constructor

问题 This question already has answers here : Closed 7 years ago . Possible Duplicate: Why does this() and super() have to be the first statement in a constructor? I'd like to have constructor chain in Java. For example, with the first constructor I have a string as a parameter, and call the second constructor as I create an object from the parameter string. public class IMethodFinder { public IMethodFinder(String projectName, String methodName, int numberOfParameters) { IProject project =

问题 I'm trying to practice Inheriting Constructors in C++. I have compiled and run following program in gcc and it's working fine. #include<iostream> using namespace std; class Base1 { public: Base1() { cout<<"Base1 Default Constructor\n"; } Base1(int i) { cout<<"Base1 parametrized Constructor\n"; } }; class Base2 { public: Base2() { cout<<"Base2 Default Constructor\n"; } Base2(const string& s) { cout<<"Base2 parametrized Constructor\n"; } }; class Derived :public Base1, public Base2 { public:

问题 What is the difference between this: public class Foo { private Bar bar; public Foo() { bar = new Bar(); } } and this: public class Foo { private Bar bar = new Bar(); public Foo() { } } 回答1: The difference is that in the second case field initialization happens before this/base constructor while in the first case initialization happens inside the constructor. 回答2: The CLR does not support initializing fields like this. To make it work, the C# compiler rewrites your constructor. The IL looks

问题 I have a class which represents a set of numbers. The constructor takes three arguments: startValue , endValue and stepSize . The class is responsible for holding a list containing all values between start and end value taking the stepSize into consideration. Example: startValue: 3, endValue: 1, stepSize = -1, Collection = { 3,2,1 } I am currently creating the collection and some info strings about the object in the constructor. The public members are read only info strings and the collection

问题 I have a class with an object as a member which doesn't have a default constructor. I'd like to initialize this member in the constructor, but it seems that in C++ I can't do that. Here is the class: #include <boost/asio.hpp> #include <boost/array.hpp> using boost::asio::ip::udp; template<class T> class udp_sock { public: udp_sock(std::string host, unsigned short port); private: boost::asio::io_service _io_service; udp::socket _sock; boost::array<T,256> _buf; }; template<class T> udp_sock<T>:

问题 Consider: struct A { A (int); A (const A &); }; struct B { A foo [2]; B (const A & x, const A & y) : foo {x, y} /* HERE IS THE PROBLEM */ {} }; I was expecting this to work since I'm using C++0x support in GCC4.3, which allegedly supports initialiser lists. No joy. I have a class A which has no default constructor. This is not negotiable. Assignment post-default is not an option. I am trying to create B which uses A. B::foo may not be std::vector. How can I initialise B::foo in B(...) ,

问题 Consider: struct A { A (int); A (const A &); }; struct B { A foo [2]; B (const A & x, const A & y) : foo {x, y} /* HERE IS THE PROBLEM */ {} }; I was expecting this to work since I'm using C++0x support in GCC4.3, which allegedly supports initialiser lists. No joy. I have a class A which has no default constructor. This is not negotiable. Assignment post-default is not an option. I am trying to create B which uses A. B::foo may not be std::vector. How can I initialise B::foo in B(...) ,

问题 I had a strange problem , declare a static member variable whose name is B class in A class . And initialize in the cpp file. but the constructor of B class was never called. I try to use some small test , the test constructor could be called normally. so it is very strange for our production system. The code like this , in hpp : class Test { public: Test() { ofstream file("/tmp/wup.txt",ios::app); file << "wup in test" << endl; file.close(); } }; //## An extended personality class

问题 An object of a struct/class (that has no constructor ) can be created using an initializer list . Why is this not allowed on struct/class with constructor ? struct r { int a; }; struct s { int a; s() : a(0) {} }; r = { 1 }; // works s = { 1 }; // does not work 回答1: No, an object with a constructor is no longer considered a POD (plain old data). Objects must only contain other POD types as non-static members (including basic types). A POD can have static functions and static complex data

问题 When i invoke a virtual function from a base constructor, the compiler does not give any error. But when i invoke a pure-virtual function from the base class constructor, it gives compilation error. Consider the sample program below: #include <iostream> using namespace std; class base { public: void virtual virtualfunc() = 0; //void virtual virtualfunc(); base() { virtualfunc(); } }; void base::virtualfunc() { cout << " pvf in base class\n"; } class derived : public base { public: void