constructor

问题 The draft book Effective C++11 by Scott Meyers states: Distinguish () and {} when creating objects What's the difference between Object obj(args...) and Object obj{args...} ? and why Scott says so. Update: The question How to use C++11 uniform initialization syntax? asks for HOW, and this question asks for WHY. Update2: I find the following link is helpful and completely answers this question: https://softwareengineering.stackexchange.com/questions/133688/is-c11-uniform-initialization-a

问题 I have been reading Effective Java by Joshua Bloch and so far it really lives up to its reputation. The very first item makes a convincing case for static factory methods over constructors . So much that I began to question the validity of the good old constructors :). The advantages/disadvantages from the book are summarized below: Advantages: They have names! We have total instance control (Singletons, performance, etc.) They can return a subtype/interface Compiler can provide type

问题 Is the following legal according to the C++11 standard ( = default outside the definition of the class) ? // In header file class Test { public: Test(); ~Test(); }; // In cpp file Test::Test() = default; Test::~Test() = default; 回答1: Yes, a special member function can be default-defined out-of-line in a .cpp file. Realize that by doing so, some of the properties of an inline-defaulted function will not apply to your class. For example, if your copy constructor is default-defined out-of-line,

问题 I know that there is no return type of the constructors in C++ However, the code below compiles right. What is returned by the constructor in the code below? class A{ public: A() {} } A a = A(); //what is returned by A() here, why? Is there any conflict here? 回答1: Nothing is returned from the constructor. The syntax A() is not a constructor call, it creates a temporary object of type A (and calls the constructor in the process). You can't call a constructor directly, constructors are called

问题 I am extending one of the SPL (Standard PHP Library) classes and I am unable to call the parent's constructor. Here is the error I am getting: Fatal error: Cannot call constructor Here is a link to the SplQueue 's documentation: http://www.php.net/manual/en/class.splqueue.php Here is my code: $queue = new Queue(); class Queue extends SplQueue { public function __construct() { echo 'before'; parent::__construct(); echo 'I have made it after the parent constructor call'; } } exit; What could

问题 So I was working on my code, which is designed in a modular way. Now, one of my classes; called Splash has to create a object of another class which is called Emitter . Normally you would just create the object and be done with it, but that doesn't work here, as the Emitter class has a custom constructor. But when I try to create an object, it doesn't work. As an example; Emitter has a constructor like so: Emitter::Emitter(int x, int y, int amount); and needs to be created so it can be

问题 I have a templated class A<T, int> and two typedefs A<string, 20> and A<string, 30>. How do I override the constructor for A<string, 20> ? The following does not work: template <typename T, int M> class A; typedef A<std::string, 20> one_type; typedef A<std::string, 30> second_type; template <typename T, int M> class A { public: A(int m) {test= (m>M);} bool test; }; template<> one_type::one_type() { cerr << "One type" << endl;} I would like the class A<std::string,20> to do something that the

问题 As it currently stands, this question is not a good fit for our Q&A format. We expect answers to be supported by facts, references, or expertise, but this question will likely solicit debate, arguments, polling, or extended discussion. If you feel that this question can be improved and possibly reopened, visit the help center for guidance. Closed 8 years ago . Why can't I use code like this? <?php class NoConstructor { } class ChildWithConstructor extends NoConstructor { public function _

问题 When using @Autowired (not xml configuration), could someone compare the set/constructor binding advantages and disadvantages? See the following examples: public class Example{ private Logger log; // constructor wiring @Autowired public Example(Logger log){ this.log = log; } } public class Example{ // setter wiring @Autowired private Logger log; } 回答1: It is entirely a matter of preference. Spring frowns upon constructor injection, or at least used to, because thus circular dependencies

问题 The following code gives a compilation error: class parent { parent(int a){} } class child extends parent{} Error: Main.java:6: cannot find symbol symbol : constructor parent() location: class parent class child extends parent{} ^ 1 error I was trying to do different things and found that adding a return type to the parent constructor got rid of the error!!! class parent { int parent(int a){} } class child extends parent{} I've read that constructors should not have return type, which clearly