对象与变量

【1】对象与变量

变量是变量，对象归对象。二者不可混为一谈（许多资料书把两者没有明确区分）。

个人认为，由类直接创建的称为对象。由内部数据类型定义的称为变量。

另外，一个对象包含许多成员变量和成员函数。

下面就对象与变量的对比实现示例代码如下：

#include<iostream>
using namespace std;

/*
 *自定义整型类
 */
class Int
{
private:
    int num;

public:
    Int(int x = 0):num(x)  //默认复合构造函数
    {
        cout<<"Create Int: "<<this<<endl;
    }
    Int(const Int &it):num(it.num)   //拷贝构造函数
    {
        cout<<"Copy Int object: "<<this<<endl;
    }
    Int & operator=(const Int &it)  //赋值函数
    {
        cout<<"operator =  "<<this<<endl;
        if(this != &it)
        {
            num = it.num;
        }
        cout<<" = "<<endl;
        return *this;
    }
    ~Int()  //析构函数
    {
        cout<<"Free Int: "<<num<<"  "<<this<<endl;
    }

public:
    Int operator++()
    //(Int * const this)(隐藏this指针)
    {
        ++num;
        return *this;
    }
    /*
     *方法1实现后置++
     */
    /*
    Int operator++(int)
    {
         Int tmp = *this;   // Int tmp(*this);
         ++num;
         return tmp;
    }
    */
    /*
     *方法2实现后置++
     */
    Int operator++(int)
    {
        return Int(num++);
    }
    /*
     *方法3实现后置++
     */
    /*
    Int operator++(int)
    {
        Int tmp = *this;
        ++*this;//(*this).operator++();this->operator++();
        return tmp;
    }
    */
    /*
     *方法4实现后置++
     */
    /*
    Int operator++(int)
    {
       Int tmp=*this;
       ++num;
       return tmp;
    }
    */
    Int operator+(const Int &it)  //重载运算符+（Int）
    //Int operator+(Int * const this, const Int &it)  参数
    {
        return Int((*this).num + it.num);
    }
    
    Int operator+(const int x)   //重载运算符+（int）
    {
        return Int(num + x);
    }
   int operator=(const int x)  //重载赋值运算符=
    {
        num = x;
        return x;
    }
    bool operator<(int x)  // 重载比较运算符<
    {
       return num < x;
    }
    void print() const     //打印
    {
        cout<<num<<endl;
    }
};
//////////////////////////////////////

void main()
{
    //隐式类型转换
     Int a = 9, b; 
     //构建a对象，隐式类型转换
     //构建b对象，复合默认构造函数。所以，对象b中成员变量num=0;
     
     //对象+变量
     int x = 10;
     b = a + x;  // == a.operator+(x) == operator(&a, x);
     b.print();  //19

     //对象 + 对象
     Int c;
     c = a + b;   //对象 + 对象
     //c = a.operator+(b);
     //c = operator(&a,b);
     //c.operator = (a.operator+(b));
     c.print();   //28

     //前置++
     Int i = 100;
     ++i;     
     //i.operator++();  
     //operator++(&i);
     Int j = 0;
     j = i++;
     i.print();  //102
     j.print();  //101


     //对象与变量对比后置++
     Int d = 1, e = 0;
     e = d++;      
     // j=i.operator++(0);
     // j.operator=(i.operator++(0));
     // j=operator++(&i,0);
     d.print(); //2
     e.print(); //1
     //m,n可以看做变量
     int m = 0, n = 0;
     m = n++;
     cout<<m<<endl; //0

     Int  f= 1,g=1;   //对象
     f + g = 12;      //可以通过OK!!!!!!//???????????

    int k = 1, l = 2;
//    k + l = 10;   //error!!不可以通过

    //变量
    int h = 10, p = 10;   //变量
    ++i = 10;
    //i++=10;     //error!!!!!!!!!

    //对象
    Int s = 0;  
    ++s = 10;
    //i.operator++();
    //operator++(&i);
    i++ = 100;

    //对象操作
    Int ai = 0, aj = 10, ak;      
    ak = ai + aj;
    ak.print();  //10
    ai = ai++ +1;
    //产生三个对象：
    //ai.operator=(ai.operator++(0).operator+(1));
    //ai.operator=(operator++(&ai,0).operator+(1));
    //operator=(&ai, (operator++(&ai,0).operator+(1)))
    // ai ,@1 @2
    ai.print();  //1
}

分析内容见代码具体备注。

【2】关于变量 i++

示例代码如下：

#include<iostream>
using namespace std;

void  main()
{
    int a = 4;
    a += (a++);
    cout<<"a :"<<a<<endl;   //9 = 5 + 4

    int b = 4;
    b += (++b);
    cout<<"b :"<<b<<endl;   //10 = 5 + 5

    int c = 4;
    (++c) += c;
    cout<<"c :"<<c<<endl;   //10 = 5 + 5

    int d = 4;  
    (++d) += (d++);     
    cout<<"d :"<<d<<endl;   //11 = 5 + 6

    int f; 
    cout<<"f :"<<(f=d)<<endl;  //11
    int m = 5;

    m *= m*m;
    cout<<"m :"<<m<<endl;    //125 = 5 * 5 * 5  

    int n = 5;
    n *= n*(n++);
    cout<<"n :"<<n<<endl;    //126 = 5 * 5 * 5 + 1

    int  h = 5;
    h *= (h++)*h;
    cout<<"h :"<<h<<endl;    //126 = 5 * 5 * 5 + 1

    int k = 0; 
    ++k = h;
    cout<<"k :"<<k<<endl;    //126

    int g = 10;
    (++g) *= g*g;  
    cout<<"g :"<<g<<endl;  //1331 = 11 * 11 * 11

    int s = 10;
    s = (++s)*s*s;
    cout<<"s :"<<s<<endl;  //1331 = 11 * 11 * 11
}

/*
a :9
b :10
c :10
d :11
f :11
m :125
n :126
h :126
k :126
g :1331
s :1331
*/

具体结论自己总结。

Good Good Study, Day Day Up.

顺序  选择  循环  坚持  总结