[英]Why is copy constructor called in this case?
我有两个简单的类:信用卡和帐户
#pragma once
#include<string>
class CreditCard
{
private:
std::string number;
int expMonth;
int expYear;
int pin;
public:
CreditCard():number(""), expMonth(0), expYear(0), pin(0)
{
}
CreditCard(std::string number, int expMonth, int expYear,int pin):number(number), expMonth(expMonth), expYear(expYear), pin(pin)
{
if(number.length()!=5)
{
throw std::invalid_argument("Card number must be 5 characters");
}
if(expMonth<0 || expMonth>12)
{
throw std::invalid_argument("Invalid expiration month");
}
if(expYear<2014 || expYear>2020)
{
throw std::invalid_argument("Invalid expiration year");
}
if(pin<1000 || pin>9999)
{
throw std::invalid_argument("PIN must be between 1000 and 9999");
}
}
CreditCard(const CreditCard &creditCard):number(creditCard.number), expMonth(creditCard.expMonth), expYear(creditCard.expYear), pin(creditCard.pin)
{
}
CreditCard(CreditCard &&creditCard):number(std::move(creditCard.number)), expMonth(std::move(creditCard.expMonth)), expYear(std::move(creditCard.expYear)), pin(std::move(creditCard.pin))
{
creditCard.number="";
creditCard.expMonth=0;
creditCard.expYear=0;
creditCard.pin=0;
}
CreditCard& operator = (const CreditCard &creditCard)
{
number=creditCard.number;
expMonth=creditCard.expMonth;
expYear=creditCard.expYear;
pin=creditCard.pin;
return *this;
}
CreditCard& operator = (CreditCard &&creditCard)
{
if(this!=&creditCard)
{
number=std::move(creditCard.number);
expMonth=std::move(creditCard.expMonth);
expYear=std::move(creditCard.expYear);
pin=std::move(creditCard.pin);
number=creditCard.number;
expMonth=creditCard.expMonth;
expYear=creditCard.expYear;
pin=creditCard.pin;
}
return *this;
}
std::string getNumber() const
{
return number;
}
int getExpMonth() const
{
return expMonth;
}
int getExpYear() const
{
return expYear;
}
int getPin() const
{
return pin;
}
};
#pragma once
#include<string>
#include"CreditCard.h"
class Account
{
private:
std::string number;
float amount;
CreditCard creditCard;
public:
Account():number(""), amount(0), creditCard()
{
}
Account(std::string number, float amount, CreditCard creditCard) : number(number), amount(amount), creditCard(creditCard)
{
}
Account(const Account &account) : number(account.number), amount(account.amount), creditCard(account.creditCard)
{
}
Account(Account &&account) : number(std::move(account.number)), amount(std::move(account.amount)), creditCard(std::move(creditCard))
{
}
Account& operator = (const Account &account)
{
number=account.number;
amount=account.amount;
creditCard=account.creditCard;
return *this;
}
Account& operator = (Account &&account)
{
if(this!=&account)
{
number=account.number;
amount=account.amount;
creditCard=account.creditCard;
account.number="";
account.amount=0;
account.creditCard=CreditCard("",0,0,0);
}
return *this;
}
std::string getNumber() const
{
return number;
}
float getAmount() const
{
return amount;
}
void deposit(const float &depositAmount)
{
amount+=depositAmount;
}
void withdraw(const float &withdrawAmount)
{
amount-=withdrawAmount;
}
};
总的来说,我有这行:
Account account1("x12345x",1235.2, CreditCard("12345",1,2014,1122));
怎么了:
我不明白为什么会发生4。 为什么要复制构造函数调用?
PS:对这些类别的任何更正均表示赞赏。
我不明白为什么会发生4。 为什么要复制构造函数调用?
因为这行:
Account(std::string number, float amount, CreditCard creditCard)
:
number(number), amount(amount), creditCard(creditCard)
// ^^^^^^^^^^^^^^^^^^^^^^
{ ... }
在Account
的构造函数中,您creditCard
左值creditCard
复制到成员变量creditCard
。 这将导致对CreditCard
的副本构造函数的调用。
实际上,由于您是按值使用creditCard
,因此可以安全地移动它:
Account(std::string number, float amount, CreditCard creditCard)
:
number(number), amount(amount), creditCard(std::move(creditCard))
// ^^^^^^^^^^^^^^^^^^^^^
{ ... }
这将导致对CreditCard
的move构造函数而不是步骤4中的副本构造函数的调用。
CreditCard("12345", 1, 2014, 1122)
。 我们称它为c1
。 c1
被移到Account
构造函数的creditCard
参数中。 account1
。 account1.creditCard
是根据成员初始化程序列表从构造函数参数creditCard
复制构造的。
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.