构造函数的初始化
- 初始化列表
- Constructor body assignment

构造函数的初始化

这个问题也需要总结一下，因为最明显的方案有两种。孰好孰坏，还得看情况。题目来自于hackerrank

初始化列表

这个在开源代码里比较常见，据说效率上比较快的。因为是构造函数吗，这里就涉及到多参函数和无参函数。请看以下代码，是初始化一个Box()中的长宽高(l,b,h).

class Box{
private:
    int l, b, h;
public:
    Box() : l(0), b(0), h(0){}
    Box(int length, int breath, int height) :
    l(length),b(breath),h(height)  //  be carefully ","
    {
    }  // this is initialzer list method
    Box (const Box& obj) :
    l(obj.l), b(obj.b),h(obj.h)
    {}   // copy constructor
    int getLength() {
	   return this->l;
    }
    int getBreadth() {
           return this->b;
    }
    int getHeight() {
	   return this->h;
    }
    long long int CalculateVolume()  // 必须大数梳理
    {
            long long int result =  1LL * this->l * this->b * this->h;
            return result;
     }
};

Please note the initialized list model is :

    Box(int length, int breath, int height) :
    l(length),b(breath),h(height)  //  be carefully ","
    {
    }  // this is initialzer list method

There is copy constructor function Box(const Box& obj) The fundamental principle of copy constructor i dont understand.But we first have a glance at :

Box(int length, int breath, int height):l(length),b(breathr, h(height) {}

and l,b,h is private variables that we want to pass constructor function’s arguments.

Notes: There will be must use initialized list as below:

No default arguments in inherit relationship,more understand:

class Box() {
private:
 int m_length;
 int m_height;
public:
 Box(int length, int height) : m_length(length),m_height(height){}
} // below must use it ^_^
class red_Box: public Box{
public:
 red_Box(int length, int height, int type) :
 Box(length, height){
     ;
 } // must use initialized list
private:
 int type;
}

Const constant in class must use it

class Box() {
private:
 int m_length;
 int m_height;
public:
 Box(int length, int height) : m_length(length),m_height(height){}
} // below must use it ^_^
class red_Box: public Box{
public:
 red_Box(int length, int height, int type) :
 Box(length, height),
 TYPE(2)
 {
     // if TYPE = 4 is error
 } // must use initialized list
private:
 int type;
 const int TYPE;

containing custom data type of members
Constructor body assignment

```c Box(){ l = 0, b = 0, h = 0; } // default value is 0, maybe use below method

# 拷贝构造函数
```c
    Box (const Box& obj) :
    l(obj.l), b(obj.b),h(obj.h)
    {}   // copy constructor

the chanlleg

类内定义的问题

c++的初始化

构造函数的初始化

初始化列表

Constructor body assignment

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