一 查看内存：
adb shell 进入,命令： dumpsys meminfo 包名
MyTeacher teacher；
- C++中 这个语句执行完毕，在当前的堆内存内 初始化并且赋值好该对象
- 在java中执行这个语句，只是开辟了一块内存空间，并没初始化和赋值对象，
必须用new关键字，来进行初始化和赋值
二 引用
Teacher.h
class MyTeacher
{
public:
~MyTeacher();//析构函数 释放在构造函数里面动态申请的内存 (free)
MyTeacher(int age,char *name);
void setAge(int age);
int getAge();
void setName(char *name);
char* getName();
private:
int age;
char *name;
};
Teacher.cpp
#include <Teacher.h>
#include <iostream>
//c++ 标准库的命名空间
using namespace std;
MyTeacher::MyTeacher(int age,char *name):name(name),age(age) {
cout << " MyTeacher 构造函数 地址：" << this << endl;
}
MyTeacher::~MyTeacher() {
cout << " MyTeacher 析构函数 地址：" << this << endl;
}
// ::代表限定符
void MyTeacher::setAge(int age) {
this->age = age;
}
int MyTeacher::getAge() {
return this->age;
}
void MyTeacher::setName(char *name) {
this->name = name;
}
char* MyTeacher::getName() {
return this->name;
}
调用：
#include <Teacher.h>
#include <iostream>
using namespace std;
void fun() {
MyTeacher teacher = MyTeacher(18, "zhangsan");
cout << "teacher name:" << teacher.getName() << endl;
cout << "teacher age:" << teacher.getAge() << endl;
}
void main() {
fun();
system("pause");
}
结果：
MyTeacher 构造函数 地址：00D7F884
teacher name:zhangsan
teacher age:18
MyTeacher 析构函数 地址：00D7F884
三 指针
void fun() {
MyTeacher *teacher = new MyTeacher(18, "zangsan");
cout << "teacher name:" << teacher->getName() << endl;
cout << "teacher age:" << teacher->getAge() << endl;
// delete teacher;
// teacher = nullptr;
}
结果：
MyTeacher 构造函数 地址：0113E950
teacher name:zangsan
teacher age:18
没有调用析构函数，需要delete teacher;才会调用
四 拷贝构造函数
使用场景
- 值传递
- 赋值语句
MyStudent.h
class MyStudent
{
public:
MyStudent(int age,char *name,char *teacherName);
~MyStudent();
//重写默认的拷贝构造函数
MyStudent(const MyStudent &student);
public:
int age;
char *name;
char *teacherName;
};
MyStudent.cpp
#include <MyStudent.h>
#include <iostream>
using namespace std;
MyStudent::MyStudent()
{
cout << " MyStudent 构造函数 地址：" << this << endl;
}
MyStudent::~MyStudent()
{
cout << " MyStudent 析构函数 地址：" << this << endl;
}
//默认构造函数 浅拷贝
MyStudent::MyStudent(const MyStudent &student) {
cout << " MyStudent 拷贝构造函数 地址：" << this << endl;
this->age = student.age;
this->name = student.name;
this->teacherName = student.teacherName;
}
调用：
void setFunX(MyStudent student) {
cout << "setFunc student name:" << student.name << endl;
cout << "setFunc student age:" << student.age << endl;
cout << "setFunc student teacherName:" << student.teacherName << endl;
}
void main() {
MyStudent student = MyStudent(21, "jack", "Jone");
setFunX(student);
system("pause");
}
结果：
MyStudent 构造函数 地址：008FFE74
MyStudent 拷贝构造函数 地址：008FFD88
setFunc student name:jack
setFunc student age:21
setFunc student teacherName:Jone
MyStudent 析构函数 地址：008FFD88
五 浅拷贝与深拷贝
- 默认的拷贝构造函数是浅拷贝
浅拷贝：
void copyTest(){
MyStudent student = MyStudent(21, "jack", "Jone");
MyStudent st2 = student;
}
浅拷贝出现的问题
修改构造、析构函数
MyStudent::MyStudent(int age, char *name, char *teacherName):age(age)
{
cout << " MyStudent 构造函数 地址：" << this << endl;
int len = strlen(name);
this->name = (char *)malloc(len + 1);
strcpy(this->name, name);
len = strlen(teacherName);
this->teacherName = (char *)malloc(len + 1);
strcpy(this->teacherName, teacherName);
}
MyStudent::~MyStudent()
{
cout << " MyStudent 析构函数 地址：" << this << endl;
free(this->name);
free(this->teacherName);
}
错误：
C4996 'strcpy': This function or variable may be unsafe. Consider using strcpy_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS. See online help for details. Project2 c:\users\pf0zybaj\source\repos\project2\project2\src\mystudent.cpp 11
解决：属性 ->C/C+±>命令行 ：-D _CRT_SECURE_NO_WARNINGS ->应用
继续运行，打印正常，任意键退出时对报错，free已经释放了，拷贝构造函数执行了，拷贝对象释放野指针释放出错
为了避免浅拷贝出现的问题有两个解决方法：
1 深拷贝
MyStudent::MyStudent(const MyStudent &student) {
cout<<"MyStudent 深拷贝构造函数 地址：" << this << endl;
int len = strlen(student.name);
this->name = (char *)malloc(len + 1);
strcpy(this->name, student.name);
len = strlen(student.teacherName);
this->teacherName = (char *)malloc(len + 1);
strcpy(this->teacherName, student.teacherName);
}
2 私有化拷贝构造函数（不常用）
六 Demo
