C++中 shared_ptr的拷贝和赋值——引用计数理解

　　当进行拷贝或赋值操作时，每个shared_ptr都会纪录有多少个其他shared_ptr指向相同的对象：

　　auto p = make_shared<int>(50);//p指向的对象只有p一个引用者
　　auto q = p; //p和q指向相同对象，此对象有两个引用者；

　　智能指针类能记录有多少个shared_ptr指向相同的对象，并能在恰当的时候自动释放对象！

 

　　关于shared_ptr的引用计数测试demo：

#include <iostream> #include <memory> #include <vector>
using namespace std; int main() { vector<shared_ptr<int>> intPtr; vector<shared_ptr<int>> intPtr2; for (int i = 0; i < 10; ++i) { intPtr.emplace_back(make_shared<int>(i)); } for (int i = 0; i < 10; ++i) { cout << "intPtr " << i << " = " << *intPtr.at(i) << endl; } intPtr2 = intPtr; /* cout << "2: intPtr[0].use_count() = " << intPtr[0].use_count() << endl; cout << "2: intPtr2[0].use_count() = " << intPtr2[0].use_count() << endl; */ cout << "intPtr[0] = " << intPtr[0] << endl; cout << "intPtr2[0] = " << intPtr2[0] << endl; intPtr[0] = make_shared<int>(50); cout << "3: intPtr[0].use_count() = " << intPtr[0].use_count() << endl; cout << "3: intPtr2[0].use_count() = " << intPtr2[0].use_count() << endl; cout << "intPtr[0] = " << intPtr[0] << endl; cout << "intPtr2[0] = " << intPtr2[0] << endl; cout << "intPtr[0] = " << *intPtr[0] << endl; cout << "intPtr2[0] = " << *intPtr2[0] << endl; return 0; }