C++ 构造函数-CFANZ编程社区

费曼学习法

https://wiki.mbalib.com/wiki/%E8%B4%B9%E6%9B%BC%E5%AD%A6%E4%B9%A0%E6%B3%95

1、把它教给一个小孩子
2、回顾，找到自己知识的边缘
3、把语言条理化，简化
4、再传授

命名空间

using namespacing std;
std:cout<<"输出函数"<<endl;

//自定义命名空间
namespace ZoranLee{
  int age =33;
  char *name = "ZoranLee";
  void show() {
        cout << "name:" << name << "age:" << age << endl;
    }
}

int main() {
// using namespace ZoranLee;
//    show();//直接调用 配合 using namespace ZoranLee;
//    cout << ZoranLee::age << ZoranLee::name << endl;//使用命名空间调用
}

两个命名空间重复的函数

//新增命名空间 ZoranLee1
namespace ZoranLee1 {
    void show() {
        cout << "hello world" << endl;
    }
}

using namespace ZoranLee1;

int main(){
//直接调用show 是会报错,需要使用::调用
  ZoranLee1::show();
  ZoranLee::show();
return 0 ;
};

命名空间的嵌套

namespace ZoranLee{
  namespace ZoranLee1{
    namespace ZoranLee2{
    int age= 30;
  char * name = "name";
}
}
}

using namespace std;
using namespace ZoranLee::ZoranLee1::ZoranLee2;
int main(){
//直接嵌套引出
cout<<ZoranLee::ZoranLee1::ZoranLee2::age<<endl;//1
cout<<age<<endl;//2
}

构造函数

#include "iostream"
using namespace std;
class Student {
public:
    Student() {
        cout << "无参构造" << endl;
    }

    Student(char *name) : name(name) {
        cout << "一个参数的构造" << endl;
//        this->name = name;
    }

    Student(char *name,int age) {
        cout << "两个参数的构造" << endl;
        this->age = age;
        this->name = name;
    }

    void setAge(int age) {
        this->age = age;
    }

    void setName(char *name) {
        this->name = name;
    }

    int getAge() {
        return this->age;
    }

    char *getName() {
        return this->name;
    }
private:
    int age;
    char *name;
};

//使用栈区构造函数
int main() {
//    Student *stu = new Student();

    Student stu;//无参构造
    stu.setAge(30);
    stu.setName("名字");
    cout << stu.getAge() << "\n" << stu.getName() << endl;

    Student stu1("名字",30); //调用两个参数构造
    cout << stu1.getAge() << "\n" << stu1.getName() << endl;
    return 0;
}

构造函数之间相互调用


 Student(char *name) :Student(name,30) {
        cout << "一个参数的构造" << endl;
        this->name = name;
    }

//会先调用两个参数的构造，再调用一个参数的构造
int main(){
Student stu("名字");
return 0 ;
}

堆区使用

  Student * stu = new Student("名字",30);
  cout<<stu.getName<<endl;
  delete stu;//回收 不能使用free

Student * stu =(Student *) malloc(sizeof Student);
free(stu);

析构函数

析构函数(destructor) 与构造函数相反，当对象结束其生命周期，如对象所在的函数已调用完毕时，系统自动执行析构函数。析构函数往往用来做“清理善后” 的工作（例如在建立对象时用new开辟了一片内存空间，delete会自动调用析构函数后释放内存）。
delete会调用
不能传参

this ->name = (char *)malloc(sizeof(char*)*10);
strcpy(this->name,name);

~Student(){
  if(this->name){
    free(this->name);
    this->name = NULL;
  }
}

//两个参数的构造函数
Student(char * name,int age):name(name),age(age){
}

new/delete;malloc/free

拷贝构造函数

引子

  struct Person{
int age;
char * name;
}
int main(){
  Person person = {20, "张三丰"};
    Person person2 = person;
    std::cout <<"person:"<< &person2 << "；" << &person << std::endl;
    std::cout << "name:" << &(person2.name) << "；" << &(person.name) << std::endl;
    std::cout << "age:"<< &(person2.age) << "；" << &(person.age) << std::endl;

//    person:0x7ffee83342a0；0x7ffee83342b0
//    name:0x7ffee83342a8；0x7ffee83342b8
//    age:0x7ffee83342a0；0x7ffee83342b0
     return 0;
}

由以上打印结果可以看出，在栈空间是将person的值赋值给person2对应的成员，他们地址都不相同，只是值赋值

拷贝函数
对象1 = 对象2 会执行默认的拷贝构造函数

class Student {
public:
    Student() {

    }

    Student(int age, char *name) {
        this->age = age;
        this->name = name;
    }

    Student(const Student &student) {
        cout << "拷贝构造函数" << endl;
        this->name = student.name;
        this->age = student.age - 10;
    }

    char *getName() {
        return this->name;
    }

    int getAge() {
        return this->age;
    }

private:
    int age;
    char *name;
};

int main() {
    Student stu(30, "张三");
    Student stu2 = stu;
//    Student stu2 ;    
//     stu2 = stu;//这种方式就不调用拷贝函数
    cout << stu2.getAge() << stu2.getName() << endl;
}

使用堆空间

  
    Student *stu = new Student(30, "zhang");
    Student *stu2 = stu;
    stu2->setName("ssss");
    cout << stu->getName() << stu->getAge() << endl;
    cout << stu2->getName() << stu2->getAge() << endl;
    cout << "stu地址：" << &stu << endl;
    cout << "stu2地址：" << &stu2 << endl;

stu name地址：0x7fcee6c02b78
ssss;30
stu name地址：0x7fcee6c02b78
ssss;30
stu地址：0x7ffeebca42b8
stu2地址：0x7ffeebca42a0