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  • Reading a file with a supplied name in C++

    - by Cosmina
    I must read a file with a given name (it's caled "hamlet.txt"). The class used to read the file is defined like this #ifndef READWORDS_H #define READWORDS_H /** * ReadWords class. Provides mechanisms to read a text file, and return * capitalized words from that file. */ using namespace std; #include <string> #include <fstream> class ReadWords { public: /** * Constructor. Opens the file with the default name "text.txt". * Program exits with an error message if the file does not exist. */ ReadWords(); /** * Constructor. Opens the file with the given filename. * Program exits with an error message if the file does not exist. * @param filename - a C string naming the file to read. */ ReadWords(char *filename); My definition of the members of the classis this: #include<string> #include<fstream> #include<iostream> #include "ReadWords.h" using namespace std; ReadWords::ReadWords() { wordfile.open("text.txt"); if( !wordfile ) { cout<<"Errors while opening the file!"<<endl; } } ReadWords::ReadWords(char *filename) { wordfile.open(filename); if ( !wordfile ) { cout<<"Errors while opening the file!"<<endl; } wordfile>>nextword; } And the main to test it. using namespace std; #include #include #include "ReadWords.h" int main() { char name[30]; cout<<"Please input a name for the file that you wish to open"; cin>>name; ReadWords x( name[] ); } When I complie it gives me the error: main.cpp:14: error: expected primary-expression before ']' token I know it's got something to do with the function ReadWords( char *filename), but I do not know what. Any help please?

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  • avoiding the tedium of optional parameters

    - by Kyle
    If I have a constructor with say 2 required parameters and 4 optional parameters, how can I avoid writing 16 constructors or even the 10 or so constructors I'd have to write if I used default parameters (which I don't like because it's poor self-documentation)? Are there any idioms or methods using templates I can use to make it less tedious? (And easier to maintain?)

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  • initializing a vector of custom class in c++

    - by Flamewires
    Hey basically Im trying to store a "solution" and create a vector of these. The problem I'm having is with initialization. Heres my class for reference class Solution { private: // boost::thread m_Thread; int itt_found; int dim; pfn_fitness f; double value; std::vector<double> x; public: Solution(size_t size, int funcNo) : itt_found(0), x(size, 0.0), value(0.0), dim(30), f(Eval_Functions[funcNo]) { for (int i = 1; i < (int) size; i++) { x[i] = ((double)rand()/((double)RAND_MAX))*maxs[funcNo]; } } Solution() : itt_found(0), x(31, 0.0), value(0.0), dim(30), f(Eval_Functions[1]) { for (int i = 1; i < 31; i++) { x[i] = ((double)rand()/((double)RAND_MAX))*maxs[1]; } } Solution operator= (Solution S) { x = S.GetX(); itt_found = S.GetIttFound(); dim = S.GetDim(); f = S.GetFunc(); value = S.GetValue(); return *this; } void start() { value = f (dim, x); } /* plus additional getter/setter methods*/ } Solution S(30, 1) or Solution(2, 5) work and initalizes everything, but I need X of these solution objects. std::vector<Solution> Parents(X) will create X solutions with the default constructor and i want to construct using the (int, int) constructor. Is there any easy(one liner?) way to do this? Or would i have to do something like: size_t numparents = 10; vector<Solution> Parents; Parents.reserve(numparents); for (int i = 0; i<(int)numparents; i++) { Solution S(31, 0); Parents.push_back(S); }

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  • Implementing default constructors

    - by James
    Implement the default constructor, the constructors with one and two int parameters. The one-parameter constructor should initialize the first member of the pair, the second member of the pair is to be 0. Overload binary operator + to add the pairs as follows: (a, b) + (c, d) = (a + c, b + d); Overload the - analogously. Overload the * on pairs ant int as follows: (a, b) * c = (a * c, b * c). Write a program to test all the member functions and overloaded operators in your class definition. You will also need to write accessor (get) functions for each member. The definition of the class Pairs: class Pairs { public: Pairs(); Pairs(int first, int second); Pairs(int first); // other members and friends friend istream& operator>> (istream&, Pair&); friend ostream& operator<< (ostream&, const Pair&); private: int f; int s; }; Self-Test Exercise #17: istream& operator (istream& ins, Pair& second) { char ch; ins ch; // discard init '(' ins second.f; ins ch; // discard comma ',' ins second.s; ins ch; // discard final '(' return ins; } ostream& operator<< (ostream& outs, const Pair& second) { outs << '('; outs << second.f; outs << ", " ;// I followed the Author's suggestion here. outs << second.s; outs << ")"; return outs; }

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  • C++ using this pointer in constructors

    - by gilbertc
    In c++, during a class constructor, I started a new thread with 'this' pointer as a parameter which will be used in the thread extensively (say, calling member functions). Is that a bad thing to do? Why and what are the consequences? Thanks, Gil.

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  • Creating instance in java class

    - by aladine
    Please advise me the difference between two ways of declaration of java constructor public class A{ private static A instance = new A(); public static A getInstance() { return instance; } public static void main(String[] args) { A a= A.getInstance(); } } AND public class B{ public B(){}; public static void main(String[] args) { B b= new B(); } } Thanks

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  • call_user_function_array() and __construct

    - by John
    I'm working on a simple framework, and I'm having a slight problem. I'd like to use call_user_function_array() to pass parameters to a function. That's fine, except the function I want to pass it to is __construct. I can't create an instance of an object with cufa(), and by instantiating an object, and then using cufa to call that instance's __construct(), I run into problems with a broken class because I'm calling the constructor twice (and one time it's called wrong.)

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  • Inlining an array of non-default constructible objects in a C++ class

    - by porgarmingduod
    C++ doesn't allow a class containing an array of items that are not default constructible: class Gordian { public: int member; Gordian(int must_have_variable) : member(must_have_variable) {} }; class Knot { Gordian* pointer_array[8]; // Sure, this works. Gordian inlined_array[8]; // Won't compile. Can't be initialized. }; As even beginner C++ users know, the language guarantees that all members are initialized when constructing a class. And it doesn't trust the user to initialize everything in the constructor - one has to provide valid arguments to the constructors of all members before the body of the constructor even starts. Generally, that's a great idea as far as I'm concerned, but I've come across a situation where it would be a lot easier if I could actually have an array of non-default constructible objects. The obvious solution: Have an array of pointers to the objects. This is not optimal in my case, as I am using shared memory. It would force me to do extra allocation from an already contended resource (that is, the shared memory). The entire reason I want to have the array inlined in the object is to reduce the number of allocations. This is a situation where I would be willing to use a hack, even an ugly one, provided it works. One possible hack I am thinking about would be: class Knot { public: struct dummy { char padding[sizeof(Gordian)]; }; dummy inlined_array[8]; Gordian* get(int index) { return reinterpret_cast<Gordian*>(&inlined_array[index]); } Knot() { for (int x = 0; x != 8; x++) { new (get(x)) Gordian(x*x); } } }; Sure, it compiles, but I'm not exactly an experienced C++ programmer. That is, I couldn't possibly trust my hacks less. So, the questions: 1) Does the hack I came up with seem workable? What are the issues? (I'm mainly concerned with C++0x on newer versions of GCC). 2) Is there a better way to inline an array of non-default constructible objects in a class?

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  • CodeContracts: How to fullfill Require in Ctor using this() call?

    - by mafutrct
    I'm playing around with Microsoft's CodeContracts and encountered a problem I was unable to solve. I've got a class with two constructors: public Foo (public float f) { Contracts.Require(f > 0); } public Foo (int i) : this ((float)i) {} The example is simplified. I don't know how to check the second constructor's f for being 0. Is this even possible with Contracts?

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  • C# Strange Behavior

    - by Betamoo
    I have a custom struct : struct A { public int y; } a custom class with empty constuctor: class B { public A a; public B() { } } and here is the main: static void Main(string[] args) { B b = new B(); b.a.y = 5;//No runtime errors! Console.WriteLine(b.a.y); } When I run the above program, it does not give me any errors, although I did not initialize struct A in class B constructor..'a=new A();'

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  • How to define an aspectj pointcut that picks out all constructors of a class that has a specific annotation?

    - by PineForest
    Here is the annotation: @Target(value = ElementType.TYPE) @Retention(value = RetentionPolicy.RUNTIME) @Inherited public @interface MyAnnotation { String name(); } Here is one annotated class: @MyAnnotation(name="foo") public class ClassA { public ClassA() { // Do something } } Here is a second annotated class: @MyAnnotation(name="bar") public class ClassB { public ClassB(String aString) { // Do something } } I am looking for an aspectj pointcut that correctly matches the constructors for ClassA and ClassB while not matching any other constructor for any other class NOT annotated by MyAnnotation.

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  • purpose of php consutructor

    - by Bharanikumar
    Hi , Am working in the classes and object class structure , but not extream level , Just class and function , then in one place instantiation . that's it , not much big functions like __construct etc , Please tell me very simply , 1.what is th purpose of constructor ad destructor , But i know theoretical explanation school level , But i am expecting something like in real time , which situation we have to use, and is there any example for that please tell me, Regards

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  • What's the proper term for a function inverse to a constructor - to unwrap a value from a data type?

    - by Petr Pudlák
    Edit: I'm rephrasing the question a bit. Apparently I caused some confusion because I didn't realize that the term destructor is used in OOP for something quite different - it's a function invoked when an object is being destroyed. In functional programming we (try to) avoid mutable state so there is no such equivalent to it. (I added the proper tag to the question.) Instead, I've seen that the record field for unwrapping a value (especially for single-valued data types such as newtypes) is sometimes called destructor or perhaps deconstructor. For example, let's have (in Haskell): newtype Wrap = Wrap { unwrap :: Int } Here Wrap is the constructor and unwrap is what? The questions are: How do we call unwrap in functional programming? Deconstructor? Destructor? Or by some other term? And to clarify, is this/other terminology applicable to other functional languages, or is it used just in the Haskell? Perhaps also, is there any terminology for this in general, in non-functional languages? I've seen both terms, for example: ... Most often, one supplies smart constructors and destructors for these to ease working with them. ... at Haskell wiki, or ... The general theme here is to fuse constructor - deconstructor pairs like ... at Haskell wikibook (here it's probably meant in a bit more general sense), or newtype DList a = DL { unDL :: [a] -> [a] } The unDL function is our deconstructor, which removes the DL constructor. ... in The Real World Haskell.

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  • Dependency Injection Constructor Madness

    - by JP
    I find that my constructors are starting to look like this: public MyClass(Container con, SomeClass1 obj1, SomeClass2, obj2.... ) with ever increasing parameter list. Since "Container" is my dependency injection container, why can't I just do this: public MyClass(Container con) for every class? What are the downsides? If I do this, it feels like I'm using a glorified static. Please share your thoughts on IoC and Dependency Injection madness. Thanks in advance. -JP

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  • Using reflection to retrieve constructor used to instantiate attribute

    - by summatix
    How can I retrieve information about how an attribute was instantiated? Consider I have the following class definitions: [AttributeUsage(AttributeTargets.Class)] public class ExampleAttribute : Attribute { public ExampleAttribute(string value) { Value = value; } public string Value { get; private set; } } [ExampleAttribute("test")] public class Test { } The new .NET 4.0 MemberInfo.GetCustomAttributesData method: foreach (var attribute in typeof(Test).GetCustomAttributesData()) { Console.WriteLine(attribute); } outputs [Example.ExampleAttribute("test")]. Is there another way to retrieve this same information, preferably using the MemberInfo.GetCustomAttributes method?

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  • XmlSerializer giving FileNotFoundException at constructor

    - by Irwin
    An application I've been working with is failing when i try to serialize types. A statement like this: XmlSerialzer lizer = new XmlSerializer(typeof(MyType)); Produces: System.IO.FileNotFoundException occurred Message="Could not load file or assembly '[Containing Assembly of MyType].XmlSerializers, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null' or one of its dependencies. The system cannot find the file specified." Source="mscorlib" FileName="[Containing Assembly of MyType].XmlSerializers, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" FusionLog="" StackTrace: at System.Reflection.Assembly._nLoad(AssemblyName fileName, String codeBase, Evidence assemblySecurity, Assembly locationHint, StackCrawlMark& stackMark, Boolean throwOnFileNotFound, Boolean forIntrospection) at System.Reflection.Assembly.nLoad(AssemblyName fileName, String codeBase, Evidence assemblySecurity, Assembly locationHint, StackCrawlMark& stackMark, Boolean throwOnFileNotFound, Boolean forIntrospection) I don't define any special serializers for my class.

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  • WPF MVVM ViewModel constructor designmode

    - by Snake
    Right, I've got a main wpf window: <Window x:Class="NorthwindInterface.MainWindow" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:ViewModels="clr-namespace:NorthwindInterface.ViewModels" Title="MainWindow" Height="350" Width="525"> <Window.DataContext> <ViewModels:MainViewModel /> </Window.DataContext> <ListView ItemsSource="{Binding Path=Customers}"> </ListView> </Window> And the MainViewModel is this: class MainViewModel : INotifyPropertyChanged { public event PropertyChangedEventHandler PropertyChanged = delegate { }; public MainViewModel() { Console.WriteLine("test"); using (NorthwindEntities northwindEntities = new NorthwindEntities()) { this.Customers = (from c in northwindEntities.Customers select c).ToList(); } } public List<Customer> Customers { get;private set; } Now the problem is that in designermode I can't see my MainViewModel, it highlights it saying that it can't create an instance of the MainViewModel. It is connecting to a database. That is why (when I comment the code the problem is solved). But I don't want that. Any solutions on best practices around this?

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  • Ambiguous function/constructor call in C#

    - by Ahmed Said
    The following code causes a compiler error, as it is ambiguous call but the problem if we use object instead of ArrayList no error happens and the string version works fine; Do you have an explanation for that? class A { public A(string x) { Console.WriteLine("string"); } public A(ArrayList x) { Console.WriteLine("ArrayList"); } } static void Main(string[] args) { A o = new A(null); }

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  • F# Class with Generics : 'constructor deprecated' error

    - by akaphenom
    I am trying to create a a class that will store a time series of data - organized by groups, but I had some compile errors so I stripped down to the basics (just a simple instantiation) and still can't overcome the compile error. I was hoping some one may have seen this issue before. Clas is defined as: type TimeSeriesQueue<'V, 'K when 'K: comparison> = class val private m_daysInCache: int val private m_cache: Map<'K, 'V list ref > ref; val private m_getKey: ('V -> 'K) ; private new(getKey) = { m_cache = ref Map.empty m_daysInCache = 7 ; m_getKey = getKey ; } end So that looks OK to me (it may not be, but doesnt have any errors or warnings) - the instantiation gets the error: type tempRec = { someKey: string ; someVal1: int ; someVal2: int ; } let keyFunc r:tempRec = r.someKey // error occurs on the following line let q = new TimeSeriesQueue<tempRec, string> keyFunc This construct is deprecated: The use of the type syntax 'int C' and 'C ' is not permitted here. Consider adjusting this type to be written in the form 'C' NOTE This may be simple stupidity - I am just getting back from holiday and my brain is still on time zone lag...

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  • Scala Array constructor?

    - by Lukasz Lew
    scala> val a = Array [Double] (10) a: Array[Double] = Array(10.0) scala> val a = new Array [Double] (10) a: Array[Double] = Array(0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0) Why these two expressions have different semantics?

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  • Simple factory to retrieve files using constructor dependency injection

    - by mrblah
    I want to create a class, that is flexible so I can switch implementations. Problem: Store files/documents Options: either store locally on the server filesystem, database or etc. Can someone help with a skeleton structure of the class, and how I would call it? I am not using an IoC, and don't really want to just yet. I just want the flexibility where I would make maybe 1 code change in the factory to call another implementation.

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