将结构从非托管C ++传递到C＃ [英] Passing struct from unmanaged C++ to C#

问题描述

注意：最后的工作解决方案是编辑之后！

Note: The final working solution is after the edit!

我希望有人能帮助我解决一个问题以解决最近几天。

I hope someone can help me with a problem I've been trying to solve for the last few days.

我试图将结构从非托管C ++ DLL传递到C＃脚本。这是我到目前为止：

I am trying to pass a struct from a unmanaged C++ DLL to a C# script. This is what I have so far:

C ++

EXPORT_API uchar *detectMarkers(...) {
    struct markerStruct {
            int id;
    } MarkerInfo;

    uchar *bytePtr = (uchar*) &MarkerInfo;

    ...

    MarkerInfo.id = 3;
    return bytePtr;
}

C＃

[DllImport ("UnmanagedDll")] 
    public static extern byte[] detectMarkers(...);

...

[StructLayout(LayoutKind.Explicit, Size = 16, Pack = 1)]
public struct markerStruct
{
    [MarshalAs(UnmanagedType.U4)]
    [FieldOffset(0)]
    public int Id;
}

...

markerStruct ByteArrayToNewStuff(byte[] bytes){
    GCHandle handle = GCHandle.Alloc(bytes, GCHandleType.Pinned);
    markerStruct stuff = (markerStruct)Marshal.PtrToStructure(
        handle.AddrOfPinnedObject(), typeof(markerStruct));
    handle.Free();
    return stuff;
}

...

print(ByteArrayToNewStuff (detectMarkers(d, W, H, d.Length) ).Id);

问题是这样工作，但打印的值完全关闭有时候最大的int值）。

The problem is that this works, but the value printed is completely off (sometimes it prints around 400, sometimes max int value).

我猜想有一些问题，我如何编组C＃中的结构。任何想法？

I'm guessing that there's something wrong with how I marshalled the struct in C#. Any ideas?

编辑：

C ++

struct markerStruct {
    int id;
};

...

EXPORT_API void detectMarkers( ... , markerStruct *MarkerInfo) {
    MarkerInfo->id = 3;
    return;
}

C＃

[DllImport ("ArucoUnity")] 
    public static extern void detectMarkers( ... ,
        [MarshalAs(UnmanagedType.Struct)] ref MarkerStruct markerStruct);

...

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi, Pack = 1)]
public struct MarkerStruct
{
    public int Id;
}

...

detectMarkers (d, W, H, d.Length, ref markerInfo);      
print( markerInfo.Id );

推荐答案

您返回一个指向局部变量的指针已经被销毁之前.NET可以读取它。这是一个坏主意在纯C ++和一个坏主意与p / invoke。

You're returning a pointer to a local variable which has already been destroyed before .NET can read it. That's a bad idea in pure C++ and a bad idea with p/invoke.

而是，有C＃传递一个结构的指针（只是使用 ref 关键字）和C ++代码只是填充它。

Instead, have C# pass a pointer to a structure (just use the ref keyword) and the C++ code just fill it in.

这篇关于将结构从非托管C ++传递到C＃的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！