C++ RAII 教程
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原文地址: http://stackoverflow.com/questions/2635882/
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RAII tutorial for C++
提问by Joe Bloggs
I'd like to learn how to use RAII in c++. I think I know what it is, but have no idea how to implement it in my programs. A quick google search did not show any nice tutorials.
我想学习如何在 C++ 中使用 RAII。我想我知道它是什么，但不知道如何在我的程序中实现它。快速谷歌搜索没有显示任何不错的教程。
Does any one have any nice links to teach me RAII?
有没有人有任何好的链接可以教我 RAII？
采纳答案by utnapistim
There's nothing to it (that is, I don't think you need a full tutorial).
没什么可做的（也就是说，我认为您不需要完整的教程）。
RAII can be shortly explained as "Every resource requiring cleanup should be given to an object's constructor."
RAII 可以简单地解释为“每个需要清理的资源都应该提供给对象的构造函数”。
In other words:
换句话说：
Pointers should be encapsulated in smart pointer classes (see std::auto_ptr, boost::shared_ptr and boost::scoped_ptr for examples).
指针应该封装在智能指针类中（参见 std::auto_ptr、boost::shared_ptr 和 boost::scoped_ptr 示例）。
Handles requiring cleanup should be encapsulated in classes that automatically free/release the handles upon destruction.
需要清理的句柄应该封装在销毁时自动释放/释放句柄的类中。
Synchronization should rely on releasing the mutex/synchronization primitive upon scope exit (see boost::mutex::scoped_lock usage for an example).
同步应该依赖于在作用域退出时释放互斥锁/同步原语（参见 boost::mutex::scoped_lock 用法示例）。
I don't think you can really have a tutorial on RAII (not anymore than you can have one on design patterns for example). RAII is more of a way of looking at resources than anything else.
我不认为您真的可以拥有关于 RAII 的教程（例如，您无法拥有关于设计模式的教程）。RAII 更像是一种查看资源的方式。
For example, at the moment I'm coding using WinAPI and I wrote the following class:
例如，目前我正在使用 WinAPI 进行编码，并编写了以下类：
template<typename H, BOOL _stdcall CloseFunction(H)>
class checked_handle
{
public:
typedef checked_handle<H,CloseFunction> MyType;
typedef typename H HandleType;
static const HandleType NoValue;
checked_handle(const HandleType value)
: _value(value)
{
}
~checked_handle()
{
Close();
}
HandleType* operator &()
{
return &_value;
}
operator HandleType()
{
return _value;
}
private:
HandleType _value;
void Close(const HandleType newValue = NoValue)
{
CloseFunction(_value);
_value = newValue;
}
};
template<typename H,BOOL _stdcall CloseFunction(H)>
const typename checked_handle<H,CloseFunction>::HandleType
checked_handle<H,CloseFunction>::NoValue =
checked_handle<H,CloseFunction>::HandleType(INVALID_HANDLE_VALUE);
typedef checked_handle<HANDLE,::CloseHandle> CheckedHandle;
typedef checked_handle<HWINSTA,::CloseWindowStation> WinStationHandle;
typedef checked_handle<HDESK,::CloseDesktop> DesktopHandle;
typedef checked_handle<HDEVNOTIFY,::UnregisterDeviceNotification> DevNotifyHandle;
typedef checked_handle<HWND,::DestroyWindow> WindowHandle;
BOOL __stdcall CloseKey(HKEY hKey);
typedef checked_handle<HKEY,CloseKey> RegHandle;
This class doesn't include assignment and copy semantics (I removed them to provide a minimal example) so returning by value, will cause the handles to be closed twice.
这个类不包括赋值和复制语义（我删除了它们以提供一个最小的例子）所以按值返回，将导致句柄被关闭两次。
Here's how it's used:
这是它的使用方法：
class declaration:
类声明：
class Something
{
public:
// ...
private:
WindowHandle _window;
};
This member is allocated but I never call ::CloseWindow(_window._handle)explicitely (it will be called when instances of Somethinggo out of scope (as Something::~Something-> WindowHandle::WindowHandle-> ::Close(_window._value)).
该成员已分配，但我从不::CloseWindow(_window._handle)明确调用（当实例Something超出范围（如Something::~Something-> WindowHandle::WindowHandle-> ::Close(_window._value)）时将调用它。
回答by Matthew T. Staebler
The reference that I personally have found most helpful on the topic of RAII is the book Exceptional C++by Herb Sutter.
我个人认为对 RAII 主题最有帮助的参考书是 Herb Sutter所著的Exceptional C++一书。
Many of the topics covered in that book are touched on in the Guru of the Week articles by Sutter. Those articles are available at http://gotw.ca/gotw/index.htm.
该书中涵盖的许多主题在 Sutter 的 Guru of the Week 文章中都有涉及。这些文章可在http://gotw.ca/gotw/index.htm 上找到。
回答by Chubsdad
Item 13 of "Effective C+"is also pretty useful
“Effective C+”的第 13 条也很有用
