constructor

问题 I noticed that when you declare an array, the default constructor must be needed. Is that right? Is there any exception? For example, struct Foo{ Foo(int i ) {} }; int main () { Foo f[5]; return 0; } The code above does not compile. 回答1: Other answers are all right but, for completeness: You could also use the array initialization syntax: Foo f[5] = {1,2,3,4,5}; This works if Foo's ctor is not explicit. If it was, you'd have to be.... explicit: Foo f[5] = {Foo(1), Foo(2), Foo(3), Foo(4), Foo

问题 I expected this to work struct Parent { Parent (); Parent (const Parent &); }; struct Child : public Parent { using Parent::Parent; }; Parent p; Child c (p); Child inherits all of Parent 's constructors, right? Including Parent::Parent(const Parent &) ? x.cpp:15:11: error: no matching function for call to ‘Child::Child(Parent&)’ Child c (p); ^ x.cpp:5:2: note: candidate: Parent::Parent(const Parent&) Parent (const Parent &); ^~~~~~ x.cpp:10:16: note: inherited here using Parent::Parent; ^~~~~

问题 I need to create a Bar object, which has a private object Foo f . However, the value of Foo object parameter should be passed by the specific method int genValue() . If I initialize f in the constructor scope Bar(){...} , the compiler yell error, something like there is no constructor Foo() . If I construct like this Bar(): f(genValue()) , the compiler yells the error: test.cpp: In constructor ‘Bar::Bar()’: test.cpp:16:19: error: cannot bind non-const lvalue reference of type ‘int&’ to an

问题 Title says it all. I see it (with its corresponding end) spits out the following... new Foo( ) ...but I don't understand what the new actually does when deserializing. The docs just say it writes a Json constructor, but not what a Json constructor is ! 回答1: This method was introduced as part of an enhancement to allow Json.NET to parse date literals when represented with JavaScript constructors like so: new Date(1234656000000). For details, see Serializing Dates in JSON. Even though this

问题 I was witnessing some unexpected behavior in a C++ application I am writing in Linux Ubuntu. I would construct an object with parameters and then put a copy of that object into a std::map using the assignment operator. I wrote a simple program to demonstrate this situation... #include <iostream> #include <string> #include <map> using namespace std; class Foo { public: Foo(void) : _x(0) { cout << "Default" << endl; } Foo(int a) : _x(a) { cout << "Param" << endl; } Foo(Foo const &foo) : _x(foo.

问题 Closed. This question is off-topic. It is not currently accepting answers. Want to improve this question? Update the question so it's on-topic for Stack Overflow. Closed 3 years ago . I have a class called teacher class Teacher { private: int ID; string qualification; double salary; Date DOB; Date dateJoined; public: Teacher(); void setTeacher (int, string, double); string getQualification(); void displayTeacher(); } //This is my constructor Teacher::Teacher() { ID = 0; qualification =" " ;

问题 Is it possible to create an instance of a child object using the parent's constructor and passing it some kind of parameter (a string, in this case) to tell it the type of child that should be created? 回答1: No. In C#, you create an instance of a class, then the runtime calls its constructor. By the time the constructor executes it's too late to pick another type. However, a derived class' constructor always calls one of its base class' constructors, and you can use that to your advantage (to

问题 Lets say I have a class holding some members of some type. I know that the syntax for try-catch blocks with initializer lists is as follows template<int N> struct Member { Member() { std::cout << "Default constructor of Member " << N << std::endl; } }; class A { Member<1> m1; Member<2> m2; // n members public: A() try : m1() , m2() { // constructor implementation } catch (std::exception const & e) { // ... cleanup throw; // and rethrow } }; Since the initializer list is involved I can't use

问题 // In A.h class A { public: enum eMyEnum{ eOne, eTwo, eThree }; public: A(eMyEnum e); } // In B.h #include "A.h" class B { B(); private: A memberA; } // In B.cpp #include "B.h" B::B(void) : memberA(A::eOne) {} The declaration to 'memberA' gives me a compile error using the g++ compiler: error: 'A::eOne' is not a type How can I overcome this? Do I simply need to create a default constructor that takes no parameters? 回答1: It sounds like you are trying to initialise a member variable. You could

问题 I'm trying to unit test a class with 2 constructors. Each constructor has multiple parameters that set public properties. My question is, should I have only 2 unit tests with multiple asserts to check that each property was set OR a test for each parameter for each constructor? Public Person(string name, string phone, string birthday) { name = name; phone = phone; birthday = birthday; } Public Person(string name) : this(name, null, null) {} 回答1: The operation that you are testing is that the