c++智能指针使用笔记
2024-08-31 21:09:05
1. c++智能指针中，c++的memory文件中，有auto_ptr等各种关于智能指针的东西，shared_ptr，weak_ptr在C++11中已经成为标准。
也看了ogs的智能指针，每次引用起来比较麻烦，规则也多。方便的是自动的引用计数，可选线程安全。
为方便 写了个公用类，如下：
#ifndef _test_share_ptr_h__
#define _test_share_ptr_h__ #define null 0
class student
{
public:
student();
student(float score_)
:scores(score_)
{ }
virtual ~ student();
public:
char* all_class_name;
float scores;
private: }; student:: student()
{
} student::~ student()
{
if (null != all_class_name)
{
delete []all_class_name;
all_class_name = null;
}
} #endif
2.auto_ptr
功能相对简单，只能负责释加入到auto_ptr中的基类，并且基类中没有单独的到堆上申请内存。
写的两个函数测试，一个函数类：
void mem_ptr_student_new()
{
int byte_numbers = 1024;
for (int i = 0; i < count_times;i++)
{
student* pri_test_stu = new student;
mem::auto_ptr<student> pri_student_share_ptr(pri_test_stu);
pri_student_share_ptr->all_class_name = new char[byte_numbers];
for (int j = 0; j < byte_numbers;j++)
{
pri_student_share_ptr->all_class_name[j] = j;
}
pri_student_share_ptr->scores = (float)(i + 10);
}
} typedef std::vector<mem::auto_ptr<student>> mem_vector_student;
void mem_ptr_student_vector_new()
{
int byte_numbers = 1024;
mem_vector_student pri_test_vector;
/*
mem::auto_ptr_ref<mem_vector_student> pri_auto_ref(&pri_test_vector);
mem::auto_ptr<mem_vector_student> pri_vector_student_share_ptr(pri_auto_ref);
for (int i = 0; i < count_times;i++)
{
mem::auto_ptr<student> pri_student_share_ptr(new student);
pri_student_share_ptr->all_class_name = new char[byte_numbers];
for (int j = 0; j < byte_numbers;j++)
{
pri_student_share_ptr->all_class_name[j] = j;
}
pri_student_share_ptr->scores = (float)(i + 10);
pri_vector_student_share_ptr->push_back(pri_student_share_ptr);
}*/
}
结果很明显，对于这样的类，char* all_class_name 在使用中自动申请了内存，auto_ptr很明显无能为力。内存泄露明显，所以第二个函数，stl vector的使用更不用多说，
一样不行。
摘抄了一段auto_ptr使用说明：
/*---------------------------mem_auto_ptr-------------------------------------*/
/*
若下函数，使用mem::auto_ptr时候，不会自动调用student函数的析构，造成内存泄露。
摘抄部分说明： * 1）auto_ptr不能共享所有权，即不要让两个auto_ptr指向同一个对象。
* * 2）auto_ptr不能指向数组，因为auto_ptr在析构的时候只是调用delete,而数组应该要调用delete[]。
* * 3）auto_ptr只是一种简单的智能指针，如有特殊需求，需要使用其他智能指针，比如share_ptr。
* * 4）auto_ptr不能作为容器对象，STL容器中的元素经常要支持拷贝，赋值等操作，在这过程中auto_ptr会传递所有权，那么source与sink元素之间就不等价。
*/
3. 别人写的一个share_ptr,用来测试和比较说明。
此类功能复杂，代码相对多。不过，挺好用。
若有问题，随时联系，可删除。
#ifndef __smart_shared_ptr_h__
#define __smart_shared_ptr_h__ #define null 0
namespace smart
{
class shared_ptr_reference_count
{
public:
shared_ptr_reference_count()
{
_reference_count = 1;
} virtual ~shared_ptr_reference_count()
{
} void grab()
{
_reference_count++;
} size_t drop()
{
_reference_count--;
return _reference_count;
} size_t get_reference_count()
{
return _reference_count;
}
private:
size_t _reference_count;
}; class shared_ptr_reference_destory
{
public:
virtual ~shared_ptr_reference_destory(){};
}; template<class t>
class smart_shared_ptr; class smart_shared_ptr_shadow
{
public:
smart_shared_ptr_shadow()
: _reference_instance(null)
, _reference_count(null)
, _reference_destory(null)
{
} smart_shared_ptr_shadow(void *instance_, shared_ptr_reference_count* reference_count_, shared_ptr_reference_destory* reference_destory_)
: _reference_instance(instance_)
, _reference_count(reference_count_)
, _reference_destory(reference_destory_)
{
if(_reference_count != null)
{
_reference_count->grab();
}
} ~smart_shared_ptr_shadow()
{
if(_reference_count == null)
{
return;
} if(_reference_count->drop() == 0){
delete _reference_destory;
_reference_destory = null; delete _reference_count;
_reference_count = null;
}
} smart_shared_ptr_shadow(const smart_shared_ptr_shadow& right_)
{
if(right_._reference_count != null){
right_._reference_count->grab();
} _reference_instance = right_._reference_instance;
_reference_count = right_._reference_count;
_reference_destory = right_._reference_destory;
} template<class t_>
smart_shared_ptr<t_> to_shared_ptr()
{
return smart_shared_ptr<t_>((t_*)_reference_instance, _reference_count);
} template<class t_>
operator smart_shared_ptr<t_>()
{
return to_shared_ptr<t_>();
} smart_shared_ptr_shadow& operator = (const smart_shared_ptr_shadow& right_)
{
if(right_._reference_count != null)
{
right_._reference_count->grab();
} if(_reference_count != null)
{
if(_reference_count->drop() == 0)
{
delete _reference_destory;
_reference_destory = null; delete _reference_count;
_reference_count = null;
}
} _reference_instance = right_._reference_instance;
_reference_count = right_._reference_count;
_reference_destory = right_._reference_destory;
return *this;
} bool operator == (const smart_shared_ptr_shadow& right_) const
{
return (_reference_instance == right_._reference_instance);
} operator bool() const
{
return _reference_count != null;
}
private:
void* _reference_instance;
shared_ptr_reference_count* _reference_count;
shared_ptr_reference_destory* _reference_destory;
}; template<class t>
class smart_shared_ptr
{
class shared_ptr_reference_destory_impl
: public shared_ptr_reference_destory
{
public:
shared_ptr_reference_destory_impl(t* reference_instance_)
{
this->_reference_instance = reference_instance_;
} virtual ~shared_ptr_reference_destory_impl()
{
delete _reference_instance;
}
private:
t* _reference_instance;
}; public:
smart_shared_ptr()
: _reference_count(null)
, _reference_instance(null)
{ } smart_shared_ptr(t* instance_)
: _reference_count(new shared_ptr_reference_count)
, _reference_instance(instance_)
{
} smart_shared_ptr(t* instance_, shared_ptr_reference_count* reference_count_)
: _reference_count(reference_count_)
, _reference_instance(instance_)
{
if(_reference_count != null)
{
_reference_count->grab();
}
} ~smart_shared_ptr()
{
if(_reference_count == null)
{
return;
} if(_reference_count->drop() == 0)
{
delete _reference_instance;
_reference_instance = null; delete _reference_count;
_reference_count = null;
}
} t* operator -> ()
{
return _reference_instance;
} smart_shared_ptr(const smart_shared_ptr& right_)
{
if(right_._reference_count != null)
{
right_._reference_count->grab();
} _reference_instance = right_._reference_instance;
_reference_count = right_._reference_count;
} smart_shared_ptr_shadow to_shared_ptr_shadow()
{
return smart_shared_ptr_shadow(_reference_instance, _reference_count, new shared_ptr_reference_destory_impl(_reference_instance));
} template<class t_>
smart_shared_ptr<t_> to_shared_ptr()
{
return smart_shared_ptr<t_>((t_*)_reference_instance, _reference_count);
} template<class t_>
operator smart_shared_ptr<t_>()
{
return to_shared_ptr<t_>();
} operator smart_shared_ptr_shadow()
{
return to_shared_ptr_shadow();
} smart_shared_ptr& operator = (const smart_shared_ptr& right_)
{
if(right_._reference_count != null)
{
right_._reference_count->grab();
} if(_reference_count != null)
{
if(_reference_count->drop() == 0)
{
delete _reference_instance;
_reference_instance = null; delete _reference_count;
_reference_count = null;
}
} _reference_instance = right_._reference_instance;
_reference_count = right_._reference_count; return *this;
} template<class t_>
bool operator == (const smart_shared_ptr& right_) const
{
return (_reference_instance == right_.reference_instance);
} operator bool() const
{
return _reference_count != null;
} bool is_null() const
{
return _reference_count != null;
}
private:
shared_ptr_reference_count* _reference_count;
t* _reference_instance;
}; #endif
同样的测试代码，只是里面类名称改变一下。如下：
void smart_ptr_student_new()
{
int byte_numbers = 1024;
for (int i = 0; i < count_times;i++)
{
smart_shared_ptr<student> pri_student_share_ptr = new student;
pri_student_share_ptr->all_class_name = new char[byte_numbers];
for (int j = 0; j < byte_numbers;j++)
{
pri_student_share_ptr->all_class_name[j] = j;
}
pri_student_share_ptr->scores = (float)(i + 10);
}
} typedef std::vector<smart_shared_ptr<student>> vector_student;
void smart_ptr_student_vector_new()
{
int byte_numbers = 1024;
smart_shared_ptr<vector_student> pri_vector_student_share_ptr = new vector_student();
for (int i = 0; i < count_times;i++)
{
smart_shared_ptr<student> pri_student_share_ptr = new student;
pri_student_share_ptr->all_class_name = new char[byte_numbers];
for (int j = 0; j < byte_numbers;j++)
{
pri_student_share_ptr->all_class_name[j] = j;
}
pri_student_share_ptr->scores = (float)(i + 10);
pri_vector_student_share_ptr->push_back(pri_student_share_ptr);
}
}
结果：很明显，可管理类的对象指针和vector中的对象指针，因为重载了等号，括号，实时可以记录指针的使用次数，并处理了析构。计数的做为个类来处理，比有的智能
指针用个static的变量来好很多。
但是各种此类型的指针可以相互赋值，因为里面用的指针一律是void* 造成的。
3. 一个简单的ptr
不知道是否有问题啊。目前看起来还行。
#ifndef __m_smart_ptr_h__
#define __m_smart_ptr_h__ #include <iostream>
#include <stdexcept>
using namespace std; #define test_smart_ptr_cout
namespace s_smart
{
template <typename T>
class simple_smart_ptr
{
public:
simple_smart_ptr(T *p = 0): ptr(p), p_use_count(new size_t(1))
{
} simple_smart_ptr(const simple_smart_ptr& src): ptr(src.ptr), p_use_count(src.p_use_count)
{
++*p_use_count;
} simple_smart_ptr& operator= (const simple_smart_ptr& rhs) {
// self-assigning is also right
++*rhs.p_use_count;
decrUse();
ptr = rhs.ptr;
p_use_count = rhs.p_use_count;
return *this;
} T *operator->()
{
if (ptr)
return ptr;
throw std::runtime_error("access through NULL pointer");
}
const T *operator->() const
{
if (ptr)
return ptr;
throw std::runtime_error("access through NULL pointer");
} T &operator*()
{
if (ptr)
return *ptr;
throw std::runtime_error("dereference of NULL pointer");
} const T &operator*() const
{
if (ptr)
return *ptr;
throw std::runtime_error("dereference of NULL pointer");
} ~simple_smart_ptr()
{
decrUse();
#ifdef test_smart_ptr_cout
std::cout<<"simple_smart_ptr: Destructor"<<std::endl; // for testing
#endif
} private:
void decrUse()
{
if (--*p_use_count == 0) {
delete ptr;
delete p_use_count;
}
}
T *ptr;
size_t *p_use_count;
};
} #endif
同样的测试过程，均可用。对类的指针有删除能力。
以上的智能指针的操作没有线程安全。
在osg的有一个宏定义来定义，是否启用原子操作的，_OSG_REFERENCED_USE_ATOMIC_OPERATIONS，对于计数的操作是安全的。
完结了！
本文代码下载地址：http://download.csdn.net/detail/cartzhang/7004199
形式是多种的，内容是一致的。
若有问题，请及时指正！
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