C++ - "shared_ptr" 拆分智能指针(smart pointer)

"shared_ptr" 拆分智能指针(smart pointer)

两个"shared_ptr"指针, 共享内存数据, 如果其中一个修改, 则对象(object)修改, 两个指针指向的数据均修改.

如果想把两个指针拆分开, 单独修改某一个, 则需要使用, unique()和reset()方法.

如下代码所示, 只修改p, 并保持q不变, 但是两个的使用数量(use_count)均由2变化为1.

代码:

/* 
 * CppPrimer.cpp 
 * 
 *  Created on: 2013.11.4 
 *      Author: C.L.Wang 
 */  
  
/*eclipse cdt GCC 4.8.1*/  
  
#include <iostream>  
  
#include <vector>  
#include <string>  
  
#include <memory>  
#include <new>  
  
using namespace std;  
  
int main (void) {  
  
    std::shared_ptr<int> p(new int(256));  
    std::shared_ptr<int> q = p;  
    std::cout << "original : " << std::endl;  
    std::cout << "*p = " << *p << std::endl;  
    std::cout << "*q = " << *q << std::endl;  
    std::cout << "p use count : " << p.use_count() << std::endl;  
  
    *p += 256;  
    std::cout << "plus : " << std::endl;  
    std::cout << "*p = " << *p << std::endl;  
    std::cout << "*q = " << *q << std::endl;  
    std::cout << "p use count : " << p.use_count() << std::endl;  
  
    if(!p.unique())  
        p.reset(new int(*p));  
    *p += 512;  
    std::cout << "reset : " << std::endl;  
    std::cout << "*p = " << *p << std::endl;  
    std::cout << "*q = " << *q << std::endl;  
    std::cout << "p use count : " << p.use_count() << std::endl;  
  
    return 0;  
  
}

输出:

original :

*p = 256

*q = 256

p use count : 2

plus :

*p = 512

*q = 512

p use count : 2

reset :

*p = 1024

*q = 512

p use count : 1

补充：软件开发 , C++ ,