从c＃中的非托管c ++ dll获取字节数组的指针 [英] get pointer on byte array from unmanaged c++ dll in c#

问题描述

c ++中有这样的功能

  externC_declspec（dllexport）uint8 * bufferOperations（uint8 * incoming，int大小）
  

我正在尝试从c＃这样调用它

  [DllImport（MagicLib.DLL，CallingConvention = CallingConvention.Cdecl）] 
 // [return：MarshalAs（UnmanagedType.ByValArray）] //， ArraySubType = UnmanagedType.SysUInt）] 
 public static extern byte [] bufferOperations（byte [] incoming，int size）; 
  

但是我得到
无法编组'返回值'：无效的管理/非托管类型组合

（（问题是 - 如何组织这个正确？
感谢阅读我的问题

解决方案

byte []是一个具有已知长度的.Net数组类型，您无法编写字节*，因为.Net不知道输出数组的长度，应该尝试手动编组将字节[]替换为字节*，然后执行以下操作：

  [DllImport（MagicLib.DLL CallingConvention = CallingConvention.Cdecl）] 
 public static extern byte * bufferOperations（byte * incoming，int size）; 
 
 public void TestMethod（）
 {
 var incoming = new byte [100]; 
 fixed（byte * inBuf = incoming）
 {
 byte * outBuf = bufferOperations（inBuf，incoming.Length）; 
 //假设返回相同的缓冲区，只有数据更改。
 //或任何其他意味着获得真正的输出缓冲区长度（例如，从图书馆文件等）。 （int i = 0; i< incoming.Length; i ++）
 incoming [i] = outBuf [i]; 
 
} 
} 
  

in c++ I have such function

extern "C" _declspec(dllexport) uint8* bufferOperations(uint8* incoming, int size)

I am trying to call it from c# like this

[DllImport("MagicLib.DLL", CallingConvention = CallingConvention.Cdecl)]
//[return: MarshalAs(UnmanagedType.ByValArray)]//, ArraySubType=UnmanagedType.SysUInt)]
public static extern byte[] bufferOperations(byte[] incoming, int size);

But I get the Cannot marshal 'return value': Invalid managed/unmanaged type combination

((( The question is - how to marshal this correctly? Thanks for reading my question

解决方案

byte[] is a .Net array type with known length. You can't marshal byte* to it, because .Net does not know the length of output array. You should try manual marshalling. Replace byte[] with byte*. Then, do like this:

[DllImport("MagicLib.DLL", CallingConvention = CallingConvention.Cdecl)]
public static extern byte* bufferOperations(byte* incoming, int size);

public void TestMethod()
{
    var incoming = new byte[100];
    fixed (byte* inBuf = incoming)
    {
        byte* outBuf = bufferOperations(inBuf, incoming.Length);
        // Assume, that the same buffer is returned, only with data changed.
        // Or by any other means, get the real lenght of output buffer (e.g. from library docs, etc).
        for (int i = 0; i < incoming.Length; i++)
            incoming[i] = outBuf[i];
    }
}

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