shared_ptr< T []>的问题；包装动态数组 [英] Problems with shared_ptr<T[]> wrapping a dynamic array
问题描述
我想用 std :: shared_ptr 替换班级中的一些原始指针，以便在创建该类的副本时不必担心。但是原始指针指向动态数组。当您给它提供自定义删除器（例如，things）时，可以将shared_ptr与动态数组一起使用。 default_delete< T []> 。
I wanted to replace some raw pointers in my class with a std::shared_ptr so that I don't have to worry when I create copies of that class. But the raw pointers point to a dynamic array. Using a shared_ptr with dynamic arrays is possible when you give it a custom deleter, e. g. default_delete<T[]>.
但是一旦我尝试分配，我就会得到一个很大的错误列表
But I get a big error list as soon as I try to assign a new value to that field, even on construction.
这是一个最小的代码示例：
Here's a minimal code sample:
#include <memory>
#include <cstddef>
using namespace std;
template<typename T> shared_ptr<T[]> make_shared_array(size_t size)
{
return shared_ptr<T[]>(new T[size], default_delete<T[]>());
}
struct Foo
{
shared_ptr<char[]> field;
};
int main()
{
Foo a;
// This line produces the error.
a.field = make_shared_array<char>(256);
return 0;
}
NB： 是的，我知道我可以/应该 vector 而不是动态数组。但是他们的表现是不一样的。我做了一些繁重的图像处理，并且数组容纳了像素。在低于VGA分辨率的情况下，处理时间从8秒增加到11秒。
NB: Yes, I know that I could/should vector instead of dynamic arrays. But their performance is not the same. I do some heavy image processing and the arrays hold the pixels. On less than VGA resolution the processing time increased from 8 to 11 s. That's quite a lot.
更新：当然，我可以在这里提供错误信息。我只是不知道是否应该将问题描述弄得一团糟。但是这里是：
Update: Of course I can provide the errors here. I just didn't know if I should clutter the problem description with it. But here it is:
C：\Program Files（x86）\Microsoft Visual Studio 11.0\VC\INCLUDE\内存（754）：错误C2664：'std :: _ Ptr_base< _Ty> :: _ Reset0'：无法将参数1从'char '转换为'char（）[]'
with
[
_Ty = char []
]
指向的类型无关。转换需要reinterpret_cast，C样式强制转换或函数样式强制转换
C：\程序文件（x86）\ Microsoft Visual Studio 11.0\VCCINCLUDE\memory（723）：请参见参考函数模板实例化'void std :: shared_ptr< _Ty> :: __ Resetp0< _Ux>（_ Ux *，std :: _ Ref_count_base *）'正在编译
与
[
_Ty = char []，
_Ux = char
]
C：\Program Files（x86）\Microsoft Visual Studio 11.0\VC\INCLUDE\memory（723）：请参见对正在编译的函数模板实例化'void std :: shared_ptr< _Ty> :: _ Resetp0< _Ux>（_ Ux *，std :: _ Ref_count_base *）'的引用
与
[
_Ty = char []，
_Ux = char
]
C：\Program Files（x86）\Microsoft Visual Studio 11.0\VC\INCLUDE\memory（494）：请参见对函数模板实例化的引用'void std :: shared_pt r< _Ty> :: _ Resetp< _Ux，_Dx>（_ Ux *，_ Dx）'正在编译
与
[
_Ty = char []，
_Ux =字符，
_Dx = std :: default_delete
]
C：\程序文件（x86）\ Microsoft Visual Studio 11.0\VC\INCLUDE\memory（494）：请参见对正在编译的函数模板实例化'void std :: shared_ptr< _Ty> :: _ Resetp< _Ux，_Dx>（_ Ux *，_ Dx）'的引用< br>
与
[
_Ty = char []，
_Ux = char，
_Dx = std： ：default_delete
]
problem.cpp（9）：请参见对函数模板实例化'std :: shared_ptr< _Ty> :: shared_ptr>（_ Ux *，_ Dx）'的引用编译后的
与
[
_Ty = char []，
T = char，
_Ux =字符，
_Dx = std :: default_delete
]
problem.cpp（9）：请参见正在编译的函数模板实例化'std :: shared_ptr< _Ty> :: shared_ptr>（_ Ux *，_ Dx）'的引用
[
_Ty = char []，
T = char，
_Ux = char，
_Dx = std :: default_delete
]
problem.cpp（21）：请参见正在编译的函数模板实例化'std :: shared_ptr< _Ty> make_shared_array（size_t）'的引用< br>
与
[
_Ty = char []
]
C:\Program Files (x86)\Microsoft Visual Studio 11.0\VC\INCLUDE\memory(754) : error C2664: 'std::_Ptr_base<_Ty>::_Reset0' : cannot convert parameter 1 from 'char ' to 'char ()[]'
with
[
_Ty=char []
]
Types pointed to are unrelated; conversion requires reinterpret_cast, C-style cast or function-style cast
C:\Program Files (x86)\Microsoft Visual Studio 11.0\VC\INCLUDE\memory(723) : see reference to function template instantiation 'void std::shared_ptr<_Ty>::_Resetp0<_Ux>(_Ux *,std::_Ref_count_base *)' being compiled
with
[
_Ty=char [],
_Ux=char
]
C:\Program Files (x86)\Microsoft Visual Studio 11.0\VC\INCLUDE\memory(723) : see reference to function template instantiation 'void std::shared_ptr<_Ty>::_Resetp0<_Ux>(_Ux *,std::_Ref_count_base *)' being compiled
with
[
_Ty=char [],
_Ux=char
]
C:\Program Files (x86)\Microsoft Visual Studio 11.0\VC\INCLUDE\memory(494) : see reference to function template instantiation 'void std::shared_ptr<_Ty>::_Resetp<_Ux,_Dx>(_Ux *,_Dx)' being compiled
with
[
_Ty=char [],
_Ux=char,
_Dx=std::default_delete
]
C:\Program Files (x86)\Microsoft Visual Studio 11.0\VC\INCLUDE\memory(494) : see reference to function template instantiation 'void std::shared_ptr<_Ty>::_Resetp<_Ux,_Dx>(_Ux *,_Dx)' being compiled
with
[
_Ty=char [],
_Ux=char,
_Dx=std::default_delete
]
problem.cpp(9) : see reference to function template instantiation 'std::shared_ptr<_Ty>::shared_ptr>(_Ux *,_Dx)' being compiled
with
[
_Ty=char [],
T=char,
_Ux=char,
_Dx=std::default_delete
]
problem.cpp(9) : see reference to function template instantiation 'std::shared_ptr<_Ty>::shared_ptr>(_Ux *,_Dx)' being compiled
with
[
_Ty=char [],
T=char,
_Ux=char,
_Dx=std::default_delete
]
problem.cpp(21) : see reference to function template instantiation 'std::shared_ptr<_Ty> make_shared_array(size_t)' being compiled
with
[
_Ty=char []
]
推荐答案
您建议的解决方案是可能的，但您将失去数组的大小：
The solution you suggest is possible, but you will lose the size of the array:
#include <memory>
#include <cstddef>
using namespace std;
template<typename T> shared_ptr<T> make_shared_array(size_t size)
{
return shared_ptr<T>(new T[size], default_delete<T[]>());
}
struct Foo
{
shared_ptr<char> field;
};
int main()
{
Foo a;
a.field = make_shared_array<char>(256);
return 0;
}
我在这里所做的就是让数组衰减为指针。只要删除程序是数组删除程序，它就应该正确运行。
What I have done here is to let the array decay into a pointer. As long as the deleter is an array deleter it should behave correctly.
为防止大小丢失，并且如果不能按照建议使用boost :: shared_array，我会建议将此信息封装在您自己的shared_array类中。
To prevent this loss of size, and if you cannot use boost::shared_array as suggested, I would suggest to encapsulate this information in your own shared_array class.
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