1 概述
从C++11开始C++语言越来向现代化语言转变。尤其是智能指针的引入，代码中不会直接使用new/delete了。C++11智能指针有三种分别是：shared_ptr，weak_ptr 和unique_ptr 。
2 唯一指针(unique_ptr)
unique_ptr是C++11引入的，用来管理指针，取代C++98中的auto_ptr.其类图如下：
unique_ptr的特性：
- 不可复制性，体现在拷贝构造函数和拷贝赋值函数是私有的（或delete的）
- 可移动性，体现在移动构造函数和移动赋值函数。
- 可交换性，通过swap函数交换两个unique_ptr对象
- 可重置性，通过rest函数重置管理指针
- 可释放性，通过release函数释放对指针的管理
- 可管理多种指针类型，既可以管理new分配指针和数组，也可以管理malloc分配指针，不过需要定制deleter。
2 使用实例
cpp
void UniquePtrSuite::dereference_obj_member()
{
std::unique_ptr<Array> a(new Array(10));
TEST_ASSERT_EQUALS(10, a->size())
std::cout << "\na.size=" << a->size() << std::endl;
std::unique_ptr<Array> b;
if(b)
std::cout << "\nb.size=" << b->size() << std::endl;
}通过重载->操作符，统一指针可以像原始指针一样使用。
3 接口使用
3.1 construct/get
cpp
获取管理的指针
void UniquePtrSuite::get()
{
std::default_delete<int> del;
std::unique_ptr<int> a;
std::unique_ptr<int> b(nullptr);
std::unique_ptr<int> c(new int(10));
std::unique_ptr<int> d(new int(10), del);
std::unique_ptr<int> e(new int(10), std::default_delete<int>());
std::unique_ptr<int> f(std::move(d));
TEST_ASSERT_EQUALS(true, a.get() == nullptr)
TEST_ASSERT_EQUALS(true, b.get() == nullptr)
TEST_ASSERT_EQUALS(true, c.get() != nullptr)
TEST_ASSERT_EQUALS(true, d.get() == nullptr)
TEST_ASSERT_EQUALS(true, e.get() != nullptr)
TEST_ASSERT_EQUALS(true, f.get() != nullptr)
}3.2 operator bool
可以通过if条件语句判断指针是否不为空
cpp
void UniquePtrSuite::check_bool()
{
std::default_delete<int> del;
std::unique_ptr<int> a;
std::unique_ptr<int> b(nullptr);
std::unique_ptr<int> c(new int(10));
std::unique_ptr<int> d(new int(10), del);
std::unique_ptr<int> e(new int(10), std::default_delete<int>());
std::unique_ptr<int> f(std::move(d));
TEST_ASSERT_EQUALS(false, (bool)a)
TEST_ASSERT_EQUALS(false, (bool)b)
TEST_ASSERT_EQUALS(true, (bool)c)
TEST_ASSERT_EQUALS(true, (bool)c)
TEST_ASSERT_EQUALS(true, (bool)e)
TEST_ASSERT_EQUALS(true, (bool)f)
}3.3 operator *
获取指针指向对象和变量
cpp
void UniquePtrSuite::dereference_obj()
{
std::unique_ptr<int> a(new int(10));
TEST_ASSERT_EQUALS(10, *a)
std::unique_ptr<int> b;
std::cout << "\na=" << *a << std::endl;
if(b)
std::cout << "\nb=" << *a << std::endl;
}3.3 operator ->
该接口只有类是对象情况下使用
cpp
void UniquePtrSuite::dereference_obj_member()
{
std::unique_ptr<Array> a(new Array(10));
TEST_ASSERT_EQUALS(10, a->size())
std::cout << "\na.size=" << a->size() << std::endl;
std::unique_ptr<Array> b;
if(b)
std::cout << "\nb.size=" << b->size() << std::endl;
}3.4 operator =
移动赋值操作
cpp
void UniquePtrSuite::assign()
{
std::unique_ptr<int> a(new int(10));
std::unique_ptr<int> b(new int(10));
TEST_ASSERT_EQUALS(true, (bool)a)
a = nullptr;
TEST_ASSERT_EQUALS(false, (bool)a)
//a = b; error
TEST_ASSERT_EQUALS(true, (bool)b)
a = std::move(b);
TEST_ASSERT_EQUALS(true, (bool)a)
TEST_ASSERT_EQUALS(false, (bool)b)
}3.5 release
返回并释放指针管理权
cpp
void UniquePtrSuite::release()
{
std::default_delete<int> del;
std::unique_ptr<int> a;
std::unique_ptr<int> b(nullptr);
std::unique_ptr<int> c(new int(10));
std::unique_ptr<int> d(new int(10), del);
std::unique_ptr<int> e(new int(10), std::default_delete<int>());
std::unique_ptr<int> f(std::move(d));
int* a_ptr = a.release();
int* b_ptr = b.release();
int* c_ptr = c.release();
int* d_ptr = d.release();
int* e_ptr = e.release();
int* f_ptr = f.release();
TEST_ASSERT_EQUALS(false, (bool)a)
TEST_ASSERT_EQUALS(false, (bool)b)
TEST_ASSERT_EQUALS(false, (bool)c)
TEST_ASSERT_EQUALS(false, (bool)c)
TEST_ASSERT_EQUALS(false, (bool)e)
TEST_ASSERT_EQUALS(false, (bool)f)
TEST_ASSERT_EQUALS(true, a_ptr == nullptr)
TEST_ASSERT_EQUALS(true, b_ptr == nullptr)
TEST_ASSERT_EQUALS(true, c_ptr != nullptr)
TEST_ASSERT_EQUALS(true, d_ptr == nullptr)
TEST_ASSERT_EQUALS(true, e_ptr != nullptr)
TEST_ASSERT_EQUALS(true, f_ptr != nullptr)
delete a_ptr;
delete b_ptr;
delete c_ptr;
delete d_ptr;
delete e_ptr;
delete f_ptr;
}3.6 reset
重置指针，delete管理的指针，并管理新传入指针（如果有的话）
cpp
void UniquePtrSuite::reset()
{
std::unique_ptr<int> a;
TEST_ASSERT_EQUALS(false, (bool)a)
a.reset();
TEST_ASSERT_EQUALS(false, (bool)a)
a.reset(new int(10));
TEST_ASSERT_EQUALS(true, (bool)a)
a.reset();
TEST_ASSERT_EQUALS(false, (bool)a)
}3.7 swap
交换两个指针
cpp
void UniquePtrSuite::swap()
{
std::unique_ptr<int> a;
std::unique_ptr<int> b(new int(10));
std::unique_ptr<int> c(new int(50));
std::unique_ptr<int> d(new int(100));
TEST_ASSERT_EQUALS(false, (bool)a)
a.swap(b);
TEST_ASSERT_EQUALS(true, (bool)a)
TEST_ASSERT_EQUALS(false, (bool)b)
TEST_ASSERT_EQUALS(50, *c)
TEST_ASSERT_EQUALS(100, *d)
c.swap(d);
TEST_ASSERT_EQUALS(100, *c)
TEST_ASSERT_EQUALS(50, *d)
}3.8 get_deleter
获取指针deleter
cpp
class MyDeleter
{
int count_;
public:
MyDeleter() : count_(0) {}
int count() { return count_; }
template<class T>
void operator()(T* p)
{
std::cout << "\n[deleted #" << ++count_ << "]\n";
delete p;
}
};
void UniquePtrSuite::get_deleter()
{
MyDeleter del;
std::unique_ptr<int, MyDeleter> a(new int);
std::unique_ptr<int, MyDeleter> b(new int, a.get_deleter());
std::unique_ptr<int, MyDeleter&> c(new int, del);
std::unique_ptr<int, MyDeleter&> d(new int, c.get_deleter());
auto & a_deleter = a.get_deleter();
auto & b_deleter = b.get_deleter();
auto & c_deleter = c.get_deleter();
auto & d_deleter = d.get_deleter();
a.reset();
TEST_ASSERT_EQUALS(1, a_deleter.count())
b.reset();
TEST_ASSERT_EQUALS(1, b_deleter.count())
c.reset();
TEST_ASSERT_EQUALS(1, c_deleter.count())
TEST_ASSERT_EQUALS(1, del.count())
d.reset();
TEST_ASSERT_EQUALS(2, d_deleter.count())
TEST_ASSERT_EQUALS(2, del.count())
}说明：
- 如果MyDeleter&类型，多个对象可以共享一个deleter
3.9 operator []
该接口只有在类型是数组情况下使用
cpp
void UniquePtrSuite::offeset()
{
std::unique_ptr<int[]> a (new int[5]);
for(int i = 0; i < 5; i++)
a.get()[i] = i;
for(int i = 0; i < 5; i++)
TEST_ASSERT_EQUALS(i, a[i])
for(int i = 0; i < 5; i++)
a[i] = i;
for(int i = 0; i < 5; i++)
TEST_ASSERT_EQUALS(i, a[i])
}