对象数组
- 定义 CDate 类的对象数组 CDate dt[20]
- 只能逐个引用数组元素，即每次只能引用一个对象
- 如果有特定需要，记得要初始化
#include <iostream> #include <cstring> using namespace std; class CDate { private: int m_year, m_month, m_day; public: CDate(int year=1970, int month=1, int day=1); void Display(); }; CDate::CDate(int year, int month, int day) { cout << "Constructor called." << endl; m_year = year; m_month = month; m_day = day; } void CDate::Display() { cout << "Year: " << m_year << endl; cout << "Month: " << m_month << endl; cout << "Day: " << m_day << endl; } int main() { CDate array[3]= { CDate(2021, 1, 1), CDate(2021, 2, 2), }; for (int i = 0; i < 3; i++) { array[i].Display(); } return 0; }
对象指针
- 存放同类对象地址的指针变量
int main() { CDate array[3]= { CDate(2021, 1, 1), CDate(2021, 2, 2), }; CDate *p = array; for (; p < array + 3; p++) { p->Display(); //两种方式都能得到正确的结果 (*p).Display(); } return 0; }
综合示例
#include <iostream> using namespace std; class CDate { private: int Date_Year, Date_Month, Date_Day; public: CDate(int y=2019, int m=1, int d=1); CDate(const CDate& date); void Display(); ~CDate(); }; CDate::CDate(int y, int m, int d): Date_Year(y), Date_Month(m), Date_Day(d) { cout << "Constructor called" << endl; } CDate::CDate(const CDate& date) { cout << "Copy constructor called" << endl; Date_Year = date.Date_Year; Date_Month = date.Date_Month; Date_Day = date.Date_Day+1; } void CDate::Display() { cout << Date_Year << "-" << Date_Month << "-" << Date_Day << endl; } CDate fun(CDate date) { CDate new_date(date); return new_date; } CDate::~CDate() { cout << "Destructor called" << endl; } int main() { CDate *q = new CDate(2020, 1, 1); cout <<"动态对象>>"; q->Display(); delete q; q = new CDate[3]; q[0] = CDate(2019, 4, 1); q[1] = CDate(2019, 5, 1); for (int i = 0; i < 3; i++) { q[i].Display(); } delete[] q; //一定要记得释放 //注意动态数组的释放格式 return 0; }
q[0] 和 q[1] 两处的赋值是通过生成无名对象来赋值
赋值之后有析构无名函数的步骤
对象引用
- 不再另外占用内存
- 与其代表的对象共享同一个单元
- 对象引用必须在定义时初始化
CDate DateA(2019, 3, 13); CDate DateB(2019, 5, 1); CDate &pDate = DateA; void f() { DateA.Display(); DateB.Display(); pDate.Display(); } int main() { cout<<"原始DataA、DataB、pDate的值："<<endl; f(); pDate = DateB; cout<<"修改后DataA、DataB、pDate的值：" << endl; f(); pDate =CDate(2019, 7, 1); cout<<"修改后DataA、DataB、pDate的值：" << endl; f(); return 0; }
前两个 Constructor called 和后两个 Destructor called 都是由于第一、二两行的调用
对象参数
对象作为函数参数
- 用实参对象初始化形参对象
- 复制构造函数调用
- 单向值传递
void CDate::ModifyDate(int y, int m, int d) { Date_Year=y; Date_Month=m; Date_Day=d; } /*----------------------------------------------*/ void f(CDate DateVar) { DateVar.ModifyDate(2020, 2, 2); cout << "After modification: "; DateVar.Display(); } int main() { CDate DateA; DateA.Display(); f(DateA); //f() 退出时，生命周期结束，调用析构函数 cout << "After function call: "; DateA.Display(); return 0; }
对象指针作为函数参数
- 仅将对象地址传给函数参数，提高效率，读写方便
- 单向传地址
- 不产生新对象，不调用复制构造函数
void f(CDate *pdate) { pdate->ModifyDate(2020, 2, 2); pdate->Display(); } int main() { CDate DateA(2019); DateA.Display(); f(&DateA); cout << "After function call: "; DateA.Display(); return 0; }
没有复制构造函数的调用
f() 函数调用结束之后也没有析构函数的调用
但 f() 函数的参数必须要带 &
使用指针不仅可以访问，还可以修改实参的值
对象引用作为函数参数
- 可以使函数的调用作为左值使用
#include <iostream> using namespace std; class CDate { private: int Date_Year, Date_Month, Date_Day; public: CDate(int y=2019, int m=1, int d=1); void Display(); ~CDate(); void ModifyDate(int y, int m, int d); }; CDate::CDate(int y, int m, int d) { cout << "Constructor called" << endl; Date_Year = y; Date_Month = m; Date_Day = d; } void CDate::Display() { cout << Date_Year << "-" << Date_Month << "-" << Date_Day << endl; } CDate::~CDate() { cout << "Destructor called" << endl; } void CDate::ModifyDate(int y, int m, int d) { Date_Year=y; Date_Month=m; Date_Day=d; } CDate &fun(CDate &pdate) { pdate.ModifyDate(2020, 2, 2); cout << "引用pdata>>"; pdate.Display(); return pdate; } int main() { CDate DateA(2019),tdate; cout << "起始DateA>>"; DateA.Display(); cout << "起始tdate>>"; tdate.Display(); cout<<endl; tdate = fun(DateA); cout << "修改后DateA>>"; DateA.Display(); cout << "修改后tdate>>"; tdate.Display(); cout<<endl; fun(tdate) = CDate(2021, 2, 2); cout << "左修改后DateA>>"; DateA.Display(); cout << "左修改后tdate>>"; tdate.Display(); cout<<endl; system("pause"); return 0; }
