如何使用C ++中的默认构造函数定义和声明变量？

问题描述

从我对全局范围的声明和定义的理解：

  MyClass instance（）; //声明函数返回一个MyClass 
 MyClass实例; //声明一个MyClass实例
  

声明一个变量并将其定义为在全局范围使用默认构造函数？

> Okay，因此 MyClass实例; 调用默认构造函数。任何人都可以解释这与此示例 a>：

  int a; //未默认构造，将有随机数据
 int b = int（）; //将初始化为零
  

解决方案

 code> MyClass实例; 
  

将调用默认构造函数（即没有参数的构造函数）。

这是违反直觉的，因为要使用参数调用重载的构造函数，您将执行以下操作：

  MyClass instance（param1，param2）; 
  

逻辑会告诉你传入一个空参数列表来调用默认构造函数，代码...

  MyClass实例
  

...看起来像是编译器的原型而不是构造一个 MyClass 对象。

struct 和 class 在C ++中，除了默认情况下 struct 有 public 并且类默认具有私人成员。

From my understanding of declarations and definitions, at the global scope:

MyClass instance();//Declares a function that returns a MyClass
MyClass instance;//Declares an instance of MyClass

Is it possible to declare a variable and define it to use the default constructor at global scope? What if I was using a structure instead of a class?

EDIT:

Okay, so MyClass instance; does call the default constructor. Can anyone explain how this is consistent with this example:

int a; // not default constructed, will have random data
int b = int(); // will be initialised to zero

解决方案

MyClass instance;

will invoke the default constructor (i.e. the constructor with no parameters).

This is counter-intuitive, because to invoke an overloaded constructor with parameters you would do the following:

MyClass instance(param1, param2);

Logic would tell you that you pass in an empty argument list to invoke the default constructor, but the following code...

MyClass instance();

...looks like a prototype to the compiler rather than the construction of a MyClass object.

There is no difference between a struct and a class in C++, except that a struct has public members by default and a class has private members by default.

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