c语言中的stl模板指针,【C++】 61_智能指针类模板
智能指针
智能指针的意义
现代 C++ 开发库中最重要的类模板之一
C++ 中内存管理的主要手段
能够在很大程度上避开内存相关的问题
内存泄漏
内存多次释放
STL 中的智能指针 auto_ptr
生命周期结束时，销毁指向的内存(防止内存泄漏)
不能指向堆数组，只能指向堆对象(变量)
一片堆空间只属于一个智能指针对象(防止内存多次释放)
多个智能指针对象不能指向同一片堆空间
编程实验： auto_ptr 使用初探
#include
#include
using namespace std;
class Test
{
private:
string m_name;
public:
Test(const char* name)
{
cout << "Hello, " << name << endl;
m_name = name;
}
void print()
{
cout << "I'm " << m_name << endl;
}
~Test()
{
cout << "Goodbye, " << m_name << endl;
}
};
int main()
{
auto_ptr pt(new Test("D.T.Software"));
cout << "pt = " << pt.get() << endl;
pt->print();
cout << endl;
auto_ptr pt1(pt); // 所有权转移 ： pt ==> pt1
cout << "pt = " << pt.get() << endl;
cout << "pt = " << pt1.get() << endl;
pt1->print();
return 0;
}
输出：
Hello, D.T.Software
pt = 0x90e7008
I'm D.T.Software
pt = 0
pt = 0x90e7008
I'm D.T.Software
Goodbye, D.T.Software
STL 中的其它指针
share_ptr
带有引用计数机制，支持多个指针对象指向同一片内存空间
weak_ptr
配合 shared_ptr 而引入的一种智能指针
unique_ptr
一个指针对象指向一片内存空间，不能拷贝构造和赋值
Qt 中的智能指针
QPointer
当其指向的对象被销毁时，他会被自动置空(防止内存多次释放)
析构时不会自动销毁所指向的对象
QSharedPointer
引用计数型智能指针
可以被自由的拷贝和赋值
当引用计数为 0 时才删除指向的对象(防止内存泄漏)
编程实验： Qt中的智能指针
#include
#include
#include
#include
class Test : public QObject
{
private:
QString m_name;
public:
Test(const char* name)
{
qDebug() << "Hello, " << name;
m_name = name;
}
void print()
{
qDebug() << "I'm " << m_name;
}
~Test()
{
qDebug() << "Goodbye, " << m_name;
}
};
int main()
{
QPointer pt(new Test("D.T.Software"));
QPointer pt1(pt);
QPointer pt2(pt);
pt->print();
pt1->print();
pt2->print();
delete pt;
qDebug() << "pt = " << pt;
qDebug() << "pt1 = " << pt1;
qDebug() << "pt2 = " << pt2;
qDebug();
QSharedPointer spt(new Test("D.T.Software"));
QSharedPointer spt1(spt);
QSharedPointer spt2(spt);
spt->print();
spt1->print();
spt2->print();
return 0;
}
输出：
Hello, D.T.Software
I'm "D.T.Software"
I'm "D.T.Software"
I'm "D.T.Software"
Goodbye, "D.T.Software"
pt = QObject(0x0)
pt1 = QObject(0x0)
pt2 = QObject(0x0)
Hello, D.T.Software
I'm "D.T.Software"
I'm "D.T.Software"
I'm "D.T.Software"
Goodbye, "D.T.Software"
Qt 中的其它智能指针
QWeakPointer
QScopedPointer
QScopedArrayPointer
QSharedDataPointer
QExplicitlySharedDataPointer
编程实验： 创建智能指针类模板
SmartPointer.h
#ifndef _SMARTPOINTER_H_
#define _SMARTPOINTER_H_
template
< typename T >
class SmartPoniter
{
private:
T* m_pointer;
public:
SmartPoniter(T* p = NULL);
SmartPoniter(const SmartPoniter& obj);
SmartPoniter& operator = (const SmartPoniter& obj);
T* operator -> ();
T& operator * ();
bool isNull();
T* get();
~SmartPoniter();
};
template
< typename T >
SmartPoniter::SmartPoniter(T* p)
{
m_pointer = p;
}
template
< typename T >
SmartPoniter::SmartPoniter(const SmartPoniter& obj)
{
m_pointer = obj.m_pointer; // 所有权转接
const_cast&>(obj).m_pointer = NULL;
}
template
< typename T >
SmartPoniter& SmartPoniter::operator = (const SmartPoniter& obj)
{
if( this != &obj )
{
delete m_pointer; // 所有权转接
m_pointer = obj.m_pointer;
const_cast&>(obj).m_pointer = NULL;
}
return *this;
}
template
< typename T >
T* SmartPoniter::operator -> ()
{
return m_pointer;
}
template
< typename T >
T& SmartPoniter::operator * ()
{
return *m_pointer;
}
template
< typename T >
bool SmartPoniter::isNull()
{
return (m_pointer == NULL);
}
template
< typename T >
T* SmartPoniter::get()
{
return m_pointer;
}
template
< typename T >
SmartPoniter::~SmartPoniter()
{
delete m_pointer;
}
#endif
main.cpp
#include
#include
#include "SmartPointer.h"
using namespace std;
class Test
{
private:
string m_name;
public:
Test(const char* name)
{
cout << "Hello, " << name << endl;
m_name = name;
}
void print()
{
cout << "I'm " << m_name << endl;
}
~Test()
{
cout << "Goofbye, " << m_name << endl;
}
};
int main()
{
SmartPoniter pt(new Test("D.T.Software"));
cout << "pt = " << pt.get() << endl;
pt->print();
cout << endl;
SmartPoniter pt1(pt);
cout << "pt = " << pt.get() << endl;
cout << "pt = " << pt1.get() << endl;
pt1->print();
return 0;
}
输出：
Hello, D.T.Software
pt = 0x815e008
I'm D.T.Software
pt = 0
pt = 0x815e008
I'm D.T.Software
Goofbye, D.T.Software
小结
智能指针是 C++ 中自动内存管理的主要手段
智能指针在各种平台上都有不同的表现形式
智能指针能够尽可能的避开内存相关的问题
STL 和 Qt 中都提供了对智能指针的支持
以上内容参考狄泰软件学院系列课程，请大家保护原创