"shared_ptr" 拆分智能指针(smart pointer)
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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:
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/*
* CppPrimer.cpp
*
* Created on: 2013.11.4
* Author: C.L.Wang
*/
/*eclipse cdt GCC 4.8.1*/
#include
#include
#include
#include
#include
using namespace std;
int main (void) {
std::shared_ptr p(new int(256));
std::shared_ptr 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;
}
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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
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