C++ new delete

01_对象和malloc

#include<iostream>
#include <stdlib.h>
#include <string.h>
using namespace std;
struct book_bag{
    int color;
    int book_sum;
    book_bag(){
        cout<<"book default constrcution!"<<endl;
    }
    book_bag(int c, int b){
        cout<<"book constrcution!"<<endl;
        color =c,book_sum = b;
    }
    ~book_bag(){
        cout<<"book destrcutor!"<<endl;
    }
};
struct Student{
    int id=1001;//成员变量或对象
    char *name=nullptr;
    int age=20;
    int score=99;
//  book_bag bg;

    Student(){cout<<"student default construction!"<<endl;}
    Student(int i,const char*n, int a,int s){
    cout<<"student "<<n<<" construction!"<<endl;
        id=i;
        if(n){
            name =(char*)malloc(strlen(n)+1);
            strcpy(name,n);
        }
        age=a;score=s;
    }
    //析构函数是释放初始化的变量
    //析构函数不可以重载
    ~Student()
    {
        cout<<"student "<<name<<" destructor!"<<endl;
        if(name)free(name);
    }

};//end class Student

int main()
{
//  Student stu1(1002,"lisi",20,90);
//  Student stu2(1003,"maliu",20,90);
//  cout<<stu1.name<<endl;

    //malloc仅仅是分配一个空间，没有任何初始化的行为
    Student *pstu1 = (Student*)malloc(sizeof(Student));
    pstu1->id =1001;
    strcpy(pstu1->name,"zhangsan");
    pstu1->age=20;
    pstu1->score=100;
    //pstu1->set_age(20);

    cout<<pstu1->id<<endl;
    //free仅仅是一个空间的回收，没有任何析构的行为
    free(pstu1);

    return 0;
}

02_对象和new

#include<iostream>
#include <stdlib.h>
#include <string.h>
using namespace std;
struct book_bag{
    int color;
    int book_sum;
    book_bag(){
        cout<<"book default constrcution!"<<endl;
    }
    book_bag(int c, int b){
        cout<<"book constrcution!"<<endl;
        color =c,book_sum = b;
    }
    ~book_bag(){
        cout<<"book destrcutor!"<<endl;
    }
};
struct Student{
    int id=1001;//成员变量或对象
    char *name=nullptr;
    int age=20;
    int score=99;
//  book_bag bg;

    Student(){cout<<"student default construction!"<<endl;}
    Student(int i,const char*n, int a,int s){
    cout<<"student "<<n<<" construction!"<<endl;
        id=i;
        if(n){
            name =(char*)malloc(strlen(n)+1);
            strcpy(name,n);
        }
        age=a;score=s;
    }
    //析构函数是释放初始化的变量
    //析构函数不可以重载
    ~Student()
    {
        cout<<"student "<<name<<" destructor!"<<endl;
        if(name)free(name);
    }

};//end class Student

int main()
{
//  Student stu1(1002,"lisi",20,90);
//  Student stu2(1003,"maliu",20,90);
//  cout<<stu1.name<<endl;

//  Student *pstu1 = (Student*)malloc(sizeof(Student));
    //new完成的事情分两步：
    //1,申请空间，此处和malloc做的一样
    //2,调用对应的构造函数，进行初始化
    //3,返回的地址不用强制类型转换
    Student *pstu2 = new Student(1001,"zhangsan",20,100);
    /*
    pstu1->id =1001;
    strcpy(pstu1->name,"zhangsan");
    pstu1->age=20;
    pstu1->score=100;
    //pstu1->set_age(20);
*/
//  cout<<pstu1->id<<endl;
    cout<<pstu2->id<<endl;
//  free(pstu1);
    //delete做的事情分两步：
    //1,先调用析构函数
    //2,然后再释放对象本身
    delete pstu2;
    pstu2 =nullptr;
    pstu2->age=21;

    return 0;
}