cpp: 指针和引用（class & object）

cpp:  指针和引用（class & object）

 

 

 

 

一、指针使用、引用的运用

 

 

　　1、指针具有双重赋值的属性：第一重赋值，为指针变量赋值内存地址；第二重赋值，为指针变量所指的内存的存储空间赋予内容。

 

　　2、（引用：cpp的特性；“引用”作为函数的参数）："引用"仍然是值传递。和普通变量相比较，“引用”只是不产生变量的临时副本。

 

[root@rockylinux tmp]# uname -a
Linux rockylinux 4.18.0-372.19.1.el8_6.x86_64 #1 SMP Tue Aug 2 16:19:42 UTC 2022 x86_64 x86_64 x86_64 GNU/Linux
[root@rockylinux tmp]# 
[root@rockylinux tmp]# 
[root@rockylinux tmp]# g++ --version
g++ (GCC) 8.5.0 20210514 (Red Hat 8.5.0-10)
Copyright (C) 2018 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

[root@rockylinux tmp]# 
[root@rockylinux tmp]# 
[root@rockylinux tmp]# cat reference.cpp 
#include<iostream>


using namespace std;


int* return_value1(int& para)
{
        int* tmp = &para;  // 可以获取para的地址；
        return tmp;
}


int* return_value2(int& para)
{
        return &para;   // 可以返回para的地址；
}


int* return_value3(int& para)
{
        return para;    // 如果这里报错，就说明“‘引用’是值传递”；
}


int main(int argc, char* argv[], char* envp[])

int main(int argc, char* argv[], char* envp[])
{

        int ref = 1949;


        int* pt1 = nullptr;
        int* pt2 = nullptr;
        int* pt3 = nullptr;


        pt1 = return_value1(ref);
        cout << "pt1 = " << *pt1 << endl;
        pt2 = return_value2(ref);
        cout << "pt2 = " << *pt2 << endl;
        pt3 = return_value3(ref);
        cout << "pt3 = " << *pt3 << endl;


        return 0;


}
[root@rockylinux tmp]# 
[root@rockylinux tmp]# 
[root@rockylinux tmp]# g++ -o reference reference.cpp 
reference.cpp: In function ‘int* return_value3(int&)’:
reference.cpp:22:9: error: invalid conversion from ‘int’ to ‘int*’ [-fpermissive]
  return para; // 如果这里报错，就说明“‘引用’是值传递”；
         ^~~~
reference.cpp: At global scope:
reference.cpp:28:1: error: expected initializer before ‘int’
 int main(int argc, char* argv[], char* envp[])
 ^~~
[root@rockylinux tmp]# 
[root@rockylinux tmp]# 

 

 

 

 

二、代码和运行结果

 

[root@rockylinux tmp]# uname -a
Linux rockylinux 4.18.0-372.19.1.el8_6.x86_64 #1 SMP Tue Aug 2 16:19:42 UTC 2022 x86_64 x86_64 x86_64 GNU/Linux
[root@rockylinux tmp]# 
[root@rockylinux tmp]# 
[root@rockylinux tmp]# g++ --version
g++ (GCC) 8.5.0 20210514 (Red Hat 8.5.0-10)
Copyright (C) 2018 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

[root@rockylinux tmp]# 
[root@rockylinux tmp]# 
[root@rockylinux tmp]# cat mix_data_structure.cpp 
#include<iostream>
#include<string>


using namespace std;


template<typename N, typename I>
struct persion{
        string uid;
        N uname;
        I uinformation;
};


class msg
{
public:
        msg()
        {
                uid = new string;
                uname = new string;
                uinformation = new string;
        }
        msg(string* id, string* name, string* info)
        { 
                uid = new string;
                uname = new string;
                uinformation = new string;

                *uid=*id; 
                *uname=*name;
                *uinformation=*info;
        }
        msg(const msg* message)
        {
                uid = new string;
                uname = new string;
                uinformation = new string;

                *uid = *message->uid;
                *uname = *message->uname;
                *uinformation = *message->uinformation;
        }
        ~msg(){ delete uid; delete uname; delete uinformation;}


        void set_uid(string* id)
        {
                *uid=*id;
        }

        string* get_uid()
        {
                return uid;
        }


        void set_uname(string* name)
        {
                *uname=*name;
        }

        string* get_uname()
        {
                return uname;
        }

        void set_uinformation(string* info)
        {
                *uinformation=*info;
        }

        string* get_uinformation()
        {
                return uinformation;
        }
private:
        string* uid;
        string* uname;
        string* uinformation;
};


template<class N, class I>
class student
{
public:
        student(){ stud.uid="usr_null"; stud.uname="usr_null"; stud.uinformation="usr_null";}
        student(string* id, N* name, I* info){ stud.uid=*id; stud.uname=*name; stud.uinformation=*info;}
        student(const student& st){ stud.uid=st.uid; stud.uname=st.uname; stud.uinformation=st.uinformation;}
        void set_all(string id, N name, I info){ stud.uid=id; stud.uname=name, stud.uinformation=info;}
        string get_uid(){ return stud.uid;}
        N get_uname(){ return stud.uname;}
        I get_uinformation(){ return stud.uinformation;}
        void print_result()
        {
                cout << "OS_STUDENT:";
                cout << "\tid=" << stud.uid;
                cout << ",\tname=" << stud.uname;
                cout << ",\tinformation=" << stud.uinformation << endl;
        }
private:
        persion<N,I> stud;
};


class teacher
{
public:
        teacher(){ message = new msg;}
        teacher(string* id, string* name, string* info)
        { 
                message= new msg; 
                message->set_uid(id);
                message->set_uname(name); 
                message->set_uinformation(info);
        }
        teacher(const teacher& t)
        { 
                message = new msg;
                message ->set_uid(t.message->get_uid()); 
                message ->set_uname(t.message->get_uname());
                message ->set_uinformation(t.message->get_uinformation());
        }
        ~teacher(){delete message;}
        void print_result()
        {
                cout <<"OS_TEACHER:";
                cout <<"\tid=" << *message->get_uid();
                cout <<",\tname="<< *message->get_uname();
                cout <<",\tinformation="<< *message->get_uinformation()<< endl;
        }
private:
        msg* message;
};



int main(int argc, char* argv[], char* envp[])
{

        string id = "20220830";
        string name = "tiger";
        string info = "forest_universe";

        string* pointer_id = &id;
        string* pointer_name = &name;
        string* pointer_info = &info;


        student<string, string> st(pointer_id, pointer_name, pointer_info);
        st.print_result();


        teacher tr(pointer_id, pointer_name, pointer_info);
        tr.print_result();


        return 0;


}
[root@rockylinux tmp]# 
[root@rockylinux tmp]# 
[root@rockylinux tmp]# g++ -o mix_data_structure mix_data_structure.cpp 
[root@rockylinux tmp]# 
[root@rockylinux tmp]# 
[root@rockylinux tmp]# ./mix_data_structure 
OS_STUDENT:     id=20220830,    name=tiger,     information=forest_universe
OS_TEACHER:     id=20220830,    name=tiger,     information=forest_universe
[root@rockylinux tmp]# 
[root@rockylinux tmp]#