[C++知识库]C++基础知识学习总结2

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类入门

#include <iostream>
#include <string>
using namespace std;
class Dog;//声明
class Cat
{
    friend istream &read(istream &, Cat &item);
    //class定义类时,访问修饰符之前默认是private
public:
    Cat() = default;
    Cat(const int &a) : Age(a) {}
    Cat(const int &a, const string &s) : Age(a), Name(s) {}
    Cat(istream &is);
    int age() const //const 常函数
    {
        //隐式内联,声明、定义都在类里面
        access_num++;
        return this->Age;
    }
    int sex() const
    {
        access_num++;
        return this->Sex;
    }
    string name() const
    {
        return this->Name;
    }
    Cat& setName(string name);
    Cat& setAge(const int age);
    void inlineTest();
    inline void inlineTest2();
private:
    int Sex = 1; 
    int Age;
    string Name;
    mutable size_t access_num;//mutable修饰,在const函数里面也可以被修改
};
Cat::Cat(istream &is)
{
    read(is, *this);
}
inline void Cat::inlineTest()
{
    cout << "内联方式2:类中声明不加inline,类外定义加inline" << endl;
}
void Cat::inlineTest2()
{
    cout << "内联方式3:只在类中声明加inline" << endl;
}
Cat& Cat::setName(string name)
{
    Name = name;
    return *this;
}
Cat& Cat::setAge(int age)
{
    Age = age;
    return *this;
}
//类外部的函数想可访问类内的私有属性,以定义友元
istream &read(istream &is, Cat &item)
{
    //友元函数  可以访问私有属性 Sex
    is >> item.Age >> item.Name >> item.Sex;
    return is;
}
ostream &print(ostream &os, const Cat &item)
{
    os << "名称:" << item.name() << "\t年龄:" << item.age();
    return os;
}
int main()
{
    Cat c;
    print(cout, c.setName("千任雪").setAge(18));
    c.inlineTest();
    cout << c.sex() << endl;
    return 0;
}

作用域

int big;
class Scope
{
   public:
     typedef string::size_type index;
     index test(index a, int big) const;

   private:
     int Age;
     int big;
};
Scope::index Scope::test(index a, int big) const {
   //int t = big;//是入参 big
   //int t = this->big; //类变量big
   int t = ::big;//全局 big
   return this->Age;
}