C++第二節（2）:複合類、析構函數、new、delete

複合類、析構函數、指針複合、new、delete

1、複合類：

     1.1 複合類的成員變量，是另一個類的對象

2、析構函數：

     2.1 收回構造函數時申請的資源，垃圾回收

     2.2 調用析構函數的兩種情況：離開對象的作用域、銷燬對象刪除一個指向對象的指針

     2.3 特點：無返回值，無參，唯一，公有

     2.4 當一個類中有指針成員變量，而且指針指向的空間是手動開闢的堆空間時，必須寫析構函數

D、複合類

Work.h

#ifndef __C__No727Class__Work__
#define __C__No727Class__Work__

#include <iostream>
using namespace std;
class Work    //最先編寫的頭文件
{
private:
    int number;    //作業數量
public:
    Work(int n);   //自定義構造函數
    ~Work();       //析構函數
    void print();  //輸出信息
};
#endif /* defined(__C__No727Class__Work__) */

Work.cpp

#include "Work.h"  //成員函數的實現
Work::Work(int n)
{
    number = n;
}
Work::~Work()
{
    cout << "析構Work" << endl;
}
void Work::print()
{
    cout << "number is :" << number << endl;
}

Student.h

#include <iostream>
#include "Work.h"    //包含
class Student
{
private:
    char *name;
    int num;
    Work w;    //類類型的私有成員變量w，表示作業
public:
    Student(char *a, int b, int c);
    ~Student();
    void print();
};
#endif /* defined(__C__No727Class__Student__) */

Student.cpp

#include "Student.h"
Student::Student(char *a, int b, int c):w(c)  //:成員變量（賦給成員變量的值），初始化列表
{
    name = a;
    num = b;
}
Student::~Student()
{
    cout << "析構Student" << endl;
}
void Student::print()
{
    w.print();
    cout << "name  is  :" << name << endl;
    cout << "num   is  :" << num << endl;
}

main.cpp

#include "Student.h"
int main()
{
    Student s("名字", 123401, 10);
    s.print();
    return 0;  //首先析構Student，過程中因需要析構Work纔可以完成析構Student，所以調用析構Work的函數
}

E、指針複合

Toy.h

#ifndef __C__No727Class__Toy__
#define __C__No727Class__Toy__

#include <iostream>
using namespace std;
class Toy
{
private:
    int number;
    
public:
    Toy(int n);
    ~Toy();
    void print();
};
#endif /* defined(__C__No727Class__Toy__) */

Toy.cpp

#include "Toy.h"
Toy::Toy(int n)
{
    number = n;
}
Toy::~Toy()
{
    cout << "析構Toy" << endl;
}
void Toy::print()
{
    cout << "number is " << number << endl;
}

Baby.h

#ifndef __C__No727Class__Baby__
#define __C__No727Class__Baby__

#include <iostream>
#include "Toy.h"
using namespace std;
class Baby
{
public:
    Baby(char * n, int a, int number);
    ~Baby();
    void print();
private:
    char * name;
    int age;
    Toy *t;    //類類型的指針
};
#endif /* defined(__C__No727Class__Baby__) */

Baby.cpp

#include "Baby.h"
Baby::Baby(char * n, int a, int number)
{
    name = n;
    age = a;
    t = new Toy(number);  //手動分配內存，指針指向new出來的堆空間，堆空間裏面是一個Toy類的對象
}
Baby::~Baby()
{
    cout << "析構Baby" << endl;
    if(t)    //如果指針所指向的空間有內容
    {
        delete t;   //手動回收內存，把new出來的空間收回
        t = NULL;   //指針置空
    }
}
void Baby::print()
{
    (*t).print();  //t -> print();
    cout << " name is " << name  << endl;
    cout << " age  is " << age << endl;
}

main.cpp

#include "Baby.h"
int main()
{
    Baby a("a", 1, 10);
    a.print();
    return 0;  //首先析構Boy，並沒有直接使用Toy的對象，所以不會自動調用析構Toy的函數，需要手動回收，delete時調用析構Toy的函數
}

F、兩個成員變量

Paper.h

#ifndef __C__No727Class__Paper__
#define __C__No727Class__Paper__

#include <iostream>
using namespace std;
class Paper
{
public:
    Paper(int n, char *s);
    ~Paper();
    void show();
private:
    int number;    //兩個成員變量
    char * subject;
};
#endif /* defined(__C__No727Class__Paper__) */

Paper.cpp

#include "Paper.h"
Paper::Paper(int n, char *s)
{
    number = n;
    subject = s;
}
Paper::~Paper()
{
    cout << "析構Paper" << endl;
}
void Paper::show()
{
    cout << "數量 is : " << number << endl;
    cout << "科目 is : "<< subject << endl;
}

Teacher.h

#ifndef __C__No727Class__Teacher__
#define __C__No727Class__Teacher__

#include <iostream>
#include "Paper.h"
class Teacher
{
private:
    int num;
    char * name;
    Paper p;
public:
    Teacher(int a, char * b, int n, char * s);
    ~Teacher();
    void show();
};
#endif /* defined(__C__No727Class__Teacher__) */

Teacher.cpp

#include "Teacher.h"
Teacher::Teacher(int a, char * b, int n, char * s):p(n, s)
{
    num = a;
    name = b;
}
Teacher::~Teacher()
{
    cout << "析構Teacher" << endl;
}
void Teacher::show()
{
    p.show();
    cout << "編號 is : " << num << endl;
    cout << "姓名 is : " << name << endl;
}

main.cpp

#include "Teacher.h"
int main()
{
    Teacher t(1234, "名字", 50, "計算機");
    t.show();
    return 0;
}