c++ - unique_ptr 用于数组特化的 lambda 自定义删除器

Question

这个问题在这里已经有了答案:

How do I use a custom deleter with a std::unique_ptr member? (10 个回答)

关闭 4年前.

我最近开始将大量现有 C++ 应用程序代码移植到 C++11，现在我正在转换为新的智能指针 std::unique_ptr 和 std::shared_ptr，我有一个关于自定义删除器的具体问题。我想添加一个 lambda 记录器来查看我的删除被调用的位置，但我无法获得要编译的数组特化版本。非常感谢您的建议。

我一直在寻找用于 VC++10 或 GCC 4.5.2+unique_ptr 的数组特化自定义删除器的示例，但未果。强>。我想在 lambda 中调用删除器时打印一条日志消息 - 主要是为了确保我认为超出范围的所有指针都在这样做。这对于特化的数组版本是否可行？我可以让它与非数组版本一起工作，如果我将外部结构“MyArrayDeleter”作为第二个参数传递，我也可以让它与数组特化一起工作。还有一件事，是否可以删除丑陋的 std::function，因为我认为我可以让 lambda 签名解决这个问题。

struct MySimpleDeleter {
    void operator()(int* ptr) const {
        printf("Deleting int pointer!\n");
        delete ptr;
    }
};
struct MyArrayDeleter {
    void operator()(int* ptr) const {
        printf("Deleting Array[]!\n");
        delete [] ptr;
    }
};
{
    // example 1 - calls MySimpleDeleter where delete simple pointer is called
    std::unique_ptr<int, MySimpleDeleter> ptr1(new int(5));

    // example 2 - correctly calls MyArrayDeleter where delete[] is called
    std::unique_ptr<int[], MyArrayDeleter> ptr2(new int[5]);

    // example 3 - this works (but default_delete<int[]> would have been passed
    // even if I did not specialize it as it is the default second arg
    // I only show it here to highlight the problem I am trying to solve
    std::unique_ptr<int[], std::default_delete<int[]>> ptr2(new int[100]);

    // example 3 - this lambda is called correctly - I want to do this for arrays
    std::unique_ptr<int, std::function<void (int *)>> ptr3(
        new int(3), [&](int *ptr){ 
            delete ptr; std::cout << "delete int* called" << std::endl; 
        });

    // example 4 - I cannot get the following like to compile
    // PLEASE HELP HERE - I cannot get this to compile
    std::unique_ptr<int[], std::function<void (int *)>> ptr4(
        new int[4], [&](int *ptr){  
            delete []ptr; std::cout << "delete [] called" << std::endl; 
        });
}

The compiler error is as follows:

The error from the compiler (which complains about the new int[4] for ptr4 below is:
'std::unique_ptr<_Ty,_Dx>::unique_ptr' : cannot access private member declared in class 'std::unique_ptr<_Ty,_Dx>'
1>          with
1>          [
1>              _Ty=int [],
1>              _Dx=std::tr1::function<void (int *)>
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\memory(2513) : see declaration of 'std::unique_ptr<_Ty,_Dx>::unique_ptr'
1>          with
1>          [
1>              _Ty=int [],
1>              _Dx=std::tr1::function<void (int *)>
1>          ]

Answer 1

怎么样:

auto deleter=[&](int* ptr){...};
std::unique_ptr<int[], decltype(deleter)> ptr4(new int[4], deleter);