通用工具

Pair和TUple

Pair

TUple

Smart Pointer

Class shared_ptr

托管 Pointer 的 最后一个shared_ptr 象在reference被删除是时,会自动执行delete释放指针。

#include <iostream>
#include <memory>

using namespace std;
class A
{
public:
    int i;
    A(int n):i(n) { };
    ~A() { cout << i << " " << "destructed" << endl; }
};
int main()
{
    shared_ptr<A> sp1(new A(2)); /* A(2)由sp1托管， */
    shared_ptr<A> sp2(sp1);      /* A(2)同时交由sp2托管 */
    shared_ptr<A> sp3;


    sp3 = sp2;                   /* A(2)同时交由sp3托管 */
    cout << "use_count : " << sp3.use_count() << endl;
    cout << sp1->i << "," << sp2->i <<"," << sp3->i << endl;

    A * p = sp3.get();          /* get返回托管的指针，p 指向 A(2) */
    cout << p->i << endl;       /* 输出 2 */

    sp1.reset(new A(3));        /* reset导致托管新的指针, 此时sp1托管A(3) */
    cout << "sp1.reset(A(3)), sp3.use_count : " << sp3.use_count() << endl;

    sp2.reset(new A(4));       /* sp2托管A(4) */
    cout << sp1->i << endl;    /* 输出 3 */
    cout << "sp2.reset(A(4)), sp3.use_count : " << sp3.use_count() << endl;

    sp3.reset(new A(5));      /* sp3托管A(5),A(2)无人托管，被delete*/
    cout << "sp3.reset(A(5)), sp3.use_count : " << sp3.use_count() << endl;


    sp3.reset();              /* 复位,A(5)无人托管，被delete*/
    cout << "sp3.reset(); sp3.use_count : " << sp3.use_count() << endl;

    cout << "end" << endl;
    return 0;
}

use_count : 3
2,2,2
2
sp1.reset(A(3)), sp3.use_count : 2
3
sp2.reset(A(4)), sp3.use_count : 1
2 destructed
sp3.reset(A(5)), sp3.use_count : 1
5 destructed
sp3.reset(); sp3.use_count : 0
end
4 destructed
3 destructed

Class unique_ptr