this 指针

///方法涉及两个对象时，要使用this指针
///一般来说，所有的类方法都将this指针设置为调用它的对象的地址。
///每个成员函数（包括构造函数和析构函数）都有一个this指针，this指针
///指向调用对象，若方法需要引用整个调用对象，则可使用表达式*this,
///现在可以将*this作为调用对象的别名。
/*
const Stock & Stock::topval(const Stock & s)const
{
if(s.total_val > total_val)
return s;
else
return *this;
}
*/
///返回类型为引用意味着返回的是调用对象本身，而不是副本。

///stock20.h
#ifndef STOCK20_H_INCLUDED
#define STOCK20_H_INCLUDED

#include<string>
class Stock
{
private:
std::string company;
int shares;
double share_val;
double total_val;
void set_tot()
{
total_val = shares * share_val;
}
public:
Stock();
Stock(const std::string & co, long n = 0,double pr = 0.0);
~Stock();
void buy(long num, double price);
void sell(long num, double price);
void update(double price);
void show() const;
const Stock & topval(const Stock & s) const;
};

#endif // STOCK20_H_INCLUDED

///stock20.cpp
#include <iostream>
#include"stock20.h"
using namespace std;

Stock::Stock()
{

company = "no name";
shares = 0;
share_val = 0.0;
total_val = 0.0;
}
Stock::Stock(const string & co, long n, double pr)
{

company = co;
if(n<0)
{
cout <<"Number of shares can't be negative;"
<< company << "shares set to 0.\n";
shares = 0;
}
else
shares = n;
share_val = pr;
set_tot();
}
///class destructor
Stock::~Stock()
{
}
///other methods
void Stock::buy(long num, double price)
{
if(num<0)
{
cout <<"Number of shares purchased can't be negative;"
<< "Transaction is aborted .\n";
}
else
{
shares += num;
share_val = price;
set_tot();
}
}
void Stock::sell(long num, double price)
{
if(num<0)
{
cout << "Numbers of shares sold can't be negative;"
<< "Transaction is aborted.\n";
}
else if (num > shares)
{
cout <<"You can't sell more than you have; "
<< "Transaction is aborted.\n";
}
else
{
shares -= num;
share_val = price;
set_tot();
}
}
void Stock::update(double price)
{
share_val = price;
set_tot();
}
/*void Stock::show()
{
cout <<"Company: " << company
<< " Shares: " << shares << "\n"
<< "Shares Price: $ " << share_val
<< " Total Worth: $ " <<total_val
<< endl;
}*/
void Stock::show() const///
{
using std::cout;
using std::ios_base;
///set format to #.###
ios_base::fmtflags orig =
cout.setf(ios_base::fixed, ios_base::floatfield);
std::streamsize prec = cout.precision(3);
cout <<"Company: " << company
<< " Shares: " << shares << "\n"
<< "Shares Price: $ " << share_val;
///set format to #.##
cout.precision(2);
cout << " Total Worth: $ " <<total_val<< endl;
///restore original format
cout.setf(orig, ios_base::floatfield);
cout.precision(prec);
}
const Stock & Stock::topval(const Stock & s)const
{
if(s.total_val > total_val)
return s;
else
return *this;
}

///usestock20.cpp
#include<iostream>
#include"stock20.h"

const int STKS = 4;
int main()
{
Stock stocks[STKS] =
{
Stock("NanoSmart", 12, 20.00);
Stock("Boffo Objects", 200, 2.0);
Stock("Moonlight", 130, 3.25);
Stock("oppa", 183,26.0);
};
cout << "Stock holdings:\n";
int st;
for(st = 0; st < STKS; st++)
stocks[st].show();
const Stock * top = &stocks[0];
for(st=1; st<STKS; st++)
top = &top->topval(stocks[st]);
cout << "\nMost valuable holding:\n";
top->show();
return 0;

}