应该是目前网上能看到的思路最清晰的版本了！
首选是CPP端，把以下编译为dll
#pragma warning(disable:4996)
#include <stdio.h>
#include <string.h>
//extern "C" __declspec(dllexport) void __stdcall init(int &num)
//{
// num = 233;
//} //OK
typedef struct Student
{
char name[20];
int age;
double scores[32];
}Student;
typedef struct Class
{
int number;
Student students[126];
}Class;
extern "C" __declspec(dllexport) int ExportClass(Class** pClass, int& num)
{
num = 50;
*pClass = new Class[num];
for (int i = 0; i < num; i++)
{
(*pClass)[i].number = i;
for (int j = 0; j < 126; j++)
{
memset((*pClass)[i].students[j].name, 0, 20);
sprintf((*pClass)[i].students[j].name, "name_%d_%d", i, j);
(*pClass)[i].students[j].age = j % 2 == 0 ? 15 : 20;
}
}
return 0;
}
extern "C" __declspec(dllexport) int ImportClass(Class* pClass, int num)
{
for (int i = 0; i < num; i++)
{
printf(" c number:%d ", pClass[i].number);
for (int j = 0; j < 126; j++)
{
printf(" name%s ",pClass[i].students[j].name);
printf(" age%d ", pClass[i].students[j].age);
}
printf("\n");
}
return 0;
}
第一个函数ExportClass：用于传入一个空指针的地址，在函数内部重新对它实例化并赋值，num为最终获取的对象个数，因为c#端是不知道的！
第二个函数ImportClass：用于传入一个C#端过来的指针，长度(num)由C#端决定，同理，这个时候CPP端也不知道指针指向数值长度
C#端：
using System.Runtime.InteropServices;
[StructLayout(LayoutKind.Sequential)]
public struct Student
{
[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 20)]
public string name;
public int age;
[MarshalAs(UnmanagedType.ByValArray, SizeConst = 32)]
public double[] scores;
}
[StructLayout(LayoutKind.Sequential)]
public struct Class
{
public int number;
[MarshalAs(UnmanagedType.ByValArray, SizeConst = 126)]
public Student[] students;
}
public class ddd
{
[DllImport("DllFoobar.dll", CallingConvention = CallingConvention.Cdecl)]
public static extern void init(ref int num);
[DllImport("DllFoobar.dll", CallingConvention = CallingConvention.Cdecl)]
public static extern int ExportClass(ref IntPtr pclasses ,ref int num);
[DllImport("DllFoobar.dll", CallingConvention = CallingConvention.Cdecl)]
public static extern int ImportClass([In, Out] Class[] classes, int num);
unsafe static void Main()
{
int num = 0;
int size = Marshal.SizeOf(typeof(Class));
IntPtr infosIntptr = IntPtr.Zero;// Marshal.AllocHGlobal(size * 50);
//Class[] infos = new Class[50];
ExportClass(ref infosIntptr,ref num);
Console.WriteLine("infosIntptr:"+ infosIntptr);
//ExportClass(classes,ref num);
for (int inkIndex = 0; inkIndex < num; inkIndex++)
{
IntPtr ptr = (IntPtr)(infosIntptr.ToInt64() + inkIndex * size);
var dd = (Class)Marshal.PtrToStructure(ptr, typeof(Class));
Console.WriteLine(dd.number+" "+dd.students[0].name);
//break;
}
Console.WriteLine("num:"+ num+ " infosIntptr:" +(infosIntptr!=IntPtr.Zero));
Marshal.FreeHGlobal(infosIntptr);
/
int c = 6;
Class[] classes=new Class[c];
for (int i = 0; i < classes.Length; i++)
{
classes[i].number = i;
classes[i].students = new Student[126];
for (int s = 0; s < 126; s++)
{
classes[i].students[s].name = "aa_dd_"+s;
classes[i].students[s].age = i + 10;
}
}
ImportClass(classes,c);
Console.ReadKey();
}
}
PS：
这里ExportClass内由于第一个参数CPP端是一个二级指针pclasses，所以对这个指针提取地址，也就是 ref IntPtr pclasses，即指向指针的指针，由于这个指针是在CPP里面实例化的，所以整活完后需要手动在C#端释放内存；
第二个函数就比较直观了，通过特殊的定义[In, Out] Class[] classes传入数值到CPP里
运行上面两个工程，最后如果是下面的界面，那么恭喜你成功了：
Ref
https://blog.csdn.net/fenggewan/article/details/88409551
https://www.jb51.net/article/103825.htm
https://blog.csdn.net/bruce135lee/article/details/80952032
