【例子驱动学习】unique_ptr

写这个是为了熟悉unique_ptr的接口，注意它与auto_ptr的区别。本测试包含三部分。
1. 测试指向POD类型的unique_ptr
2. 测试unique_ptr的各种成员函数 测试用例来自cplusplus.com
3. 测试函数参数，返回值为unique_ptr的注意事项。

代码

/** ---------------------------------------------------*  Copyright (c) 2017 josan All rights reserved.* ---------------------------------------------------**               创建者： Josan*             创建时间： 2017/9/20 8:37:47*/#define _CRTDBG_MAP_ALLOC#include <cstdlib>#include <crtdbg.h>#include <memory>   //unique_ptr#include <iostream>using namespace std;//---------------测试指向POD类型的unique_ptr()  test_POD()-------------------void deleteInt(int* p){    cout << "Ready to delete an int" << endl;    delete p;}void test_POD(){    //1 ctor, copy ctor(=delete  不存在拷贝赋值)unique_ptr (const unique_ptr&) = delete;   但可以有移动拷贝复制    //空unique_ptr    unique_ptr<int> u1;    unique_ptr<int> u2(new int{2});    ////error  这个使用模板参数2的构造函数，也就是空指针，这个存在问题，因此错误  因此只有u5是可以运行的    //unique_ptr<int, decltype(deleteInt)*> u3;    //unique_ptr<int, decltype(deleteInt)*> u4(new int);           unique_ptr<int, decltype(deleteInt)*> u5(new int(3), deleteInt);    //unique_ptr<int, decltype(deleteInt)*> u6(deleteInt);   //error    unique_ptr<int, decltype(deleteInt)*> u7(new int(111), deleteInt);    //u7.reset(u5.release());    //2 assign  (unique_ptr& operator= (const unique_ptr&) = delete;)    //释放u指向的对象，同时将u置为空    u1 = nullptr;    ////error  无法直接赋值    //u1 = u2;    u1 = move(u2);    //3 测试 release 和 reset 成员函数    //WARNINGS: u2释放指针，并返回指针的值。如果没有捉住这个指针，就会产生内存泄漏    u2.release();  //泄漏    u2.reset(new int{100});    //u2释放指针    u2.reset();    //u2本身指向为空，仍可以继续reset()    u2.reset(nullptr);    int * p = new int{123};    u2.reset(p);    //常见reset的用法    u1.reset(u2.release());}//---------------测试unique_ptr的各种成员函数  测试用例来自cplusplus.com-------static void testCtor(){    std::default_delete<int> d;    std::unique_ptr<int> u1;    std::unique_ptr<int> u2(nullptr);    std::unique_ptr<int> u3(new int);    std::unique_ptr<int> u4(new int, d);    std::unique_ptr<int> u5(new int, std::default_delete<int>());    //ERROR: 测试不通过，但是cplusplus的意思是测试通过啊。    //std::unique_ptr<int> u6(std::move(u5));    //std::unique_ptr<void> u7(std::move(u6));    std::unique_ptr<int> u8(std::auto_ptr<int>(new int));    std::cout << "u1: " << (u1 ? "not null" : "null") << '\n';  //null    std::cout << "u2: " << (u2 ? "not null" : "null") << '\n';  //null    std::cout << "u3: " << (u3 ? "not null" : "null") << '\n';  //not null    std::cout << "u4: " << (u4 ? "not null" : "null") << '\n';  //not null    std::cout << "u5: " << (u5 ? "not null" : "null") << '\n';  //null    //std::cout << "u6: " << (u6 ? "not null" : "null") << '\n';  //null    //std::cout << "u7: " << (u7 ? "not null" : "null") << '\n';  //not null    std::cout << "u8: " << (u8 ? "not null" : "null") << '\n';  //not null}static void testCtorWithMyDeleter(){    auto deleter = [](int*p) {        std::cout << "[deleter called]\n";        delete p;    };    std::unique_ptr<int, decltype(deleter)> foo(new int, deleter);    std::cout << "foo " << (foo ? "is not" : "is") << " empty\n";}static void testAssignment(){    std::unique_ptr<int> foo;    std::unique_ptr<int> bar;    foo = std::unique_ptr<int>(new int(101));  // rvalue    bar = std::move(foo);                       // using std::move    std::cout << "foo: ";    if(foo) std::cout << *foo << '\n'; else std::cout << "empty\n";    std::cout << "bar: ";    if(bar) std::cout << *bar << '\n'; else std::cout << "empty\n";}//测试成员函数get()static void testGet(){    //01 -------------test get()-------------------------    void testGet();    // foo   bar    p    // ---   ---   ---    std::unique_ptr<int> foo;                // null    std::unique_ptr<int> bar;                // null  null    int* p = nullptr;                        // null  null  null    foo = std::unique_ptr<int>(new int(10)); // (10)  null  null    bar = std::move(foo);                    // null  (10)  null    //NOTE:此时bar依然保存有指针    p = bar.get();                           // null  (10)  (10)    *p = 20;                                 // null  (20)  (20)    p = nullptr;                             // null  (20)  null    foo = std::unique_ptr<int>(new int(30)); // (30)  (20)  null    p = foo.release();                       // null  (20)  (30)    *p = 40;                                 // null  (20)  (40)    std::cout << "foo: ";    if(foo) std::cout << *foo << '\n'; else std::cout << "(null)\n";    std::cout << "bar: ";    if(bar) std::cout << *bar << '\n'; else std::cout << "(null)\n";    std::cout << "p: ";    if(p) std::cout << *p << '\n'; else std::cout << "(null)\n";    std::cout << '\n';    delete p;   // the program is now responsible of deleting the object pointed by p                // bar deletes its managed object automatically}class state_deleter{  // a deleter class with state    int count_;public:    state_deleter() : count_(0)    {    }    template <class T>    void operator()(T* p)    {        std::cout << "[deleted #" << ++count_ << "]\n";        delete p;    }};//测试成员函数get_deleter()static void testGet_deleter(){    state_deleter del;    std::unique_ptr<int> p;   // uses default deleter                              // alpha and beta use independent copies of the deleter:    std::unique_ptr<int, state_deleter> alpha(new int);    std::unique_ptr<int, state_deleter> beta(new int, alpha.get_deleter());    // gamma and delta share the deleter "del" (deleter type is a reference!):    std::unique_ptr<int, state_deleter&> gamma(new int, del);    std::unique_ptr<int, state_deleter&> delta(new int, gamma.get_deleter());  //二者共享同一个删除器    std::cout << "resetting alpha..."; alpha.reset(new int);    std::cout << "resetting beta..."; beta.reset(new int);    std::cout << "resetting gamma..."; gamma.reset(new int);    std::cout << "resetting delta..."; delta.reset(new int);    std::cout << "calling gamma/delta deleter...";    gamma.get_deleter()(new int);    alpha.get_deleter() = state_deleter();  // a brand new deleter for alpha                                            // additional deletions when unique_ptr objects reach out of scope                                            // (in inverse order of declaration)    //结束之前，alpha, beta, gamma, delta中的count 分别为0， 1， 3， 3    //Result:------------------------    //resetting alpha...[deleted #1]    //  resetting beta...[deleted #1]    //  resetting gamma...[deleter #1]    //  resetting delta...[deleter #2]    //  calling gamma / delta deleter...[deleted #3]    //  [deleted #4]    //[deleted #5]          //[deleted #2]    //[deleter #1]}//测试成员函数swap()static void testSwap(){    std::unique_ptr<int> foo(new int(10));    std::unique_ptr<int> bar(new int(20));    foo.swap(bar);    std::cout << "foo: " << *foo << '\n';    std::cout << "bar: " << *bar << '\n';}static void testMemberFunction(){    ////测试成员函数get()   注意此时源地址未失效    //testGet();    ////测试成员函数get_deleter()    //testGet_deleter();    ////测试转换函数，也就是转换成bool    ////略. Oops...    ////测试reset(), release()    ////略. Oops...    ////测试swap    //testSwap();}//从cplusplus摘取的测试用例。static void testFromCPlusPlus(){    //测试构造函数    testCtor();    //测试带自定义删除器    testCtorWithMyDeleter();    //测试赋值函数    testAssignment();    //测试成员函数    testMemberFunction();}unique_ptr<int> fun(unique_ptr<int> u){    cout << "fun: u -> " << *u << endl;    return u;}//return u会报错，无法引用已经删除的u??unique_ptr<int> fun1(unique_ptr<int>& u){    cout << "fun: u -> " << *u << endl;    return move(u);    //return u; 报错}//返回一个引用，也就是意味着返回的是一个lvalue;unique_ptr<int>& fun2(unique_ptr<int> u){    cout << "fun: u -> " << *u << endl;    return u;}unique_ptr<int>& fun3(unique_ptr<int>& u){    cout << "fun: u -> " << *u << endl;    return u;}static void testParameterPass(){    unique_ptr<int> u1(new int{100});    ////这个会出现无法转换    //unique_ptr<int> u2 = fun(u1);    unique_ptr<int> u3 = fun(move(u1));   //返回的临时变量是rvalue; 另外，u1指向为空    //or:  unique_ptr<int> u3 = move(fun(move(u1)));    cout << *u3 << endl;    //other test:   For fun.    关于引用相关的测试    //unique_ptr<int> u4 = fun1(u3);          //u3为空    //cout << *u4 << endl;                      //100    //unique_ptr<int> u5 = move(fun2(move(u3)));    ////unique_ptr<int> u5 = fun2(move(u3));    //这个会报错，引用已经删除的变量    //cout << *u5 << endl;                    //一个随机数   1904870    这种传值是错误的    //unique_ptr<int> u6 = move(fun3(u3));    //cout << *u6 << endl;       //100    {        unique_ptr<int>& u6 = u3;        cout << *u6 << endl;   //100    *u3---100    }    cout << *u3 << endl;    //仍然可以正确输出100}//总测试static void test(){    ////测试指向POD类型的unique_ptr()    //test_POD();    ////测试unique_ptr的各种成员函数  测试用例来自cplusplus.com    //testFromCPlusPlus();    //测试参数传递    testParameterPass();    //测试多态，包括指针的upcast，和downcast的转换。    //wait to test}int main(){    _CrtSetDbgFlag(_CRTDBG_ALLOC_MEM_DF | _CRTDBG_LEAK_CHECK_DF);    test();    return 0;}

总结

• unique_ptr没有直接的拷贝构造函数以及拷贝赋值语句，也就是说unique_ptr<T> u(u1);是错的，正确的写法是unique_ptr<T> u(move(u1));。
• 对于函数的返回值。如果不是引用，返回值默认是rvalue；如果是引用，返回值默认是lvalue。
• 对于函数参数传递的一个假设。貌似无论直接传参数，还是传引用，都能将实参给销毁掉。