关于析构函数的调用

//stock1.h--------stock class declaration with constructions destructior added
#ifndef STOCK1_H_
#define STOCK1_H_



class Stock
{
private:
    char company[30];
    int shares;
    double share_val;
    double total_val;
    void set_tol()
    {
        total_val=share_val*shares;
    }
public:
    Stock();
    Stock(char *co,int n=0,double pr=0.0);
    ~Stock();
    void buy(int num,double price);
    void sell(int num,double price);
    void update(double price);
    void show()const;
    const Stock &topval(const Stock &s)const;
};

#endif

#include <iostream>
#include "stock.h"



//constructors
Stock::Stock()
{
    std::cout<<"Default constructor called"<<std::endl;
    std::strcpy(company,"no name");
    shares=0;
    share_val=0.0;
    total_val=0.0;
}

Stock::Stock(char *co,int n,double pr)
{
    std::cout<<"Constructor using "<<co<<" called"<<std::endl;
    std::strncpy(company,co,29);
    company[29]='\0';
    if(n<0)
    {
        std::cerr<<"Number of shares can't be negative. "<<company<<" shares set to 0"<<std::endl;
        shares=0;
    }
    else
    {
        shares=n;
    }
        share_val=pr;
        set_tol();
}

//destructor
Stock::~Stock()
{
    std::cout<<" Bye, "<<company<<"!"<<std::endl;
    system("pause");
}

void Stock::buy(int num,double price)
{
    if(num<0)
    {
        std::cerr<<"Numbers of shares purchased can't be negtive. Transaction is aborted. "<<std::endl;
    }
    else
    {
        shares+=num;
        share_val=price;
        set_tol();
    }
}

void Stock::sell(int num,double price)
{
    if(num<0)
    {
        std::cerr<<"Number of shares to be sold can't be negative. Transaction is aborted. "<<std::endl;
    }
    else if(num>shares)
    {
        std::cerr<<"you can't sell more than you have! Transaction is aborted. "<<std::endl;
    }
    else
    {
        shares-=num;
        share_val=price;
        set_tol();
    }
}

void Stock::update(double price)
{
    share_val=price;
    set_tol();
}

void Stock::show()const
{
    std::cout<<"Company: "<<company<<" Shares: "<<shares<<std::endl;
    std::cout<<"Share Price: $"<<share_val<<" Total worth: $"<<total_val<<std::endl;
}

const Stock &Stock::topval(const Stock &s)const
{
      if(s.total_val>total_val)
                  return s;
      else
                  return *this;
}