我有一个继承自另一个类(Account)的类(SavingAccount)。不知何故,它没有正确初始化。
=============================================== =========================
class Account
{
private:
double balance;
public:
// constructor
Account()
{
balance = 0;
}
Account(double b)
{
if (b >= 0)
balance = b;
else
{
balance = 0;
cout << "Balance cannot be negative." << endl;
}
}
// destructor
~Account()
{
// nothing
}
// required functions
bool credit(double a)
{
if (a > 0)
{
balance += a;
return true;
}
else
{
cout << "Credit amount must be greater than 0." << endl;
return false;
}
}
bool debit(double a)
{
if (a > 0 && a <= balance)
{
balance -= a;
return true;
}
else if (a > balance)
{
cout << "Debit amount exceeded account balance." << endl;
return false;
}
}
double getBalance()
{
return balance;
}
void setBalance(double b)
{
balance = b;
}
};
=============================================== =========================
class SavingAccount : public Account
{
private:
double interestRate; // percentage
public:
// constructor
SavingAccount()
{
Account::Account();
interestRate = 0;
}
SavingAccount(double b, double r)
{
if (b >= 0 && r >= 0)
{
Account::Account(b);
interestRate = r;
}
else
{
Account::Account();
interestRate = 0;
cout << "Balance or rate cannot be negative." << endl;
}
}
// destructor
~SavingAccount()
{
// nothing
}
// required functions
double calculateInterest()
{
return Account::getBalance() * interestRate / 100;
}
};
=============================================== =========================
我初衷如下:
SavingAccount acctSaving(2000, 5);
当我跳进它时,acctSaving显示它的平衡为2000。但是,当它到达外面时,余额会回到0。
如果我更改此行:
Account::Account(b);
成:
setBalance(b);
它正确返回对象,余额值为2000.出了什么问题?第一种方法怎么不对?
答案 0 :(得分:3)
Account::Account(b)
并没有做你认为它做的事情。它创建一个Account
类型的未命名临时变量,用b
初始化,然后立即销毁。
你可能正在寻找的是这样的:
SavingAccount(double b, double r)
: Account(b >= 0 && r >= 0 ? b : 0) {
/* rest of code here */
}
答案 1 :(得分:2)
您不应直接调用父构造函数。但是,您可以指定在构造子项时应使用哪个父构造函数。
当您像函数调用一样直接调用父构造函数时,您将创建一个临时对象。
// constructor
SavingAccount() // Default parent constructor is called here implicitly
{
interestRate = 0;
}
SavingAccount(double b, double r): Account(b) // Specify here parent constructor if default one is useless here
{
if (b >= 0 && r >= 0)
{
interestRate = r;
}
else
{
interestRate = 0;
cout << "Balance or rate cannot be negative." << endl;
}
}