c++17(11)-委托构造函数,mutable,const,const重载,static inline

#include <iostream>
#include <cstring> 
using namespace std;

class Book
{
private:
    int _id;
    char* _name;
    float _price;
    static int nowid;
public : 
    Book(int id, char* name, float price)
        : _id(id)
        , _price(price)
    {
        int nameLen = strlen(name);
        _name = new char[nameLen + 1];
        strcpy(_name, name);
    }
    Book(char* name, float price):Book(nowid,name,price){
        nowid++;
    }
    ~Book()
    {
        delete[] _name;
    }
    void print(){
        cout<<_id<<","<<_name<<","<<_price<<endl;
    }
};
int Book::nowid{0};//static在类外初始化
int main(int argc, char **argv)
{
   Book *book1=new Book("精通C++", 52.17);
   book1->print();
   Book *book2=new Book("精通Python", 62.67);
   book2->print();   
   delete book1;
   delete book2;   
}

下面代码段定义了委托构造函数，委托Book(int id, char* name, float price)完成构造。
1、只能在初始化成员列表中调用被委托构造函数
2、成员变量只能在函数体内进行初始化，或者由被委托构造函数完成

 Book(char* name, float price):Book(nowid,name,price){
        nowid++;
    }

0,精通C++,52.17
1,精通Python,62.67

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const成员函数可返回非const和const值。
被 mutable 修饰的数据成员，可以在 const 成员函数中修改
下面的print函数被const重载后，才可以被book2调用。

#include <iostream>
#include <cstring> 
using namespace std;

class Book
{
private:
    int _id;
    char* _name;
    float _price;
    static int nowid;
    const int flag{0};
    mutable int status{0};
public : 
    Book(int id, char* name, float price)
        : _id(id)
        , _price(price)
    {
        int nameLen = strlen(name);
        _name = new char[nameLen + 1];
        strcpy(_name, name);
    }
    Book(char* name, float price):Book(nowid,name,price){
        nowid++;
    }
    ~Book()
    {
        delete[] _name;
    }
    void print(){
        cout<<_id<<","<<_name<<","<<_price<<endl;
    }
    const void print() const{
        cout<<_id<<","<<_name<<","<<_price<<endl;
    }    
    const int getNextId() const{
        return nowid;
    }
    const int getFlag() const{
        return flag;
    }    
    const void setStatus(int myStatus) const{
        status=myStatus;
    }    
    const int getStatus() const{
        return status;
    }  
};
int Book::nowid{0};
int main(int argc, char **argv)
{
   Book *book1=new Book("精通C++", 52.17);
   book1->print();
   cout<<book1->getNextId()<<endl;  
   book1->setStatus(1);
   cout<<book1->getStatus()<<endl;  
   const Book *book2=new Book("精通Python", 62.67);
   book2->print();  
   cout<<book2->getNextId()<<endl; 
   cout<<book2->getFlag()<<endl; 
   book2->setStatus(1);
   cout<<book2->getStatus()<<endl;    
   delete book1;
   delete book2;   
}

0,精通C++,52.17
1
1
1,精通Python,62.67
2
0
1

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static inline可初始化static成员 ，不用在类外初始化。

#include <iostream>
#include <cstring> 
using namespace std;

class Book
{
private:
    int _id;
    char* _name;
    float _price;
    static inline int nowid{0};
    const int flag{0};
    mutable int status{0};
public : 
    Book(int id, char* name, float price)
        : _id(id)
        , _price(price)
    {
        int nameLen = strlen(name);
        _name = new char[nameLen + 1];
        strcpy(_name, name);
    }
    Book(char* name, float price):Book(nowid,name,price){
        nowid++;
    }
    ~Book()
    {
        delete[] _name;
    }
    void print(){
        cout<<_id<<","<<_name<<","<<_price<<endl;
    }
    const void print() const{
        cout<<_id<<","<<_name<<","<<_price<<endl;
    }    
    const int getNextId() const{
        return nowid;
    }
    const int getFlag() const{
        return flag;
    }    
    const void setStatus(int myStatus) const{
        status=myStatus;
    }    
    const int getStatus() const{
        return status;
    }  
};

int main(int argc, char **argv)
{
   Book *book1=new Book("精通C++", 52.17);
   book1->print();
   cout<<book1->getNextId()<<endl;  
   book1->setStatus(1);
   cout<<book1->getStatus()<<endl;  
   const Book *book2=new Book("精通Python", 62.67);
   book2->print();  
   cout<<book2->getNextId()<<endl; 
   cout<<book2->getFlag()<<endl; 
   book2->setStatus(1);
   cout<<book2->getStatus()<<endl;    
   delete book1;
   delete book2;   
}