程式設計與演算法（三）C++面向物件程式設計第二週相關筆記

阿新 • • 發佈：2021-10-07

1、

成員函式可寫在類的外面

#include<bits/stdc++.h>
using namespace std;
class student{
    public: 
        int grade;
        string name;
        void init_(string _name,int _grade){
            name = _name;
            grade = _grade;
        }
        void get_name(){
            cout<<name<<endl;
        }
         
void get_grade(){
            cout<<grade<<endl;
        }
        void together();
};
void student::together(){
    cout<<name<<" "<<grade<<endl;
}
int main(){
    student stu;
    stu.init_("Bruce",99);
    stu.get_grade();
    stu.together();
    
    
    
     
return 0;
}

2、

類的成員

有pubilc,private,protected 沒有次序，預設private

3、

成員函式同樣可以過載

4、建構函式

（1）必須public 與類同名類生成就進行

View Code

（2）過載

#include<bits/stdc++.h>
using namespace std;
class test{
    public:
        test(int x){
            cout<<"first called"<<endl;
        }
        test(){
            cout 
<<"second called"<<endl;
        }
};
int main(){
    test t1;
    cout<<endl;
    test t2[2] = {1,2};
    cout<<endl;
    test t3[2] = {1};
    cout<<endl;
    test * t4= new test[3];
    delete []t4;
    return 0;
}

View Code

#include<bits/stdc++.h>
using namespace std;
class test{
    public:
        test(int x,int y){
            cout<<"first called"<<endl;
        }
        test(int x){
            cout<<"second called"<<endl;
        }
        test(){
            cout<<"third called"<<endl;
        }
};
int main(){
    test t1;
    cout<<endl;
    test t2[2] = {1,test(1,2)};  // !
    cout<<endl;
    test t3[2] = {1};
    cout<<endl;
    test * t4= new test[3];
    cout<<endl;
    test * t5[3] = {
        new test(),new test(1),new test(1,2)
    };
    delete []t4;
    return 0;
}

View Code

5、

複製建構函式的三種使用方法

（1）初始化時

#include<bits/stdc++.h>
using namespace std;
class student{
    public: 
        int grade;
        string name;
        student (){
            ;
        }
        student (student &a);
        void get_name(){
            cout<<name<<endl;
        }
        void get_grade(){
            cout<<grade<<endl;
        }
        void together();
};
void student::together(){
    cout<<name<<" "<<grade<<endl;
}
student::student(student &a){  // 建構函式 
    name =    a.name;
    grade = a.grade;
    cout<<"Copy constructor run!"<<endl;
}
int main(){
    student stu1;
    stu1.name = "Bruce";
    stu1.grade = 99;
    student stu2(stu1);
    return 0;
}

View Code

（2）作為形參時

#include<bits/stdc++.h>
using namespace std;
class student{
    public: 
        int grade;
        string name;
        student (){
            ;
        }
        student (student &a);
        void get_name(){
            cout<<name<<endl;
        }
        void get_grade(){
            cout<<grade<<endl;
        }
        void together();
};
void student::together(){
    cout<<name<<" "<<grade<<endl;
}
student::student(student &a){  // 建構函式 
    name =    a.name;
    grade = a.grade;
    cout<<"!!!"<<endl;
}
void func(student b){
    return ;
}
int main(){
    student stu1;
    stu1.name = "Bruce";
    stu1.grade = 99;
    student stu2(stu1); 
    func(stu2);
    return 0;
}

View Code

（3）作為函式返回值

pass;

賦值時不用到建構函式如 a = b

呼叫建構函式耗時間，可以用引用，怕更改原來被引用的還可以const &A

6、
型別轉換建構函式

一個引數

#include<bits/stdc++.h>
using namespace std;
class Complex{
    double real,imag;
    public:
        // 型別轉換建構函式 
        Complex(double i){
            real = i;
            imag = 0;
        }
        void output(){
            cout<<real<<" + "<<imag<<" i"<<endl;
        }
}; 
int main(){
    Complex c = 1; 
    c.output();
    return 0;
}

View Code

7、

解構函式 == 消亡函式

#include<bits/stdc++.h>
using namespace std;
class test{
    char *p;
    public:    
        test(){
            p = new char [10];
        } 
    ~test(){
        cout<<"died!"<<endl;
        delete [] p;
    }
};
int main(){
    test t[2];
    cout<<"End Main"<<endl;
    return 0;
}

End Main
died!
died!

View Code

#include<bits/stdc++.h>
using namespace std;
class test{
    char *p;
    public:    
        test(){
            p = new char [10];
        } 
    ~test(){
        cout<<"died!"<<endl;
        delete [] p;
    }
};
int main(){
    test * p = new test [2];
    cout<<"~~~"<<endl;
    delete []p;
    cout<<"~~~"<<endl;
    return 0;
}

~~~
died!
died!
~~~