数据类型转换
//static_cast
//reinterpret_cast
//涉及const 必须要用 const_cast
//dynamic_cast
//主要用于多态 依赖于虚函数
//父类
class huahua
{
public:
int hua1;
virtual void run()
{
cout << "hhhhhhh" << endl;
}
};
//子类
class xiaohua:public huahua
{
public:
int xiaohua1;
void run()
{
cout << "xxxxhhhhhhh" << endl;
}
};
void mainr1()
{
//printf("%d",10.1); //垃圾值 printf不会完成数据类型转换
//printf("%d", static_cast(10.1)); //默认转换
//int*pint = new int(1);
//char*pchar = reinterpret_cast(pint); //指针类型转换
//for (int i = 0; i < 3; i++)
//{
// cout << static_cast(*(pchar + i)) << " "<( pchar+i) <(p); // reinterpret_cast 不适用于const
int*pint = const_cast(p);
//for (size_t i = 0; i < 5; i++)
//{
// cout << pint[i] << " " << reinterpret_cast(pint + i) << endl;
//
//}
//父类指针可以经过转换访问子类对象 反之一般不安全
huahua *pfu = new huahua;
xiaohua *pzi = new xiaohua;
huahua *phua = dynamic_cast(pzi); //子类对象转换为父类指针
phua->run();
xiaohua *pxiaohua = dynamic_cast(pfu); //转换失败 会设置为null
if (pxiaohua != nullptr)
{
pxiaohua->hua1 = 10; //访问子类继承父类的对象
pxiaohua->run();
(*pxiaohua).huahua::run(); //调用子类中的父类的方法
}
cin.get();
}
delete删除一个函数
void show(int num)
{
cout << num << endl;
}
void show(char num) = delete; //删除一个函数
//函数声明=delete
// 精确匹配 删除其他参数匹配类型函数
class myclass
{
public:
//myclass() = delete; //删除构造函数
~myclass() = delete;
};
大括号处理数据
#include
void show(initializer_listlist)
{
for (auto i : list)
{
cout << i << endl;
}
}
void show(initializer_listlist)
{
for (auto i : list)
{
cout << i << endl;
}
}
int*getmem(initializer_listlist)
{
int length = list.size();
int *p = new int[length];
int*pback = p; //备份指针
for (auto i : list)
{
*(p++) = i; //循环赋值
}
return pback;
}
void mainr2()
{
show({ 1,2,3,4,5,6 });
show({"DDD","eeee","FFFFF","dddd"});
int*p = getmem({ 1,2,3,4,5,6 });
for (size_t i = 0; i < 6; i++)
{
cout << p[i] << " ";
}
cout << endl;
cin.get();
}
forward_list
#include
void mainr3()
{
forward_listlist1{ 1,2,3,4,5 };
forward_listlist2{ 1,2,3,4,5 };
//list1.push_front(10); //只能头插
list2.assign(10,19); //分配并初始化
//for (auto i : list1)
//{
// cout << i << endl;
//}
//auto it = list1.before_begin(); //链表头结点
//list1.insert_after(it, 18); //链表的插入
auto ib = list1.begin();
list1.insert_after(ib, 19);
int a[5]{ 1,2,3,4,5 };
list1.insert_after(ib, a, a + 5); //插入
list1.erase_after(++ib); //删除
list1.sort();
list2.sort();
list1.merge(list2);//归并
cout << list1.max_size() << endl; //最大
list1.reverse(); //反转
for (auto ib = list1.begin(), ie = list1.end();ib != ie;ib++)
{
cout << *ib << endl;
}
cin.get();
}
if_exits
#include
#include
//类模板
template
class Tclass
{
public:
T t;
void show(T tx)
{
cout << tx << endl;
}
};
void main()
{
//int num;
Tclass t1;
list mylist; //检测某个模板有没有根据类型实例化
_if_exists(Tclass) //如果存在 执行块语句 可以判断变量 函数 类型
{
cout << "num is" << endl;
}
_if_not_exists(Tclass)
{
cout << "num no" << endl;
}
cin.get();
}
引用包装器
void change(int &num)
{
num = 3;
}
template
void show(T t) //函数模板 改成引用
{
cout << t << endl;
t++;
}
void main()
{
double db(1);
double &rdb(db);
show(ref(db)); //ref 引用包装器 让模板识别出引用
cout << db << endl;
cin.get();
}