C++构造函数

2019-03-08 12:01:59 阅读：204 来源： 互联网

标签：val double void 默认 C++ 构造函数 Stock

// stock10.h ?Stock class declaration with constructors, destructor added
#ifndef STOCK1_H_
#define STOCK1_H_
#include <string>
class Stock
{
private:
    std::string company;
    long shares;
    double share_val;
    double total_val;
    void set_tot() { total_val = shares * share_val; }
public:
    Stock();        // 默认构造函数
    Stock(const std::string & co, long n = 0, double pr = 0.0);
    ~Stock();       // noisy destructor
    void buy(long num, double price);
    void sell(long num, double price);
    void update(double price);
    void show();
}；
#endif

// stock1.cpp ?Stock class implementation with constructors, destructor added
#include <iostream>
#include "stock1.h"
// constructors (verbose versions)
Stock::Stock()        // default constructor
{
    std::cout << "Default constructor called\n";
    company = "no name";
    shares = 0;
    share_val = 0.0;
    total_val = 0.0;
}

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";
        shares = 0;
    }
    else
        shares = n;
    share_val = pr;
    set_tot();
}
// class destructor
Stock::~Stock()        // verbose class destructor
{
    std::cout << "Bye, " << company << "!\n";
}

// other methods
void Stock::buy(long num, double price)
{
    if (num < 0)
    {
        std::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)
{
    using std::cout;
    if (num < 0)
    {
        cout << "Number 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()
{
    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';
    cout << "  Share 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);
}
int main()
{
        Stock stock1= Stock("NanoSmart", 12, 20.0);
        stock1.show();        

        Stock Stock2("Nano", 120, 40.0);
        Stock2.show();

        Stock Stock3;
        Stock3.show();

        Stock *Stock4 = new Stock("Smart",230,230);
        Stock4->show();

    system("pause");
    return 0;
}

构造函数中有一类成为默认构造函数，默认构造函数没有参数，因此在声明中不需要对其进行赋值。
当类中没有任何构造函数时，才会去编译默认构造函数。在定义构造函数后，必须也要为类定义默认构造函数，若是未定义默认构造函数，下面代码将会出错。
Stock Stock3;

构造函数的调用提供了两种方式，第一种：显式调用构造函数：
Stock stock1= Stock("NanoSmart", 12, 20.0);
另一种隐式构造函数：
Stock Stock2("Nano", 120, 40.0);

标签：val,double,void,默认,C++,构造函数,Stock
来源： https://www.cnblogs.com/almn/p/10494929.html

本站声明： 1. iCode9 技术分享网（下文简称本站）提供的所有内容，仅供技术学习、探讨和分享；
2. 关于本站的所有留言、评论、转载及引用，纯属内容发起人的个人观点，与本站观点和立场无关；
3. 关于本站的所有言论和文字，纯属内容发起人的个人观点，与本站观点和立场无关；
4. 本站文章均是网友提供，不完全保证技术分享内容的完整性、准确性、时效性、风险性和版权归属；如您发现该文章侵犯了您的权益，可联系我们第一时间进行删除；
5. 本站为非盈利性的个人网站，所有内容不会用来进行牟利，也不会利用任何形式的广告来间接获益，纯粹是为了广大技术爱好者提供技术内容和技术思想的分享性交流网站。

ICode9

C++构造函数