Yotam

  In my ActionBarSherlock I have the same menu items for all activities, so it seems unwise to define onClick handlers in each activity - they all do the same. Instead I created a class called MyClickListener that implements com.actionbarsherlock.view.MenuItem.OnMenuItemClickListener, and in there I have a simple switch block that starts the appropriate activity. Problem is that Intent constructor's first argument is of type Context, and even when I pass this to MyClickListener's constructor, I can't start any activity. The same goes for every method that has a Context object as a parameter. Is there a way to work around it? What is a context object? Thanks

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• Problems using Custom Layout in XML

  - by Kevin

  I've created a new GridLayout class that I want to use in an XML File. The class is in another project. I've created the attrs.xml file in the other project with my properties but when the constructor gets called with the AttributeSet, none of the values are set. In my xml for my screen layout, I refer to the layout with the following: xmlns:gridLayout="@com.mastertechsoftware.AndroidUtil:http://schemas.android.com/apk/res/com.mastertechsoftware.AndroidUtil" Not sure if that is right. I have the attrs.xml file being compiled to R.java in com/mastertechsoftware/AndroidUtil. All the right styleable values are there. In my constructor, I use: TypedArray a = c .obtainStyledAttributes(attrs, R.styleable.GridLayout); this.numRows = a.getInt(R.styleable.GridLayout_numRows, -1); Nothing comes back (-1 does but that means nothing is there) If I use int n = a.getIndexCount(); I get 0.

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• How to persist every new entity?

  - by simpatico

  I expect every instantiated entity to correspond to a tuple (& co) in the database. In the examples I see around, one always instantiates the entity (via a constructor) and then calls persist with that entity. I find this error-prone, and was wondering if it wasn't possible to have every instantiated entity automatically managed/persisted/reflected to the database (at least intended to). This also seems to prevent me from persisting instance variable entities. I.e. I've an entity which instantiates another (entities it has an association with) in its constructor.

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• What did I do wrong here when trying to unit test a class that references a web service

  - by zachary

  So I had a class that referenced a class that referenced another class that called a web service. So I learn how to create an interface using partial classes. I inject the web service through the constructor. Then my unit test fails because I am newing up the actual web service in the second level of the class. So I end up modifying all three classes to pass the web service down through the constructor... was not happy :-( gave up.... what should I be doing in this case?

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• How to avoid double construction of proxy with DynamicProxy::CreateClassProxyWithTarget?

  - by Belvasis

  I am decorating an existing object using the CreateClassProxyWithTarget method. However, the constructor and therefore, initialization code, is being called twice. I already have a "constructed" instance (the target). I understand why this happens, but is there a way to avoid it, other than using an empty constructor? Edit: Here is some code: First the proxy creation: public static T Create<T>(T i_pEntity) where T : class { object pResult = m_pGenerator.CreateClassProxyWithTarget(typeof(T), new[] { typeof(IEditableObject), typeof(INotifyPropertyChanged) , typeof(IMarkerInterface), typeof(IDataErrorInfo) }, i_pEntity, ProxyGenerationOptions.Default, new BindingEntityInterceptor<T>(i_pEntity)); return (T)pResult; } I use this for example with an object of the following class: public class KatalogBase : AuditableBaseEntity { public KatalogBase() { Values = new HashedSet<Values>(); Attributes = new HashedSet<Attributes>(); } ... } If i now call BindingFactory.Create(someKatalogBaseObject); the Values and Attributes properties are beeing initialized again.

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• Problems with starting windows service on windows xp SP3

  - by Michiel Peeters

  I'm currently facing a problem which I can not resolve and I really don't know what to do anymore. When I'm trying to start the service I receive the message: "The service is started but again also stopped, this because that some of the services will stop if they have nothing to do, for example the performance logs and the alerts service". I've looked into the Windows Logs but nothing is written there which could describe why my service is all the time stopping. I've also tried to fire the windows service via the command prompt which gives me the message: "The service is not started, but the service didn't return any faults.". I've tried to remove all keys which references to my service, which didn't resolve the issue. I've searched on google (maybe not good enough) to find an answer but I didn't found any. I did found some websites which describes what I could do, but all of these suggestions didn't work. This is kinda ** because I do not know where to look. I do not have any error message, i do not have any id which i can use to search on. I really don't know where to start and I hope you guys can help me on this one. Detailed explanation about the windows service OS: Windows XP SP3 .Net Framework: .Net 4.0 Client Profile Language: C# Development environment: Visual Studio 2010 Professional (but Visual Studio 2012 RC is installed) Communications: WCF (Named Pipes), WCF (BasicHTTPBinding) Named Pipes: I have chosen for this solution because I wanted to communicate from a windows service to a windows form application. It worked now for quite some time but suddenly my windows service shuts it self down and I couldn't restart it anymore. There are two named pipes services implemented: An event service which will send any notification to the windows form application and an management service which gives my windows form application the possibility to maintain my windows service. BasicHTTPBinding: The basic http binding makes the connection to a central server. This connection is then used for streaming information from the client to the server. I do not know which additional information you will need, but if you guys need something then I'll try to give it as detailed as possible. Thank you in advance.

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• Confusion over C++ new operator and classes

  - by Nils

  Hi all I created a simple class in C++ which has a private dynamic array. In the constructor I initialize the array using new and in the destructor I free it using delete. When I instantiate the class using Class a = Class(..); it works as expected, however it seems I cannot instantiate it using the new operator (Like Class *a = new Class(..);), I always get a segmentation fault. What I don't understand is when I should use new to instantiate a class and when just call the constructor or should it be possible to instantiate a class either with new or by just calling the constructor. float** A = new float*[3]; for (int i=0; i<3; i++) { A[i] = new float[3]; } A[0][0] = 3; A[0][1] = 3; A[0][2] = 4; A[1][0] = 5; A[1][1] = 6; A[1][2] = 7; A[2][0] = 1; A[2][1] = 2; A[2][2] = 3; Matrix *M = new Matrix(A, 3, 3); delete[] A; delete M; Below the class definition.. class Matrix { private: int width; int height; int stride; float* elements; public: Matrix(float** a, int n, int m); ~Matrix(); }; Matrix::Matrix(float** a, int n, int m) { // n: num rows // m: elem per rows elements = new float[n*m]; for (int i=0; i<n; i++) { for (int j=0; j<m; j++) { elements[i*n + j] = a[n][m]; } } } Matrix::~Matrix() { delete[] elements; }

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• read contents of a sql table into a data grid view

  - by syedsaleemss

  Im using c# .net windows application form. i have created a database named "resources" in SQL server 2005. In that i have a table named "resourcetable" which has two columns. now i need to read the data in the table into a datagridview. I can do this by using the connection string and querry by giving the table name. But my problem is i have a button and if i click on that button, an open dialog box should open and i should be able to select a database amomng many databases and in that selected database i have to select one table amomg many tables. i.e select a table ofa particular database. and the contents of that table are to be displayed in a datagridview.

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