c++ - 重载运算符问题 C++

Question

我遇到了一个似乎无法正常工作的重载运算符的问题。以下是我的代码。

帐户.H

#ifndef SICT_ACCOUNT_H__
#define SICT_ACCOUNT_H__

#include <iostream>

#define MAX_NAME 40

namespace sict
{
    class Account
    {
        char name_[MAX_NAME+1];
        double balance_;
    public:
        Account();
        Account(double);
        Account(const char*, double = 0.0);
        void display(bool = true) const;
        Account& operator=(const Account&);
        Account& operator+=(const Account&);
        friend Account operator+(Account&, const Account&);
    };
    std::ostream& operator<<(std::ostream& os, const Account& a);
};

#endif

帐户.CPP

 #include <cstring>
 #include <iomanip>
 #include "Account.h"

namespace sict
{
    Account::Account()
    {
        name_[0] = '\0';
        balance_ = 0;
    }

    Account::Account(double balance)
    {
        name_[0] = '\0';
        balance_ = balance;
    }

    Account::Account(const char name[], double balance)
    {
        name_[MAX_NAME] = '\0';
        strncpy(name_, name, MAX_NAME);
        balance_ = balance;
    }

    void Account::display(bool gotoNewline) const
    {
        std::cout << (name_[0] ? name_: "No Name") << ": $" << std::setprecision(2) << std::fixed << balance_;
        if(gotoNewline)
        {
          std::cout << std::endl;
        }
    }

    std::ostream& operator<<(std::ostream& os, const Account& a)
    {
      a.display();
      return os;
    }

    Account& Account::operator=(const Account& c)
    {
      balance_ = c.balance_;
      name_[MAX_NAME] = '\0';
      strncpy(name_, c.name_, MAX_NAME);

      return *this;
    }

    Account& Account::operator+=(const Account& b)
    {
      balance_ += b.balance_;
      return *this;
    }

    Account operator+(Account& a, const Account& b)
    {
      return a.balance_ + b.balance_;
    }


}

主要

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

using namespace sict;

void displayABC(const Account& a, const Account& b, const Account& c)
{
    std::cout << "A: " << a << std::endl << "B: " << b << std::endl
    << "C: " << c << std::endl << "--------" << std::endl;
}

int main()
{
    Account a;
    Account b("Saving", 10000.99);
    Account c("Checking", 100.99);
    displayABC(a, b, c);
    a = b + c;
    displayABC(a, b, c);
    a = "Joint";
    displayABC(a, b, c);
    a = b += c;
    displayABC(a, b, c);
    a = b += c += 100.01;
    displayABC(a, b, c);

    return 0;
}

我应该得到的输出是

A: No Name: $0.00
B: Saving: $10000.99
C: Checking: $100.99
--------
A: No Name: $10101.98
B: Saving: $10000.99
C: Checking: $100.99
--------
A: Joint: $10101.98
B: Saving: $10000.99
C: Checking: $100.99
--------
A: Saving: $10101.98
B: Saving: $10101.98
C: Checking: $100.99
--------
A: Saving: $10302.98
B: Saving: $10302.98
C: Checking: $201.00

这是我现在得到的结果

A: No Name: $0.00
B: Saving: $10000.99
C: Checking: $100.99
--------
A: No Name: $10101.98
B: Saving: $10000.99
C: Checking: $100.99
--------
A: Joint: $0.00
B: Saving: $10000.99
C: Checking: $100.99
--------
A: Saving: $10101.98
B: Saving: $10101.98
C: Checking: $100.99
--------
A: Saving: $10302.98
B: Saving: $10302.98
C: Checking: $201.00
--------

如您所见，显示的整数值为 0:

A: union :$0.00。

我似乎无法弄清楚这一点。任何帮助表示赞赏!

Answer 1

displayABC(a, b, c);
a = b + c;
displayABC(a, b, c);
a = "Joint"; //The Problem!!
displayABC(a, b, c);
a = b += c;
displayABC(a, b, c);
a = b += c += 100.01;
displayABC(a, b, c);

您还没有为字符串对象定义特定的 operator=，因此，编译器在 Constructor Account(const char name[], double balance = 0.0 )，因为没有指定余额，所以将余额设置为 0。

您应该将关键字 explicit 添加到构造函数以防止它这样做，或者添加一个额外的重载以允许在不改变平衡的情况下设置名称。

explicit Account::Account(const char name[], double balance)
{
    name_[MAX_NAME] = '\0';
    strncpy(name_, name, MAX_NAME);
    balance_ = balance;
}

顺便说一下，在 C++ 世界中，您应该将 const char * 类型的所有引用替换为 std::string，并将其存储在您的对象中.唯一应该使用 c 字符串的情况是必须与 c 库交互时。