如何从功能和全局变量从C ++ DLL在C＃中返回数组？ [英] How to get return array from function with global variable from C++ dll in C#?

问题描述

我有一个用C编写的dll文件++（文件名是DllForTest.dll），这是它的代码：

I have a dll file which is written by C++ (the name of file is "DllForTest.dll"), this is its code:

#include "stdafx.h"
#include <vector>
using namespace std;

double *ret;
double* _stdcall f(int* n)
{
    vector<double> vret;
    int i=0;
    do
    {
        vret.push_back(i);
        i++;
    } while (the condition to stop this loop);
    *n=i;
    ret = new double[*n];
    for (i=0;i<*n;i++)
        ret[i]=vret[i];
    return ret;
}

这是C＃代码来调用f函数从DLL文件上面得到回报值：

This is C# code to call f function from the dll file above to get return value:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Runtime.InteropServices;

namespace WindowForm
{
    public partial class Form1 : Form
    {
        [DllImport("DllForTest.dll")]
        public static extern double[] f(ref int n);

        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            int n=0;
            double[] x;
            x = f(ref n);
            MessageBox.Show("x[0]= " + x[0]);
        }
    }
}

当我运行时，它产生错误：

When I run, it generate an error:

无法元帅返回值：无效的托管/非托管类型组合

Cannot marshal 'return value': Invalid managed/unmanaged type combination.

如何解决它来获得想要的结果呢？谢谢你。

How to fix it to gain wanted result? Thanks.

推荐答案

尝试指定返回值的IntPtr 而不是<$的C $ C>双[] ，然后用 Marshal.Copy 从这个IntPtr的数据复制到你的双[]数组：

Try specifying return value as IntPtr instead of double[] and then use Marshal.Copy to copy data from this IntPtr to your double[] array:

[DllImport("DllForTest.dll")]
static extern IntPtr f(ref int n);

private void button1_Click(object sender, EventArgs e)
{
    int n=0;

    IntPtr intPtr = f(ref n);
    double[] x = new double[n];
    Marshal.Copy(intPtr, x, 0, n);

    MessageBox.Show("x[0]= " + x[0]);
}

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