正确的方法来初始化向量成员变量 [英] Correct way to initialize vector member variable

问题描述

  //方法一
 class ClassName 
 {
 public：
 ClassName（）：m_vecInts（）{} 
 
 private：
 std :: vector< int> m_vecInts 
} 
 
 //方法二
 className 
 {
 public：
 ClassName（）{} // do nothing 
 
 private：
 std :: vector< int> m_vecInts; 
} 
  

问题>初始化类的向量成员变量的正确方法是什么？
我们必须初始化它吗？

解决方案

请参阅http://en.cppreference.com/w/cpp/language/default_initialization

当具有自动存储持续时间的变量在没有初始化器的情况下声明时，默认初始化在三种情况下执行：

<当基类或非静态数据时，具有动态存储持续时间的对象由未包含初始化程序的新表达式创建

默认初始化的效果是：

• 如果T是类类型，则调用默认构造函数以提供新对象的初始值。


• 如果T是数组类型，则数组的每个元素都是默认初始化的。


• 否则，什么也不做。

由于 std :: vector 一个类类型的默认构造函数被调用。因此不需要手动初始化。

// Method One
class ClassName
{
public:
    ClassName() : m_vecInts() {}

private:
    std::vector<int> m_vecInts;
}

// Method Two
class ClassName
{
public:
    ClassName() {} // do nothing

private:
    std::vector<int> m_vecInts;
}

Question> What is the correct way to initialize the vector member variable of the class? Do we have to initialize it at all?

解决方案

See http://en.cppreference.com/w/cpp/language/default_initialization

Default initialization is performed in three situations:

1. when a variable with automatic storage duration is declared with no initializer
2. when an object with dynamic storage duration is created by a new-expression without an initializer
3. when a base class or a non-static data member is not mentioned in a constructor initializer list and that constructor is called.

The effects of default initialization are:

• If T is a class type, the default constructor is called to provide the initial value for the new object.
• If T is an array type, every element of the array is default-initialized.
• Otherwise, nothing is done.

Since std::vector is a class type its default constructor is called. So the manual initialization isn't needed.

这篇关于正确的方法来初始化向量成员变量的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！