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tr1::unique_ptr 和 SelectObject()

发布于 2024-09-17 09:44:24 字数 7493 浏览 4 评论 0原文

我有一些管理异常安全的原始代码，如下所示：

void foo() {
    HDC hdc = //get an HDC
    HBITMAP hbitmap = //get an HBITMAP

    HGDIOBJ hbitmapOld = SelectObject(hdc, hbitmap);

    try {
        //do something that may throw an exception
    } catch (...) {
        SelectObject(hdc, hbitmapOld);
        throw;
    }
}

现在我想摆脱 try 块并使用 unique_ptr 自动选择旧位图。所以我写了这样的东西：

void foo() {
    //...

    //HGDIOBJ is defined as void*
    std::unique_ptr<void, std::function<HGDIOBJ(HGDIOBJ)>>
        hbitmapOld(SelectObject(hdc, hbitmap), std::bind(SelectObject, hdc, _1));
}

但它不能编译。怎样做才对呢？

错误信息：

1>c:\program files (x86)\microsoft visual studio 10.0\vc\include\xxcallfun(7): error C2664: 'HGDIOBJ (HDC,HGDIOBJ)' : cannot convert parameter 2 from 'boost::arg<I>' to 'HGDIOBJ'
1>          with
1>          [
1>              I=1
1>          ]
1>          No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\xxbind1(292) : see reference to function template instantiation '_Ret std::tr1::_Callable_fun<_Ty,_Indirect>::_ApplyX<_Ret,_Arg&,boost::arg<I>&>(_Arg0,_Arg1) const' being compiled
1>          with
1>          [
1>              _Ret=_Rx,
1>              _Ty=HGDIOBJ (__stdcall *const )(HDC,HGDIOBJ),
1>              _Indirect=false,
1>              _Arg=HDC,
1>              I=1,
1>              _Arg0=HDC &,
1>              _Arg1=boost::arg<1> &
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\xxbind0(31) : see reference to function template instantiation '_Ret std::tr1::_Bind2<_Callable,_Arg0,_Arg1>::_ApplyX<_Rx,void&,std::tr1::_Nil&,std::tr1::_Nil&,std::tr1::_Nil&,std::tr1::_Nil&,std::tr1::_Nil&,std::tr1::_Nil&,std::tr1::_Nil&,std::tr1::_Nil&,std::tr1::_Nil&>(_Barg0,_Barg1,_Barg2,_Barg3,_Barg4,_Barg5,_Barg6,_Barg7,_Barg8,_Barg9)' being compiled
1>          with
1>          [
1>              _Ret=_Rx,
1>              _Callable=std::tr1::_Callable_fun<HGDIOBJ (__stdcall *const )(HDC,HGDIOBJ),false>,
1>              _Arg0=HDC,
1>              _Arg1=boost::arg<1>,
1>              _Barg0=HGDIOBJ &,
1>              _Barg1=std::tr1::_Nil &,
1>              _Barg2=std::tr1::_Nil &,
1>              _Barg3=std::tr1::_Nil &,
1>              _Barg4=std::tr1::_Nil &,
1>              _Barg5=std::tr1::_Nil &,
1>              _Barg6=std::tr1::_Nil &,
1>              _Barg7=std::tr1::_Nil &,
1>              _Barg8=std::tr1::_Nil &,
1>              _Barg9=std::tr1::_Nil &
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\xxcallobj(13) : see reference to function template instantiation 'void *std::tr1::_Bind_base<_Ret,_BindN>::operator ()<_Arg0&>(_Carg0)' being compiled
1>          with
1>          [
1>              _Ret=HGDIOBJ ,
1>              _BindN=std::tr1::_Bind2<std::tr1::_Callable_fun<HGDIOBJ (__stdcall *const )(HDC,HGDIOBJ),false>,HDC,boost::arg<1>>,
1>              _Arg0=HGDIOBJ,
1>              _Carg0=HGDIOBJ &
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\xxfunction(65) : see reference to function template instantiation '_Ret std::tr1::_Callable_obj<_Ty>::_ApplyX<_Rx,_Arg0&>(void)' being compiled
1>          with
1>          [
1>              _Ret=HGDIOBJ,
1>              _Ty=std::tr1::_Bind<HGDIOBJ,HGDIOBJ,std::tr1::_Bind2<std::tr1::_Callable_fun<HGDIOBJ (__stdcall *const )(HDC,HGDIOBJ),false>,HDC,boost::arg<1>>>,
1>              _Rx=HGDIOBJ,
1>              _Arg0=HGDIOBJ
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\xxfunction(64) : while compiling class template member function 'HGDIOBJ std::tr1::_Impl_no_alloc1<_Callable,_Rx,_Arg0>::_Do_call(_Arg0)'
1>          with
1>          [
1>              _Callable=_MyWrapper,
1>              _Rx=HGDIOBJ ,
1>              _Arg0=HGDIOBJ 
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\xxfunction(386) : see reference to class template instantiation 'std::tr1::_Impl_no_alloc1<_Callable,_Rx,_Arg0>' being compiled
1>          with
1>          [
1>              _Callable=_MyWrapper,
1>              _Rx=HGDIOBJ ,
1>              _Arg0=HGDIOBJ 
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\xxfunction(369) : see reference to function template instantiation 'void std::tr1::_Function_impl1<_Ret,_Arg0>::_Reset0o<_Myimpl,_Fty,std::allocator<_Ty>>(_Fty,_Alloc)' being compiled
1>          with
1>          [
1>              _Ret=HGDIOBJ ,
1>              _Arg0=HGDIOBJ ,
1>              _Fty=std::tr1::_Bind<HGDIOBJ,HGDIOBJ,std::tr1::_Bind2<std::tr1::_Callable_fun<HGDIOBJ (__stdcall *const )(HDC,HGDIOBJ),false>,HDC,boost::arg<1>>>,
1>              _Ty=std::tr1::_Function_impl1<HGDIOBJ ,HGDIOBJ >,
1>              _Alloc=std::allocator<std::tr1::_Function_impl1<HGDIOBJ ,HGDIOBJ >>
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\functional(113) : see reference to function template instantiation 'void std::tr1::_Function_impl1<_Ret,_Arg0>::_Reset<_Fx>(_Fty)' being compiled
1>          with
1>          [
1>              _Ret=HGDIOBJ ,
1>              _Arg0=HGDIOBJ ,
1>              _Fx=std::tr1::_Bind<HGDIOBJ,HGDIOBJ,std::tr1::_Bind2<std::tr1::_Callable_fun<HGDIOBJ (__stdcall *const )(HDC,HGDIOBJ),false>,HDC,boost::arg<1>>>,
1>              _Fty=std::tr1::_Bind<HGDIOBJ,HGDIOBJ,std::tr1::_Bind2<std::tr1::_Callable_fun<HGDIOBJ (__stdcall *const )(HDC,HGDIOBJ),false>,HDC,boost::arg<1>>>
1>          ]
1>          r:\programming\windows\biota\library\orchid\src\pixmap.cpp(182) : see reference to function template instantiation 'std::tr1::function<_Fty>::function<std::tr1::_Bind<_Result_type,_Ret,_BindN>>(_Fx)' being compiled
1>          with
1>          [
1>              _Fty=HGDIOBJ (HGDIOBJ),
1>              _Result_type=HGDIOBJ,
1>              _Ret=HGDIOBJ,
1>              _BindN=std::tr1::_Bind2<std::tr1::_Callable_fun<HGDIOBJ (__stdcall *const )(HDC,HGDIOBJ),false>,HDC,boost::arg<1>>,
1>              _Fx=std::tr1::_Bind<HGDIOBJ,HGDIOBJ,std::tr1::_Bind2<std::tr1::_Callable_fun<HGDIOBJ (__stdcall *const )(HDC,HGDIOBJ),false>,HDC,boost::arg<1>>>
1>          ]
1>c:\program files (x86)\microsoft visual studio 10.0\vc\include\xxcallfun(7): error C2664: 'HGDIOBJ (HDC,HGDIOBJ)' : cannot convert parameter 1 from 'boost::arg<I>' to 'HDC'
1>          with
1>          [
1>              I=1
1>          ]
1>          No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called
1>
1>Build FAILED.
原文

I have some original code that manages exception safety like this:

void foo() {
    HDC hdc = //get an HDC
    HBITMAP hbitmap = //get an HBITMAP

    HGDIOBJ hbitmapOld = SelectObject(hdc, hbitmap);

    try {
        //do something that may throw an exception
    } catch (...) {
        SelectObject(hdc, hbitmapOld);
        throw;
    }
}

Now I want to get rid of the try block and use unique_ptr to select the old bitmap automatically. So I wrote something like this:

void foo() {
    //...

    //HGDIOBJ is defined as void*
    std::unique_ptr<void, std::function<HGDIOBJ(HGDIOBJ)>>
        hbitmapOld(SelectObject(hdc, hbitmap), std::bind(SelectObject, hdc, _1));
}

But it doesn't compile. How to make it right?

Error message:

1>c:\program files (x86)\microsoft visual studio 10.0\vc\include\xxcallfun(7): error C2664: 'HGDIOBJ (HDC,HGDIOBJ)' : cannot convert parameter 2 from 'boost::arg<I>' to 'HGDIOBJ'
1>          with
1>          [
1>              I=1
1>          ]
1>          No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\xxbind1(292) : see reference to function template instantiation '_Ret std::tr1::_Callable_fun<_Ty,_Indirect>::_ApplyX<_Ret,_Arg&,boost::arg<I>&>(_Arg0,_Arg1) const' being compiled
1>          with
1>          [
1>              _Ret=_Rx,
1>              _Ty=HGDIOBJ (__stdcall *const )(HDC,HGDIOBJ),
1>              _Indirect=false,
1>              _Arg=HDC,
1>              I=1,
1>              _Arg0=HDC &,
1>              _Arg1=boost::arg<1> &
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\xxbind0(31) : see reference to function template instantiation '_Ret std::tr1::_Bind2<_Callable,_Arg0,_Arg1>::_ApplyX<_Rx,void&,std::tr1::_Nil&,std::tr1::_Nil&,std::tr1::_Nil&,std::tr1::_Nil&,std::tr1::_Nil&,std::tr1::_Nil&,std::tr1::_Nil&,std::tr1::_Nil&,std::tr1::_Nil&>(_Barg0,_Barg1,_Barg2,_Barg3,_Barg4,_Barg5,_Barg6,_Barg7,_Barg8,_Barg9)' being compiled
1>          with
1>          [
1>              _Ret=_Rx,
1>              _Callable=std::tr1::_Callable_fun<HGDIOBJ (__stdcall *const )(HDC,HGDIOBJ),false>,
1>              _Arg0=HDC,
1>              _Arg1=boost::arg<1>,
1>              _Barg0=HGDIOBJ &,
1>              _Barg1=std::tr1::_Nil &,
1>              _Barg2=std::tr1::_Nil &,
1>              _Barg3=std::tr1::_Nil &,
1>              _Barg4=std::tr1::_Nil &,
1>              _Barg5=std::tr1::_Nil &,
1>              _Barg6=std::tr1::_Nil &,
1>              _Barg7=std::tr1::_Nil &,
1>              _Barg8=std::tr1::_Nil &,
1>              _Barg9=std::tr1::_Nil &
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\xxcallobj(13) : see reference to function template instantiation 'void *std::tr1::_Bind_base<_Ret,_BindN>::operator ()<_Arg0&>(_Carg0)' being compiled
1>          with
1>          [
1>              _Ret=HGDIOBJ ,
1>              _BindN=std::tr1::_Bind2<std::tr1::_Callable_fun<HGDIOBJ (__stdcall *const )(HDC,HGDIOBJ),false>,HDC,boost::arg<1>>,
1>              _Arg0=HGDIOBJ,
1>              _Carg0=HGDIOBJ &
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\xxfunction(65) : see reference to function template instantiation '_Ret std::tr1::_Callable_obj<_Ty>::_ApplyX<_Rx,_Arg0&>(void)' being compiled
1>          with
1>          [
1>              _Ret=HGDIOBJ,
1>              _Ty=std::tr1::_Bind<HGDIOBJ,HGDIOBJ,std::tr1::_Bind2<std::tr1::_Callable_fun<HGDIOBJ (__stdcall *const )(HDC,HGDIOBJ),false>,HDC,boost::arg<1>>>,
1>              _Rx=HGDIOBJ,
1>              _Arg0=HGDIOBJ
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\xxfunction(64) : while compiling class template member function 'HGDIOBJ std::tr1::_Impl_no_alloc1<_Callable,_Rx,_Arg0>::_Do_call(_Arg0)'
1>          with
1>          [
1>              _Callable=_MyWrapper,
1>              _Rx=HGDIOBJ ,
1>              _Arg0=HGDIOBJ 
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\xxfunction(386) : see reference to class template instantiation 'std::tr1::_Impl_no_alloc1<_Callable,_Rx,_Arg0>' being compiled
1>          with
1>          [
1>              _Callable=_MyWrapper,
1>              _Rx=HGDIOBJ ,
1>              _Arg0=HGDIOBJ 
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\xxfunction(369) : see reference to function template instantiation 'void std::tr1::_Function_impl1<_Ret,_Arg0>::_Reset0o<_Myimpl,_Fty,std::allocator<_Ty>>(_Fty,_Alloc)' being compiled
1>          with
1>          [
1>              _Ret=HGDIOBJ ,
1>              _Arg0=HGDIOBJ ,
1>              _Fty=std::tr1::_Bind<HGDIOBJ,HGDIOBJ,std::tr1::_Bind2<std::tr1::_Callable_fun<HGDIOBJ (__stdcall *const )(HDC,HGDIOBJ),false>,HDC,boost::arg<1>>>,
1>              _Ty=std::tr1::_Function_impl1<HGDIOBJ ,HGDIOBJ >,
1>              _Alloc=std::allocator<std::tr1::_Function_impl1<HGDIOBJ ,HGDIOBJ >>
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\functional(113) : see reference to function template instantiation 'void std::tr1::_Function_impl1<_Ret,_Arg0>::_Reset<_Fx>(_Fty)' being compiled
1>          with
1>          [
1>              _Ret=HGDIOBJ ,
1>              _Arg0=HGDIOBJ ,
1>              _Fx=std::tr1::_Bind<HGDIOBJ,HGDIOBJ,std::tr1::_Bind2<std::tr1::_Callable_fun<HGDIOBJ (__stdcall *const )(HDC,HGDIOBJ),false>,HDC,boost::arg<1>>>,
1>              _Fty=std::tr1::_Bind<HGDIOBJ,HGDIOBJ,std::tr1::_Bind2<std::tr1::_Callable_fun<HGDIOBJ (__stdcall *const )(HDC,HGDIOBJ),false>,HDC,boost::arg<1>>>
1>          ]
1>          r:\programming\windows\biota\library\orchid\src\pixmap.cpp(182) : see reference to function template instantiation 'std::tr1::function<_Fty>::function<std::tr1::_Bind<_Result_type,_Ret,_BindN>>(_Fx)' being compiled
1>          with
1>          [
1>              _Fty=HGDIOBJ (HGDIOBJ),
1>              _Result_type=HGDIOBJ,
1>              _Ret=HGDIOBJ,
1>              _BindN=std::tr1::_Bind2<std::tr1::_Callable_fun<HGDIOBJ (__stdcall *const )(HDC,HGDIOBJ),false>,HDC,boost::arg<1>>,
1>              _Fx=std::tr1::_Bind<HGDIOBJ,HGDIOBJ,std::tr1::_Bind2<std::tr1::_Callable_fun<HGDIOBJ (__stdcall *const )(HDC,HGDIOBJ),false>,HDC,boost::arg<1>>>
1>          ]
1>c:\program files (x86)\microsoft visual studio 10.0\vc\include\xxcallfun(7): error C2664: 'HGDIOBJ (HDC,HGDIOBJ)' : cannot convert parameter 1 from 'boost::arg<I>' to 'HDC'
1>          with
1>          [
1>              I=1
1>          ]
1>          No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called
1>
1>Build FAILED.

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评论（3）

倥絔 2024-09-24 09:44:33

感谢 AshleysBrain 和 Nemanja Trifunovic 提出了范围防护方法的建议。

我的看法是 unique_ptr 是作用域保护的更通用的实现（它应该能够执行作用域保护所做的事情，甚至更多），并且我的方法的逻辑是正确的，所以理论上它应该有效。

经过一些测试，我终于明白为什么它不起作用了。这是因为 SelectObject() 使用 __stdcall 约定，而微软在编写 std::bind 时选择忽略自身的这种不方便的行为。 :(

Thank you, AshleysBrain and Nemanja Trifunovic, for suggesting a scope guard approach.

The way I see it is that unique_ptr is a more general implementation of scope guard (it should be able to do what scope guard does, and something more), and the logic of my method is correct, so in theory it should work.

After some testing I finally get why it doesn't work. It's because SelectObject() uses the __stdcall convention, and Microsoft chooses to ignore this inconvenient behavior of itself when writing std::bind. :(

回复 原文
人心善变 2024-09-24 09:44:31

您想要的是 Scope Guard 习惯用法： http://www.drdobbs.com/cpp/184403758< /a>

What you want here is the Scope Guard idiom: http://www.drdobbs.com/cpp/184403758

回复 原文
尤怨 2024-09-24 09:44:30

我认为更好的解决方案是编写一个小类，它将在构造函数中完成工作，并在析构函数中进行回滚。当堆栈在异常期间展开时，始终会调用堆栈类的析构函数。我认为即使你的 unique_ptr 代码正常工作，它也是一个比这更尴尬的解决方案。

例如，在我的一些代码中，我有一个 scoped_noredraw 类，它可以防止窗口在更新时刷新。如果函数正常返回或异常返回，则窗口刷新始终在析构函数中重新打开。

I think a better solution is to write a small class that will do the work in the constructor, and do the roll-back in the destructor. Destructors are always called for stack classes when the stack unwinds during exceptions. I think even if you got your unique_ptr code working, it's a much more awkward solution than that.

For example, in some of my code, I have a scoped_noredraw class that prevents a window refreshing while it is updated. If the function returns either normally or by exception, the window refreshing is always turned back on in the destructor.

回复 原文
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