如何使用的PInvoke为C结构数组指针到C＃

问题描述：

我想使用的PInvoke马歇尔结构数组另一个结构中从C到C＃。据我所知，没有做不到的。结果
所以取而代之，在C结构，我宣布一个PTR我的数组，malloc的。问题：1）如何申报在C＃端的等效？ 2）我如何分配和使用的C＃侧相同呢？

I am trying to use pinvoke to marshall an array of structures inside another structure from C to C#. AFAIK, no can do.
So instead, in the C structure I declare a ptr to my array, and malloc. Problems: 1) How do I declare the equivalent on the C# side? 2) How do I allocate and use the equivalent on the C# side?

//The C code
typedef struct {
       int a;
       int b; } A;
typedef struct {
      int c;
      // A myStruct[100];    // can't do this, so:
      A *myStruct; } B;

//The c# code:
[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
public class A{
    int a;
    int b;
}

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
public class B{
      int c;
      // can't declare array of [100] A structures...
     ?
 }

：不知怎的，我misinter preTED我读到关于C＃端对象数组固定别处。
我的可以的固定在C数组的大小所以编好了，但后来我开始使用时，对象引用不设置到对象的实例：

: Somehow I misinterpreted what I read elsewhere about fixed array of objects on the c# side. And I can fix the array size in C So compiled ok, but then I get "object reference not set to an instance of an object" when using:

data.B [3]。一个= 4567; 所以，在阅读什么这个错误可能是在其他地方，我添加了此方法：

data.B[3].a = 4567; So, reading elsewhere about what this error might be, I added this method:

public void initA()
        {
          for (int i = 0; i < 100; i++) { B[i] = new A(); }
        }

再次编译OK，但同样的错误味精。

Again, compiled OK, but same error msg.

答

要名帅这样的C和C＃之间的复杂的结构，你有两个选择。

To marshal "complex" structures like this between C and C#, you have a couple of options.

在这种情况下，我会强烈建议您尝试嵌入固定数组到C端结构，因为它简化了C＃侧很多。您可以使用的MarshalAs 属性告诉C＃它需要多大的空间，在运行时在阵列中分配：

In this case, I would highly recommend that you try to embed a fixed array into your C-side structure, as it will simplify the C# side a lot. You can use the MarshalAs attribute to tell C# how much space it needs to allocate in the array at run-time:

// In C:
typedef struct
{
 int a;
 int b;
} A;

typedef struct
{
 int c;
 A data[100];
} B;

// In C#:
[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
public struct A 
{
  int a;
  int b;
}

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
public struct B
{
  int c;
  [MarshalAs(UnmanagedType.LPArray, SizeConst=100)]
  A[] data = new data[100];
}

如果你不知道，或者不能指定，为你的阵列固定的大小，那么你需要做的你做了什么，并宣布它作为C.指针在这种情况下，你不能告诉C＃阵列多少内存会在运行时使用，所以你pretty多坚持了手工做的所有编组。 This问题有如何工作的一个很好的破败，但其基本思想是：

If you don't know, or can't specify, a fixed size for your array, then you'll need to do what you did and declare it as a pointer in C. In this case, you cannot tell C# how much memory the array is going to use at run-time, so you're pretty much stuck with doing all of the marshalling by hand. This question has a good rundown of how that works, but the basic idea is:

您应该一个字段添加到您的结构，包括数组元素的计数（这会让你的生活变得更轻松）

声明领域的C＃为： IntPtr的数据; 有没有属性

使用 Marshal.SizeOf（typeof运算（A））来获得在非托管内存结构的大小。

使用 Marshal.PtrToStructure 到一个非托管结构转换为C＃

使用 IntPtr.Add（PTR，sizeofA）移动到下一个结构数组中

循环，直到你用完了。

You should add a field to your structure that includes a count of the array elements (this will make your life much easier)
Declare the field in C# as: IntPtr data; with no attributes.
Use Marshal.SizeOf(typeof(A)) to get the size of the struct in unmanaged memory.
Use Marshal.PtrToStructure to convert a single unmanaged structure to C#
Use IntPtr.Add(ptr, sizeofA) to move to the next structure in the array
Loop until you run out.

如何使用的PInvoke为C结构数组指针到C＃

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