关于析构函数和构造函数何时调用的小例子

Posted 2020-08-14 SuperHero

详情见C++ PrimerPlus第十章

省略其他函数，将构造函数和析构函数写出来

Stock::Stock() //default constructor
{
    std::cout<<"Default constructor called\n";
    company="no name";
    shares=0;
    share_val=0;
    total_val=0;
}

Stock::Stock(const std::string&co,long n,double pr)
{
    std::cout<<"Constructor using"<<co<<"called\n";
    company=co;
    if(n<0)
    {
        std::cout<<"Number of shares can‘t be negative;"<<company<<"shares set to 0.\n";

    }
    else
    {
        shares=n;
    }
    share_val=pr;
    set_tot();
}

Stock::~Stock()
{
    std::cout<<"Bye,"<<company<<"!\n";
}

正常情况下析构函数和构造函数一般没有cout语句，这里为了显示出他何时被调用，加上了输出语句。

int main()
{
    {
        using std::cout;
        cout<<"Using constructors to creat new objects\n";
        Stock stock1("NankSmart",12,20);
        stock1.show();
        Stock stock2("Boffo Objects",2,2);//调用时
        // 直接调用了构造函数 即下列函数
       
 /*Stock::Stock(const std::string&co,long n,double pr)
{
    std::cout<<"Constructor using"<<co<<"called\n";
    company=co;
    if(n<0)
    {
        std::cout<<"Number of shares can‘t be negative;"<<company<<"shares set to 0.\n";

    }
    else
    {
        shares=n;
    }
    share_val=pr;
    set_tot();
}
  因此编译后有如下语句：
  Constructor usingBoffo Objectscalled
  Company: Boffo Objects shares: 2
  Share price: 2.000 total worth :4.00
         * */
        
　　　　　stock2.show();

        cout<<"Assigning stock1 to stock2 :\n";
        stock2=stock1;
        cout<<"Listening stock1 and stock2: \n";
        stock1.show();
        stock2.show();

        cout<<"Using a constructor to reset an object\n";
        stock1=Stock("Nifty Foods",10,50);
        //这里调用了析构函数，有如下语句 "Bye,Nifty Foods!"
        cout<<"Revised stock1:\n";
        stock1.show();
        cout<<"Done\n";
        //最后结束的时候，全部对象结束调用，所以有调用了两个对象的析构函数
        //有如下语句
        //Bye,NankSmart!
        //Bye,Nifty Foods!
    }
}
最后是编译后的结果（有些遍以前可能不同）

Using constructors to creat new objects
Constructor usingNankSmartcalled
Company: NankSmart shares: 12
Share price: 20.000 total worth :240.00
Constructor usingBoffo Objectscalled
Company: Boffo Objects shares: 2
Share price: 2.000 total worth :4.00
Assigning stock1 to stock2 :
Listening stock1 and stock2:
Company: NankSmart shares: 12
Share price: 20.000 total worth :240.00
Company: NankSmart shares: 12
Share price: 20.000 total worth :240.00
Using a constructor to reset an object
Constructor usingNifty Foodscalled
Bye,Nifty Foods!
Revised stock1:
Company: Nifty Foods shares: 10
Share price: 50.000 total worth :500.00
Done
Bye,NankSmart!
Bye,Nifty Foods!

Process finished with exit code 0