指针的std :: array或std :: vector [英] std::array or std::vector from pointer

问题描述

我在C ++ / CLI数组中有一个数据数组，可以使用 pin_ptr< T> 传递给本机函数，到目前为止没有问题。但是，现在，我需要将该数组传递给C ++ / STL函数，该函数需要一个容器，例如 std :: array 或 std ::向量。

I have an array of data in a C++/CLI array that I can pass to a native function using pin_ptr<T>, no problem so far. Now, however, I need to pass the array on to a C++/STL function that expects a container such as std::array or std::vector.

最简单的方法（我首先做过）是逐个元素地复制。

The easy way of doing this (which I did first), is to copy element by element.

第二种最简单的方法是调用 std :: copy（），请参见以下问题的答案：将System :: array转换为std :: vector 。

The second-easiest way is to call std::copy(), see the answer to this question: convert System::array to std::vector.

但是，我想跳过整个复制步骤，而只使用指针。看到 std :: array 需要一个模板参数来确定其长度，我无法在运行时创建一个（但如果我输入错了，请更正我）。有没有一种方法可以创建矢量或其他类型的STL容器，而无需不必要的数据复制？

However, I want to skip the entire copying step and just use the pointer instead. Seeing as std::array requires a template argument to determine its length, I can't create one at runtime (but please do correct me if I'm wrong). Is there a way to create a vector or a different type of STL container, without unnecessary copying of data?

推荐答案

由于C + +20有一种方法可以将c ++容器与c ++ / cli中的托管数组一起使用，避免复制数据： std :: span

Since C++20 there is a way to use c++ containers with managed arrays in c++/cli that avoids copying the data: std::span

在c ++ 20中，可以使用 std :: span 包装托管的c ++ / cli数组。然后，它可以与标准容器算法一起使用。

In c++20 it's possible to use std::span to wrap a managed c++/cli array. Then it can be used with standard container algorithms.

不幸的是，Microsoft不支持c ++ / cli而不是c ++ 17。因此，必须先将指针和长度传递给另一个使用c ++ latest编译的源文件中的函数，同时使用较早的c ++ 17 / cli编译调用方的源文件。幸运的是，ABI是兼容的。可以在Visual Studio 2019的属性页中为每个文件轻松设置。

Unfortunately, Microsoft doesn't support c++/cli beyond c++17. Consequently one must first pass the pointer and length to a function in a different source file that is compiled using c++latest while compiling the caller's source file using the earlier c++17/cli. Fortunately the ABIs are compatible. This is easily set up for each file in the properties page of Visual Studio 2019.

下面是一些示例代码，它们创建了一个小的托管 array< double> 然后调用一个函数，该函数使用 std :: span 包装托管数据，然后使用 std :: sort

Here's some sample code that creates a small managed array<double> then calls a function that wraps the managed data with std::span then sorts with std::sort

// file1.cpp compile with /cli
#include <iostream>
using namespace System;
void sortme(double *p, int len);

int main()
{
    array<double>^ v = gcnew array<double> {1.0, 3.0, 2.0, 4.0};
    pin_ptr<double> pin=&v[0];
    int len=v->Length;
    sortme(pin, len);
    for (int i = 0; i < len; i++)
        std::cout << v[i] << "\n";  // prints sorted array
 }

// file2.cpp compile with c++latest
#include <span>
#include <algorithm>
void sortme(double *p, int len)
{
    std::span data_clr(p, len);
    std::sort(data_clr.begin(), data_clr.end());
}

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