C++ 对象数组

对象数组用于创建同一个类的多个对象。声明对象数组的方法与声明标准类陷阱数组相同。以Stock类为例：

class Stock
{
private:
	std::string company;
	int shares;
	double share_val;
	double total_val;
	void set_tot(){return total_val = shares * share_val;}
public:
	Stock();
	Stock(const std::string & c0, int 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;
};

Stock mystuff[4];//创建一个包含4个Stock对象的数组mystuff

上述创建对象数组的方式未显式初始化类对象，则调用默认构造函数。若要给对象数组的每个元素进行初始化，创建对象数组方式如下：

const int STKS = 10;
Stock stocks[STKS] = {
	Stock("NanoSmart', 12.5, 20),
	Stock(),
	Stock("Monolithic Obelisks", 130, 3.25),
	Stock("Fleep Enterprises", 60, 6.5)
};

对象数组初始化：用括号括起来、以逗号分隔的值列表，每次构造函数调用表示一个数组元素的值。初始化对象数组的方案是，首先使用默认构造函数创建数组元素，然后花括号中的构造函数将创建临时对象，然后将临时对象的内容复制到相应的元素中。

示例程序：将4个数组元素进行初始化，显式它们的内容，并找出这些元素中total_val最高的一个。
1、头文件

//stock20.h--augmented version
#pragma once
#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 & c0, int 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;
};

2、实现文件

//stock20.cpp--augement version
#include "stock20.h"
#include <iostream>
Stock::Stock()
{
	company = "no name";
	shares = 0;
	share_val = 0.0;
	total_val = 0.0;
}
Stock::Stock(const std::string& co, int n, double pr)
{
	company = co; 
	if (n < 0)
	{
		std::cout << "Number of shares can't be negative;"
			<< company << " shares set to 0.\n";
		shares = 0;
	}
	else
		shares = n;
	share_val = pr;
	set_tot();
}
Stock::~Stock()
{
}
void Stock::buy(long num, double price)
{
	if (num < 0)
	{
		std::cout << "Number of shares purchased can't be nagative." << "Transacyion is aborted.\n";
	}
	else
	{
		shares += num;
		share_val = price;
		set_tot();
	}
}
void Stock::sell(long num, double price)
{
	using std::cout;
	if (num < 0)
	{
		cout << "Number of shares sold can't be nagative."
			<< "Transaction is abored.\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()const
{
	using std::cout;
	using std::ios_base;
	//set format #.###
	ios_base::fmtflags orig = cout.setf(ios_base::fixed, ios_base::floatfield);
	std::streamsize prec = cout.precision(3);

	cout << "Company: " << company << " Shares: " << shares << '\n';
	cout << "Shares Price:$" << share_val;
	//set format to #.##
	cout.precision(2);
	cout << " Total Worth:$" << total_val << '\n';
	//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;
}

3、使用文件

//usestock2.cpp-- using the Stock class
//compilewith stock20.cpp
#include <iostream>
#include "stock20.h"

const int STKS = 4;
int main()
{
	Stock stocks[STKS] = {
		Stock("NanoSmart", 12, 20.0),
		Stock("Boffo Objects", 200, 2.0),
		Stock("Monolithic Oblisks", 130, 3.25),
		Stock("Fleep Enterprises", 60, 6.5)
	};

	std::cout << "Stock holding:\n";
	int st;
	for (st = 0; st < STKS; st++)
	{
		stocks[st].show();
	}

	//set pointer to first element
	const Stock* top = &stocks[0];
	for (st = 0; st < STKS; st++)
		top = &top->topval(stocks[st]);

	//now top points to the most valuable holding
	std::cout << "\nMost valuable holding:\n";
	top->show();

	return 0;
}