constructor

问题 Which method below is best to define a constructor prototype and why? Method 1: MyConstructor.prototype.myFunction1 = function(){}; MyConstructor.prototype.myFunction2 = function(){}; Method 2: MyConstructor.prototype = { myFunction1: function(){}, myFunction2: function(){} }; I'm mostly concerned about speed. Thanks! 回答1: I would say there wouldn't be much of a difference. Using an object literal to assign to the Object.prototype is something you can't do if you're assigning the prototype

问题 I don't understand why in this constructor declaration, the input parameter is assigned 2. What does it mean? Does it mean that by default (unless something else is passed), size will be 2? Graph(int size = 2); I've never seen syntax like this, so I don't even know how to Google it :/ Thanks in advance! 回答1: You're right, the parameter value will be 2 by default. So you can call it normally: Graph g(5); in which case size will be equal to 5, or you can call it without providing a value: Graph

问题 I need to add into the list one object CompanyDetails, so I get data from my database, and load it into constructor. result.Add(new CompanyDetails() { Name = dr["name"].ToString(), City = dr["city"].ToString(), StreetName = dr["streetName"].ToString(), StreetNr = Convert.ToInt32(dr["apartmentNr"]), Tax = int.Parse(dr["TAX"].ToString() )}); StreetNr and Tax can have null value. And when I'm trying to run it i get the error: Object cannot be cast from DBNull to other types How can I fix it? I

问题 It seems that a constructor that takes a non-const reference to an istream cannot be constructed with a temporary value in C++. #include <iostream> #include <sstream> using namespace std; class Bar { public: explicit Bar(std::istream& is) {} }; int main() { istringstream stream1("bar1"); Bar bar1(stream1); // OK on all platforms // compile error on linux, Mac gcc; OK on Windows MSVC Bar bar2(istringstream("bar2")); return 0; } This compiles fine with MSVC, but not with gcc. Using gcc I get a

问题 It seems that a constructor that takes a non-const reference to an istream cannot be constructed with a temporary value in C++. #include <iostream> #include <sstream> using namespace std; class Bar { public: explicit Bar(std::istream& is) {} }; int main() { istringstream stream1("bar1"); Bar bar1(stream1); // OK on all platforms // compile error on linux, Mac gcc; OK on Windows MSVC Bar bar2(istringstream("bar2")); return 0; } This compiles fine with MSVC, but not with gcc. Using gcc I get a

问题 I suspect the prototypes of fill constructor and range constructor of std::vector (and many other STL types) given in this webpage are not right, so I implement a NaiveVector to mimic these two prototypes. My code is: #include <iostream> #include <vector> using namespace std; template <typename T> struct NaiveVector { vector<T> v; NaiveVector(size_t num, const T &val) : v(num, val) { // fill cout << "(int num, const T &val)" << endl; } template <typename InputIterator> NaiveVector

问题 I'd like the constructor of a class to automatically determine the full path to the calling function, so that that class can write a file that's guaranteed to be in the caller's directory (instead of whatever happens to be the pwd() ). So, I have the following setup: In some_path/test.m : function test SomeClass() end In some_path/some_subdir/SomeClass.m : classdef SomeClass < handle methods function obj = SomeClass() evalin('caller', 'mfilename(''fullpath'')') end end end When I call test()

问题 I've been searching for this and I'm amazed I haven't found anything. Why can't I inherit a base class constructor using using declaration and add an overload in the derived class? I'm using Visual C++ 2013, the base class constructor is ignored when default-constructing b : error C2512: 'B' : no appropriate default constructor available I've dealt with this by re-defining the constructors, but I don't like that. This is just a minimal example, it wouldn't bother me if I had only one base

问题 Well, I'm gonna be pretty straightforward here, I just have a piece of code in c++ which I'm not sure I really understand and need some help with. Ok, to simplify lets just say I have a class that is defined like this: (the real class is a little bit more complicated, but this is what matters) class myClass : public Runnable { Semaphore *m_pMySemaphore; __Queue<Requests> *m_pQueue; Request m_Request; VetorSlotBuffer *m_vetorSlotBuffer; } Up to here nothing is wrong, myClass is just a regular

问题 Pretty easy question, but anyway: is there any reason to override default constructor like this: public SomeObject(){ } It is public. It is does not have any logic. So, is there necessary? I didn't see the whole picture? Appreciate all your help. 回答1: One reason to define an empty no-arg constructor is if there is also a non-default constructor and the no-arg constructor is still desired to be accessible (public or protected). This is because any [other] constructor definition will prevent