cpp：类中的静态成员变量和静态成员函数（class）

cpp：类中的静态成员变量和静态成员函数（class）

 

 

 

 

一、类中的静态成员变量和静态成员函数：

 

 

　　1、类中的静态成员变量和静态成员函数：它们属于‘类’不属于‘对象’， 它们没有指针‘ this ’。

 

 

　　2、类中的静态成员变量和静态成员函数：静态成员变量，只能在类外初始化；静态成员函数只能访问静态成员变量、静态成员函数以及与本类无关的函数；

 

 

　　3、伪代码：

 

#include<iostream>


using namespace std;


class information
{
public:
        information(){ count++;}
        information(int e){ count++; elem=e;}
        ~information(){ cout << "OS: ~information()" << endl; }
        void set(int e){elem=e;}
        int get(){ return elem;}
        void print_count()
        {
                // using static member count 
                cout << "print_count = " << count << endl;
        }
        static void msg();
        static void count_object();
private:
        int elem;
        static int count; 
};


// define static function msg(); no keyword 'static'
void information::msg()
{
        cout <<"\nvoid information::msg()\n" << endl;
}


// define static function count_object(), no keyword 'static'
void information::count_object()
{
        // first: using static count 
        // cout << "\ninformation_object = " << information::count << "\n" << endl;

        // second: using static count 
        cout << "\ninformation_object = " << count << "\n" << endl;
}

 

 

 

 

二、应用示例

 

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


using namespace std;


class information
{
public:
        information(){ count++;}
        information(int e){ count++; elem=e;}
        ~information(){ cout << "OS: ~information()" << endl; }
        void set(int e){elem=e;}
        int get(){ return elem;}
        void print_count()
        {
                // using static member count 
                cout << "print_count = " << count << endl;
        }
        static void msg();
        static void count_object();
private:
        int elem;
        static int count; 
};


// define static function msg(); no keyword 'static'
void information::msg()
{
        cout <<"\nvoid information::msg()\n" << endl;
}


// define static function count_object(), no keyword 'static'
void information::count_object()
{
        // first: using static count 
        // cout << "\ninformation_object = " << information::count << "\n" << endl;

        // second: using static count 
        cout << "\ninformation_object = " << count << "\n" << endl;
}


// static variable initial; no keyword 'static'
int information::count = 0;


// using static member function
void use_static_member_function()
{
        // using static member function
        information::count_object();
}


// create information object , oject number is 'size'. 
information* create_information_object(int size)
{
        information* pointer_information;
        information object_array[size];
        pointer_information = object_array;

        return pointer_information;
}


// use the function 'print_count()' of an object array of information.
void use_information_object(information* pointer_information, int size)
{
        cout <<"\n"<< endl;
        for(int i=0; i<size; i++)
        {
                pointer_information -> print_count();
                pointer_information++;
        }
        cout <<"\n"<< endl;

}


// test part.
int main(int argc, char* argv[], char* envp[])
{

        // print count, when it initializes.
        // information::count_object();
        use_static_member_function();

        // information create 10 objects.
        information* ptinfo ;
        ptinfo = create_information_object(10);
        use_information_object(ptinfo, 10);

        // print count, after information creates 10 ojects.
        // information::count_object();
        use_static_member_function();

        return 0;
}
[root@rockylinux tmp]# 
[root@rockylinux tmp]# 
[root@rockylinux tmp]# ./static_member_function_class 

information_object = 0

OS: ~information()
OS: ~information()
OS: ~information()
OS: ~information()
OS: ~information()
OS: ~information()
OS: ~information()
OS: ~information()
OS: ~information()
OS: ~information()


print_count = 10
print_count = 10
print_count = 10
print_count = 10
print_count = 10
print_count = 10
print_count = 10
print_count = 10
print_count = 10
print_count = 10



information_object = 10

[root@rockylinux tmp]# 
[root@rockylinux tmp]#