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  • Creating methods with infinite overloads ? (.NET)

    - by MarceloRamires
    In C# you can do this: foo = string.Format("{0} {1} {2} {3} ...", "aa", "bb", "cc" ...); This method Format() accepts infinite parameters, being the first one how the string should be formatted and the rest are values to be put in the string. Today I've come to a situation where I had to get a set of strings and test them, then I remembered this language functionality, but I had no clue. After a few unsuccessful web searches, I've realised it would be more prudent to just get an array, which didn't make me quite satisfied. Q: How do I make a function that accepts infinite parameters? And how do I use it ?

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  • overload == (and != , of course) operator, can I bypass == to determine whether the object is null

    - by LLS
    Hello, when I try to overload operator == and != in C#, and override Equal as recommended, I found I have no way to distinguish a normal object and null. For example, I defined a class Complex. public static bool operator ==(Complex lhs, Complex rhs) { return lhs.Equals(rhs); } public static bool operator !=(Complex lhs, Complex rhs) { return !lhs.Equals(rhs); } public override bool Equals(object obj) { if (obj is Complex) { return (((Complex)obj).Real == this.Real && ((Complex)obj).Imaginary == this.Imaginary); } else { return false; } } But when I want to use if (temp == null) When temp is really null, some exception happens. And I can't use == to determine whether the lhs is null, which will cause infinite loop. What should I do in this situation. One way I can think of is to us some thing like Class.Equal(object, object) (if it exists) to bypass the == when I do the check. What is the normal way to solve the problem?

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  • C++: How to make comparison function for char arrays?

    - by Newbie
    Is this possible? i get weird error message when i put char as the type: inline bool operator==(const char *str1, const char *str2){ // ... } Error message: error C2803: 'operator ==' must have at least one formal parameter of class type ... which i dont understand at all. I was thinking if i could directly compare stuff like: const char *str1 = "something"; const char *str2 = "something else"; const char str3[] = "lol"; // not sure if this is same as above and then compare: if(str1 == str2){ // ... } etc. But i also want it to work with: char *str = new char[100]; and: char *str = (char *)malloc(100); I am assuming every char array i use this way would end in NULL character, so the checking should be possible, but i understand it can be unsafe etc. I just want to know if this is possible to do, and how.

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  • Is it possible to supply template parameters when calling operator()?

    - by Paul
    I'd like to use a template operator() but am not sure if it's possible. Here is a simple test case that won't compile. Is there something wrong with my syntax, or is this simply not possible? struct A { template<typename T> void f() { } template<typename T> void operator()() { } }; int main() { A a; a.f<int>(); // This compiles. a.operator()<int>(); // This compiles. a<int>(); // This won't compile. return 0; }

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  • question regarding "this" pointer in c++

    - by sil3nt
    hello there, i have been given class with int variables x and y in private, and an operator overload function, class Bag{ private: int x; int y; public: Bag(); ~Bag(); //....... //.....etc }; Bag operator+ (Bag new) const{ Bag result(*this); //what does this mean? result.x += new.x; result.y += new.y; } What is the effect of having "Bag result(*this);" there?.

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  • Overload the behavior of count() when called on certain objects

    - by Tom
    In PHP 5, you can use magic methods, overload some classes, etc. In C++, you can implement functions that exist is STL as long as the argument types are different. Is there a way to do this in PHP? An example of what I'd like to do is this: class a { function a() { $this->list = array("1", "2"); } } $blah = new a(); count($blah); I would like blah to return 2. IE count the values of a specific array in the class. So in C++, the way I would do this might look like this: int count(a varName) { return count(varName->list); } Basically, I am trying to simplify data calls for a large application so I can call do this: count($object); rather than count($object->list); The list is going to be potentially a list of objects so depending on how it's used, it could be really nasty statement if someone has to do it the current way: count($object->list[0]->list[0]->list); So, can I make something similar to this: function count(a $object) { count($object->list); } I know PHP's count accepts a mixed var, so I don't know if I can override an individual type.

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  • Java: If I overwrite the .equals method, can I still test for reference equality with ==?

    - by shots fired
    I have the following situation: I need to sort trees based by height, so I made the Tree's comparable using the height attribute. However, I was also told to overwrite the equals and hashCode methods to avoid unpredictable behaviour. Still, sometimes I may want to compare the references of the roots or something along those lines using ==. Is that still possible or does the == comparison call the equals method?

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  • Returning a struct from a class method

    - by tree
    I have a header file that looks something like the following: class Model { private: struct coord { int x; int y; } xy; public: .... coord get() const { return xy; } }; And in yet another file (assume ModelObject exists): struct c { int x; int y; void operator = (c &rhs) { x = rhs.x; y = rhs.y; }; } xy; xy = ModelObject->get(); The compiler throws an error that says there is no known covnersion from coord to c. I believe it is because it doesn't know about coord type because it is declared inside of a class header. I can get around that by declaring the struct outside of the class, but I was wondering if it is possible to do the way I am, or is this generally considered bad practice

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  • Requring static class setter to be called before constructor, bad design?

    - by roverred
    I have a class, say Foo, and every instance of Foo will need and contain the same List object, myList. Since every class instance will share the same List Object, I thought it would be good to make myList static and use a static function to set myList before the constructor is called. I was wondering if this was bad, because this requires the setter to be called before the constructor? If the person doesn't, the program will crash. Alternative way would be passing myList every time.

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  • Why `A & a = a` is valid?

    - by psaghelyi
    #include <iostream> #include <assert.h> using namespace std; struct Base { Base() : m_member1(1) {} Base(const Base & other) { assert(this != &other); // this should trigger m_member1 = other.m_member1; } int m_member1; }; struct Derived { Derived(Base & base) : m_base(m_base) {} // m_base(base) Base & m_base; }; void main() { Base base; Derived derived(base); cout << derived.m_base.m_member1 << endl; // crashes here } The above example is a synthesized version of a mistyped constructor. I used reference at the class member Derived::m_base because I wanted to make sure that the member will be initialized as the constructor had called. One problem is that nor GCC nor MSVC gives me a warning at m_base(m_base). But the more serious for me is that the assert finds everything fine and the application crashes later (sometimes far away from the mistake). Question: Is there any way to indicate such mistakes?

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  • get and set for class in model - MVC 2 asp.net

    - by bergin
    Hi there, I want to improve the program so it has a proper constructor but also works with the models environment of MVC. I currently have: public void recordDocument(int order_id, string filename, string physical_path, string slug, int bytes) { ArchiveDocument doc = new ArchiveDocument(); doc.order_id = order_id; doc.filename = filename; doc.physical_path = physical_path; doc.slug = slug; doc.bytes = bytes; db.ArchiveDocuments.InsertOnSubmit(doc); } This obviously should be a constructor and should change to the leaner: public void recordDocument(ArchiveDocument doc) { db.ArchiveDocuments.InsertOnSubmit(doc); } with a get & set somewhere else - not sure of the syntax - do I create a partial class? so: creating in the somewhere repository - ArchiveDocument doc = new ArchiveDocument(order_id, idTaggedFilename, physical_path, slug, bytes); and then: namespace ordering.Models { public partial class ArchiveDocument { int order_id, string filename, string physical_path, string slug, int bytes; public archiveDocument(int order_id, string filename, string physical_path, string slug, int bytes){ this.order_id = order_id; etc } } How should I alter the code?

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  • Java: using generic wildcards with subclassing

    - by gibberish
    Say I have a class Foo, a class A and some subclass B of A. Foo accepts A and its sublclasses as the generic type. A and B both require a Foo instance in their constructor. I want A's Foo to be of type A , and B's Foo to be of type B or a superclass of B. So in effect, So I only want this: Foo<X> bar = new Foo<X>; new B(bar); to be possible if X is either A, B, or a both subclass of A and superclass of B. So far this is what I have: class Foo<? extends A>{ //construct } class A(Foo<A> bar){ //construct } class B(Foo<? super B> bar){ super(bar); //construct } The call to super(...) doesn't work, because <A> is stricter than <? super B>. Is it somehow possible to use the constructor (or avoid code duplication by another means) while enforcing these types? Edit: Foo keeps a collection of elements of the generic parameter type, and these elements and Foo have a bidirectional link. It should therefore not be possible to link an A to a Foo.

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  • C++: Construction and initialization order guarantees

    - by Helltone
    Hi, I have some doubts about construction and initialization order guarantees in C++. For instance, the following code has four classes X, Y, Z and W. The main function instantiates an object of class X. X contains an object of class Y, and derives from class Z, so both constructors will be called. Additionally, the const char* parameter passed to X's constructor will be implicitly converted to W, so W's constructor must also be called. What are the guarantees the C++ standard gives on the order of the calls to the copy constructors? Or, equivalently, this program is allowed to print? #include <iostream> class Z { public: Z() { std::cout << "Z" << std::endl; } }; class Y { public: Y() { std::cout << "Y" << std::endl; } }; class W { public: W(const char*) { std::cout << "W" << std::endl; } }; class X : public Z { public: X(const W&) { std::cout << "X" << std::endl; } private: Y y; }; int main(int, char*[]) { X x("x"); return 0; }

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  • Why would one want to use the public constructors on Boolean and similar immutable classes?

    - by Robert J. Walker
    (For the purposes of this question, let us assume that one is intentionally not using auto(un)boxing, either because one is writing pre-Java 1.5 code, or because one feels that autounboxing makes it too easy to create NullPointerExceptions.) Take Boolean, for example. The documentation for the Boolean(boolean) constructor says: Note: It is rarely appropriate to use this constructor. Unless a new instance is required, the static factory valueOf(boolean) is generally a better choice. It is likely to yield significantly better space and time performance. My question is, why would you ever want to get a new instance in the first place? It seems like things would be simpler if constructors like that were private. For example, if they were, you could write this with no danger (even if myBoolean were null): if (myBoolean == Boolean.TRUE) It'd be safe because all true Booleans would be references to Boolean.TRUE and all false Booleans would be references to Boolean.FALSE. But because the constructors are public, someone may have used them, which means that you have to write this instead: if (Boolean.TRUE.equals(myBoolean)) But where it really gets bad is when you want to check two Booleans for equality. Something like this: if (myBooleanA == myBooleanB) ...becomes this: if ( (myBooleanA == null && myBooleanB == null) || (myBooleanA == null && myBooleanA.equals(myBooleanB)) ) I can't think of any reason to have separate instances of these objects which is more compelling than not having to do the nonsense above. What say you?

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  • error: no matching function for call to ‘BSTreeNode<int, int>::BSTreeNode(int, int, NULL, NULL)’ - what's wrong?

    - by Alexander Suraphel
    error: no matching function for call to ‘BSTreeNode::BSTreeNode(int, int, NULL, NULL)’ candidates are: BSTreeNode::BSTreeNode(KF, DT&, BSTreeNode*, BSTreeNode*) [with KF = int, DT = int] here is how I used it: BSTreeNode<int, int> newNode(5,9, NULL, NULL) ; I defined it as follows: BSTreeNode(KF sKey, DT &data, BSTreeNode *lt, BSTreeNode *rt):key(sKey),dataItem(data), left(lt), right(rt){} what's wrong with using my constructor this way? i've been pulling out my hair all night please help me ASAP!!

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  • Boost singleton and restricted

    - by Ockonal
    Hello, I'm using boost singleton from thread/detail. There is in manual, that constructor should have signlature: boost::restricted. But I can't find any reference for this type in boost library. Why do I need in this and where I can find it?

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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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  • 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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  • 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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