我需要在dll中调用一个函数并返回一个结构数组。我事先并不知道阵列的大小。如何才能做到这一点?错误can not marshal 'returns value' invalid managed / unmanaged
C#中的代码:
[DllImport("CppDll"]
public static extern ResultOfStrategy[] MyCppFunc(int countO, Data[] dataO, int countF, Data[] dataF);
在C ++中:
extern "C" _declspec(dllexport) ResultOfStrategy* WINAPI MyCppFunc(int countO, MYDATA * dataO, int countF, MYDATA * dataF)
{
return Optimization(countO, dataO, countF, dataF);
}
返回struct的数组:
struct ResultOfStrategy
{
bool isGood;
double allProfit;
double CAGR;
double DD;
int countDeals;
double allProfitF;
double CAGRF;
double DDF;
int countDealsF;
Param Fast;
Param Slow;
Param Stop;
Param Tp;
newStop stloss;
};
答案 0 :(得分:5)
我会给你两个回复。第一个是非常基本的方法。第二个是非常先进的。
假设:
C-侧:
struct ResultOfStrategy
{
//bool isGood;
double allProfit;
double CAGR;
double DD;
int countDeals;
double allProfitF;
double CAGRF;
double DDF;
int countDealsF;
ResultOfStrategy *ptr;
};
C#侧的:
public struct ResultOfStrategy
{
//[MarshalAs(UnmanagedType.I1)]
//public bool isGood;
public double allProfit;
public double CAGR;
public double DD;
public int countDeals;
public double allProfitF;
public double CAGRF;
public double DDF;
public int countDealsF;
public IntPtr ptr;
}
请注意,我删除了bool
,因为它在案例2中存在一些问题(但它适用于案例1)......现在......
案例1非常基础,它将导致.NET编组程序将C中内置的数组复制到C#数组。
我编写的案例2非常先进,它试图绕过这个marshal-by-copy并使C和.NET可以共享相同的内存。
为了检查差异,我写了一个方法:
static void CheckIfMarshaled(ResultOfStrategy[] ros)
{
GCHandle h = default(GCHandle);
try
{
try
{
}
finally
{
h = GCHandle.Alloc(ros, GCHandleType.Pinned);
}
Console.WriteLine("ros was {0}", ros[0].ptr == h.AddrOfPinnedObject() ? "marshaled in place" : "marshaled by copy");
}
finally
{
if (h.IsAllocated)
{
h.Free();
}
}
}
我在ptr
添加了一个struct
字段,其中包含struct
(C端)的原始地址,以查看它是否已被复制或是否已被复制是原始struct
。
案例1:
C-侧:
__declspec(dllexport) void MyCppFunc(ResultOfStrategy** ros, int* length)
{
*ros = (ResultOfStrategy*)::CoTaskMemAlloc(sizeof(ResultOfStrategy) * 2);
::memset(*ros, 0, sizeof(ResultOfStrategy) * 2);
(*ros)[0].ptr = *ros;
(*ros)[0].allProfit = 100;
(*ros)[1].ptr = *ros + 1;
(*ros)[1].allProfit = 200;
*length = 2;
}
和C#-side:
public static extern void MyCppFunc(
[MarshalAs(UnmanagedType.LPArray, ArraySubType = UnmanagedType.Struct, SizeParamIndex = 1)] out ResultOfStrategy[] ros,
out int length
);
然后:
ResultOfStrategy[] ros;
int length;
MyCppFunc(out ros, out length);
Console.Write("Case 1: ");
CheckIfMarshaled(ros);
ResultOfStrategy[] ros2;
.NET封送程序知道(因为我们给它提供了信息)第二个参数是out ResultOfStrategy[] ros
的长度(参见SizeParamIndex
?),因此可以创建一个.NET数组和从C分配的数组中复制数据。请注意,在C代码中,我使用::CoTaskMemAlloc
来分配内存。 .NET 想要使用该分配器分配的内存,因为它随后释放它。如果你使用malloc
/ new
/ ???分配ResultOfStrategy[]
内存,会发生不好的事情。
案例2:
C-侧:
__declspec(dllexport) void MyCppFunc2(ResultOfStrategy* (*allocator)(size_t length))
{
ResultOfStrategy *ros = allocator(2);
ros[0].ptr = ros;
ros[1].ptr = ros + 1;
ros[0].allProfit = 100;
ros[1].allProfit = 200;
}
C#侧的:
// Allocator of T[] that pins the memory (and handles unpinning)
public sealed class PinnedArray<T> : IDisposable where T : struct
{
private GCHandle handle;
public T[] Array { get; private set; }
public IntPtr CreateArray(int length)
{
FreeHandle();
Array = new T[length];
// try... finally trick to be sure that the code isn't interrupted by asynchronous exceptions
try
{
}
finally
{
handle = GCHandle.Alloc(Array, GCHandleType.Pinned);
}
return handle.AddrOfPinnedObject();
}
// Some overloads to handle various possible length types
// Note that normally size_t is IntPtr
public IntPtr CreateArray(IntPtr length)
{
return CreateArray((int)length);
}
public IntPtr CreateArray(long length)
{
return CreateArray((int)length);
}
public void Dispose()
{
FreeHandle();
}
~PinnedArray()
{
FreeHandle();
}
private void FreeHandle()
{
if (handle.IsAllocated)
{
handle.Free();
}
}
}
[UnmanagedFunctionPointer(CallingConvention.Cdecl)]
public delegate IntPtr AllocateResultOfStrategyArray(IntPtr length);
[DllImport("CplusPlusSide.dll", CallingConvention = CallingConvention.Cdecl)]
public static extern void MyCppFunc2(
AllocateResultOfStrategyArray allocator
);
然后
ResultOfStrategy[] ros;
using (var pa = new PinnedArray<ResultOfStrategy>())
{
MyCppFunc2(pa.CreateArray);
ros = pa.Array;
// Don't do anything inside of here! We have a
// pinned object here, the .NET GC doesn't like
// to have pinned objects around!
Console.Write("Case 2: ");
CheckIfMarshaled(ros);
}
// Do the work with ros here!
现在这个很有趣...... C函数从C#-side(函数指针)接收一个分配器。此分配器将分配length
个元素,然后必须记住分配的内存的地址。这里的诀窍是C#-side我们分配C所需大小的ResultOfStrategy[]
,然后直接用于C-side。如果ResultOfStrategy
不是blittable(这个术语意味着你只能在ResultOfStrategy
中使用某些类型,主要是数字类型,没有string
,没有char
,这将会严重破坏,没有bool
,请参阅here)。代码是非常先进的,因为除此之外,它必须使用GCHandle
来固定.NET数组,以便它不会被移动。处理此GCHandle
非常复杂,因此我必须创建一个ResultOfStrategyContainer
IDisposable
。在这个类中,我甚至保存对创建的数组的引用(ResultOfStrategy[] ResultOfStrategy
)。请注意using
的使用。这是使用该类的正确方法。
bool
和案例2
正如我所说,虽然bool
与案例1合作,但它们不适用于案例2 ......但我们可以作弊:
C-侧:
struct ResultOfStrategy
{
bool isGood;
C#侧的:
public struct ResultOfStrategy
{
private byte isGoodInternal;
public bool isGood
{
get => isGoodInternal != 0;
set => isGoodInternal = value ? (byte)1 : (byte)0;
}
这有效:
C-侧:
extern "C"
{
struct ResultOfStrategy
{
bool isGood;
double allProfit;
double CAGR;
double DD;
int countDeals;
double allProfitF;
double CAGRF;
double DDF;
int countDealsF;
ResultOfStrategy *ptr;
};
int num = 0;
int size = 10;
__declspec(dllexport) void MyCppFunc2(ResultOfStrategy* (*allocator)(size_t length))
{
ResultOfStrategy *ros = allocator(size);
for (int i = 0; i < size; i++)
{
ros[i].isGood = i & 1;
ros[i].allProfit = num++;
ros[i].CAGR = num++;
ros[i].DD = num++;
ros[i].countDeals = num++;
ros[i].allProfitF = num++;
ros[i].CAGRF = num++;
ros[i].DDF = num++;
ros[i].countDealsF = num++;
ros[i].ptr = ros + i;
}
size--;
}
}
C#侧的:
[StructLayout(LayoutKind.Sequential)]
public struct ResultOfStrategy
{
private byte isGoodInternal;
public bool isGood
{
get => isGoodInternal != 0;
set => isGoodInternal = value ? (byte)1 : (byte)0;
}
public double allProfit;
public double CAGR;
public double DD;
public int countDeals;
public double allProfitF;
public double CAGRF;
public double DDF;
public int countDealsF;
public IntPtr ptr;
}
然后
ResultOfStrategy[] ros;
for (int i = 0; i < 10; i++)
{
using (var pa = new PinnedArray<ResultOfStrategy>())
{
MyCppFunc2(pa.CreateArray);
ros = pa.Array;
// Don't do anything inside of here! We have a
// pinned object here, the .NET GC doesn't like
// to have pinned objects around!
}
for (int j = 0; j < ros.Length; j++)
{
Console.WriteLine($"row {j}: isGood: {ros[j].isGood}, allProfit: {ros[j].allProfit}, CAGR: {ros[j].CAGR}, DD: {ros[j].DD}, countDeals: {ros[j].countDeals}, allProfitF: {ros[j].allProfitF}, CAGRF: {ros[j].CAGRF}, DDF: {ros[j].DDF}, countDealsF: {ros[j].countDealsF}");
}
Console.WriteLine();
}