我刚刚开始学习C ++课程，而且我在处理重载算术运算符时遇到了一些问题。首先，在我的头文件中，我有：
#ifndef MONEY_H
#define MONEY_H
#include <iostream>
using namespace std;
class Money{
public:
Money(int dollars, int cents);
Money(int dollars);
Money();
int getDollars() const {return dollars;};
int getCents() const {return cents;};
void setDollarsAndCents(int dollars, int cents);
double getAmount() const {return amount ;};
void setAmount(double amount);
// Define operator functions for comparison operators
friend bool operator==(const Money& firstAmount, const Money& secondAmount);
friend bool operator<(const Money& firstAmount, const Money& secondAmount);
friend bool operator>(const Money& firstAmount, const Money& secondAmount);
//Define operator functions for arithmetic operators
friend Money operator+(const Money& firstAmount, const Money& secondAmount);
friend Money operator-(const Money& firstAmount, const Money& secondAmount);
friend Money operator*(const Money& money, int n);
friend Money operator/(const Money& money, int n);
//Define the output and input operator
friend ostream& operator<<(ostream& outStream, const Money& money);
private:
int dollars, cents;
double amount;
};
#endif
然后我在一个实现文件Money.cpp
上实现了operator + #include "Money.h"
// Construct a money object with dollars and cents
Money::Money(int newDollars, int newCents)
{
dollars = newDollars;
cents = newCents;
}
// Construct a money object with JUST the dollars
Money::Money(int newDollars)
{
dollars = newDollars;
cents = 0;
}
// Construct a money object with no arguments (default amount = 0)
Money::Money()
{
amount = 0.0;
}
// Set dollars and cents
void Money::setDollarsAndCents(int newDollars, int newCents)
{
dollars = newDollars;
cents = newCents;
}
// Set monetary amount
void Money::setAmount(double newAmount)
{
//convert cents automatically if >= 100
newAmount = dollars + cents/100.0;
amount = newAmount;
}
// Test if two Money objects are equal or not
bool operator==(const Money& firstAmount, const Money& secondAmount)
{
return (firstAmount.amount == secondAmount.amount);
}
// Test if the first operand is less than the second operand
bool operator<(const Money& firstAmount, const Money& secondAmount)
{
return (firstAmount.amount < secondAmount.amount);
}
// Test if the first operand is greater than the second operand
bool operator>(const Money& firstAmount, const Money& secondAmount)
{
return (firstAmount.amount > secondAmount.amount);
}
// Add two Money objects
Money operator+(const Money& firstAmount, const Money& secondAmount)
{
//assume cents < 100
int carry = 0;
int finalCents = firstAmount.cents + secondAmount.cents;
if (finalCents >= 100){
carry += 1;
finalCents -= 100;
}
int finalDollars = firstAmount.dollars + secondAmount.dollars + carry;
return Money(finalDollars, finalCents);
}
// Subtract two Money objects
Money operator-(const Money& firstAmount, const Money& secondAmount)
{
int borrow = 0;
int finalCents = firstAmount.cents - secondAmount.cents;
if (finalCents < 0){
finalCents += 100;
borrow = 1;
}
int finalDollars = firstAmount.dollars - secondAmount.dollars - borrow;
return Money(finalDollars, finalCents);
}
// Multiply two Money objects
Money operator*(const Money& money, int n)
{
return money.amount * n;
}
// Divide two Money objects
Money operator/(const Money& money, int n)
{
int quotient = money.amount / n;
// check if there isn't a remainder
if ( quotient * n == 0)
return money.amount / n;
else // there's a remainder
return money.dollars / n + money.cents / (n * 100);
}
// Define the output operator
ostream& operator<<(ostream& outputStream, const Money& money)
{
outputStream << money.amount;
return outputStream;
}
最后，在我的TestMoney.cpp的主要方法中，我有：
#include "Money.h"
using namespace std;
int main()
{
Money m1(-35),m2(53, 35);
//Test operator == (false)
cout << "m1 == m2 = " << (m1 == m2 ? "true" : "false") << endl;
Money m3(-35),m4(35);
//Test operator < (true)
cout << "m3 < m4 = " << (m3 < m4 ? "true" : "false") << endl;
Money m5(-35),m6(53, 35);
//Test operator > (false)
cout << "m5 > 6 = " << (m5 > m6 ? "true" : "false") << endl;
Money m7(12,50),m8(25,55);
// $12.50 & $25.50 = $38.05
//Test operator +
cout << "m7 + m8 = $" << (m7 + m8) << endl;
//~ Money m9(5,75), m10(100);
//~ // $5.75 - $100 = $-94.25
//~ //Test operator -
//~ cout << "m9 - m10 = $" << m9 - m10 << endl;
//~ Money m11(25,75);
//~ int n = 5;
//~ // $25.75 * $5 = $128.75
//~ //Test operator *
//~ cout << "m11 * m12 = $" << m11 * n << endl;
//~ Money m13(115,75);
//~ n = 3;
//~ // $115.75 / $3 = $38.58333
//~ //Test operator /
//~ cout << "m13 / n = $" << m13 / n << endl;
return 0;
}
显然，我得到答案：m7 + m8 = $4.94066e-324。答案应该是38.05美元。
我已经被困在这里很长一段时间了。如果有人能够耐心地解释我搞砸了哪里会很棒。谢谢你的帮助。
答案 0 :(得分：1)
在这种情况下，您使用的构造函数重载不会设置＆＃39; amount＆＃39;。
Money::Money(int newDollars, int newCents)
{
dollars = newDollars;
cents = newCents;
}
你的operator+
Money operator+(const Money& firstAmount, const Money& secondAmount)
{
//assume cents < 100
int carry = 0;
int finalCents = firstAmount.cents + secondAmount.cents;
if (finalCents >= 100){
carry += 1;
finalCents -= 100;
}
int finalDollars = firstAmount.dollars + secondAmount.dollars + carry;
return Money(finalDollars, finalCents);
}
您的operator<<显示amount且未初始化。
您应该在所有构造函数重载中设置amount。这可能是通过让它们都调用一个在一个地方执行init的私有函数来实现的。
更好地摆脱了以2种表示形式存储价值的双重性（美元/美分和金额）。只能将它存储为一个或另一个，它将变得更加简单。
另请注意，如果您调用no args构造函数，则您的美元和美分成员变量同样未初始化。
答案 1 :(得分：0)
问题是您的operator <<输出amount成员。然而，它是未初始化的：
// Define the output operator
ostream& operator<<(ostream& outputStream, const Money& money)
{
outputStream << money.amount; // not initialized
return outputStream;
}
如果您查看cout中的main，就可以了：
(m7 + m8)
这会返回一个临时的Money对象，它将被复制构造（不是默认构造的）。复制构造函数是编译器生成的（可以，但请参阅下面的评论）。由于m7和m8已设置amount，因此您将垃圾值复制到临时Money对象，从而将垃圾值复制。
此外，由于double变量amount未初始化，您的代码调用未定义的行为，并且编译器生成的复制构造函数将垃圾双值复制到另一个double。除非操作涉及初始化变量，否则您永远不想尝试操作未初始化的浮点变量。
最重要的是，在构建对象时，您应该努力将所有成员初始化为已定义的状态。它是否使指针为NULL，是否使双精度等于0等等。您的成员变量应设置为有效状态。