[cpp]: class/struct -- 初始化‘实例对象’

[cpp]: class/struct -- 初始化‘实例对象’

 

 

 

 

一、说明

 

　　1、编译标准：　　std = c++20

 

　　2、编译语句：　　g++ -std=c++20 -O2 -Wall -pedantic -pthread main.cpp && ./a.out

 

 

 

 

二、class/struct（初始化‘实例对象’）

 

　　1、class/struct 定义和初始化：

// class/struct defined
class/struct object
{
public:
    object(){}
    object(string s ): name(s){}
    object(string s, string t) :name{s}, type{t}{}
private:
    string name;
    string type;
};


// class/struct initialization
string s="sun-wukong";
string t="monkey";


// o1() -> object()
object o1();


// o2() -> object(string s)
object o2(s);


// o3() -> object(string s)
object o3{t};


// o4() -> object(string s, string t)
object o3{s, t};

 

 

二、源程序

#include <iostream>
#include <string>
#include <vector>


using namespace std;


class user_wt{
public:

    // init object: user_wt o1(); user_wt o2{}
    user_wt(){}

    // init object: user_wt o3(s,t); user_wt o4{s,t};
    user_wt(string s, string t):name(s), type(t){}

    // init object: user_wt o5{x,y,z};
    user_wt(string x, string y, string z):name{x}, type{y}{}

    void out(){ cout << "\nname := " << name << endl; cout << "type := " << type << endl; }
    void out_order(int i){ cout << "\nname_"<< i << " := " << name << endl; cout << "type_"<< i << " := " << type << endl; }
    
private:
    string name = "USER_NULL";
    string type = "USER_NULL";
};

template<class T>
void
init(string *x, string *y, T *t)
{
    for(int i=0; i<4; i++)
    {
        t[i] = user_wt(x[i], y[i]);    
    }
}

template<class U>
void
output(U *u)
{
    for(int j=0; j<4; j++)
    {
        u[j].out_order(j);  
    }
}


void run()
{

    string s[] = {"sun-wukong", "zhu-wuneng", "sha-wujing", "tang-xuanzang" };
    string t[] = {"monkey", "pig", "unknown", "human" };
    user_wt o[4];
    
    init<user_wt>(s, t, o);
    output<user_wt>(o);
    
    
    string u = "sun-wukong";
    string v = "monkey";
    string w = "whatis";
    
    user_wt w1;
    w1.out();
    
    user_wt w2(u,v);
    w2.out();
    
    // 'w3{}' calls 'user_wt::user_wt()' to initialization;  w3{} CALL user_wt::user_wt();
    user_wt w3{};
    w3.out();
    
    // 'w4{u, v, w}' call 'user_wt::user_wt(string x, string y, string z)' for initialization.
    user_wt w4{u,v,w};
    w4.out();

}


int main()
{
    run();
    
    return 0;
}

 

 

三、运行结果

name_0 := sun-wukong
type_0 := monkey

name_1 := zhu-wuneng
type_1 := pig

name_2 := sha-wujing
type_2 := unknown

name_3 := tang-xuanzang
type_3 := human

name := USER_NULL
type := USER_NULL

name := sun-wukong
type := monkey

name := USER_NULL
type := USER_NULL

name := sun-wukong
type := monkey

 

 

四、参考资料

 

　　1、　Constructors and member initializer lists　　----　　https://en.cppreference.com/w/cpp/language/constructor

 

　　2、　　cpp online tools　　----　　https://coliru.stacked-crooked.com/