如何调用非托管 C++ C# 中以 std::vector 作为参数的函数？

发布于 2024-09-24 16:20:03 字数 425 浏览 7 评论 0原文

出于性能原因，我有一个 C# 前端和一个 C++ 后端。现在我想调用一个 C++ 函数，例如：

void findNeighbors(Point p, std::vector<Point> &neighbors, double maxDist);

我想要一个 C# 包装函数，例如：

List<Point> FindNeigbors(Point p, double maxDist);

我可以将像 Point[] 这样的平面数组传递给非托管 C++ dll，但问题是，我不知道要分配多少内存，因为我不知道函数将返回的元素数量...

是否有一种优雅的方法来处理这个问题，而不会遇到内存泄漏的问题？

感谢您的帮助！

本杰明

原文

I have a C# front end and a C++ backend for performance reasons.
Now I would like to call a C++ function like for example:

void findNeighbors(Point p, std::vector<Point> &neighbors, double maxDist);

What I'd like to have is a C# wrapper function like:

List<Point> FindNeigbors(Point p, double maxDist);

I could pass a flat array like Point[] to the unmanaged C++ dll, but the problem is, that I don't know how much memory to allocate, because I don't know the number of elements the function will return...

Is there an elegant way to handle this without having troubles with memory leaks?

Thanks for your help!

Benjamin

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染火枫林 2024-10-01 16:20:03

这里最好的解决方案是用 C 语言编写一个仅限于非 C++ 类的包装函数。重要的 C++ 类本质上是通过 PInvoke 层不可编组的 [1]。相反，让包装函数使用更传统的 C 签名，该签名很容易针对

void findNeigborsWrapper(
  Point p,
  double maxDist, 
  Point** ppNeighbors,
  size_t* pNeighborsLength)

[1] 进行 PInvoke。是的，在某些情况下您可以摆脱它，但这是例外，而不是规则。

The best solution here is to write a wrapper function in C which is limited to non-C++ classes. Non-trivial C++ classes are essentially unmarshable via the PInvoke layer [1]. Instead have the wrapper function use a more traditional C signature which is easy to PInvoke against

void findNeigborsWrapper(
  Point p,
  double maxDist, 
  Point** ppNeighbors,
  size_t* pNeighborsLength)

[1] Yes there are certain cases where you can get away with it but that's the exception and not the rule.

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箜明 2024-10-01 16:20:03

阻抗不匹配严重。您必须用 C++/CLI 语言编写包装器，以便可以构造向量。另一个问题是 Point，您的 C++ 声明与它的托管版本不兼容。您的代码应该与此类似，将其从 CLR 节点添加到类库项目中。

#include <vector>

using namespace System;
using namespace System::Collections::Generic;

struct Point { int x; int y; };
void findNeighbors(Point p, std::vector<Point> &neighbors, double maxDist);

namespace Mumble {

    public ref class Wrapper
    {
    public:
        List<System::Drawing::Point>^ FindNeigbors(System::Drawing::Point p, double maxDist) {
            std::vector<Point> neighbors;
            Point point; point.x = p.X; point.y = p.Y;
            findNeighbors(point, neighbors, maxDist);
            List<System::Drawing::Point>^ retval = gcnew List<System::Drawing::Point>();
            for (std::vector<Point>::iterator it = neighbors.begin(); it != neighbors.end(); ++it) {
                retval->Add(System::Drawing::Point(it->x, it->y));
            }
            return retval;
        }
    };
}

请注意复制集合的成本，这会很快消除您可能从用本机 C++ 编写算法中获得的性能优势。

The impedance mismatch is severe. You have to write a wrapper in the C++/CLI language so that you can construct a vector. An additional problem is Point, your C++ declaration for it is not compatible with the managed version of it. Your code ought to resemble this, add it to a class library project from the CLR node.

#include <vector>

using namespace System;
using namespace System::Collections::Generic;

struct Point { int x; int y; };
void findNeighbors(Point p, std::vector<Point> &neighbors, double maxDist);

namespace Mumble {

    public ref class Wrapper
    {
    public:
        List<System::Drawing::Point>^ FindNeigbors(System::Drawing::Point p, double maxDist) {
            std::vector<Point> neighbors;
            Point point; point.x = p.X; point.y = p.Y;
            findNeighbors(point, neighbors, maxDist);
            List<System::Drawing::Point>^ retval = gcnew List<System::Drawing::Point>();
            for (std::vector<Point>::iterator it = neighbors.begin(); it != neighbors.end(); ++it) {
                retval->Add(System::Drawing::Point(it->x, it->y));
            }
            return retval;
        }
    };
}

Do note the cost of copying the collection, this can quickly erase the perf advantage you might get out of writing the algorithm in native C++.

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