问题描述
你们能帮我解决以下问题吗?我有一个 C++ 函数 dll,它将被另一个 C# 应用程序调用.我需要的功能之一如下:
Could you guys please help me solve the following issue?I have a C++ function dll, and it will be called by another C# application.One of the functions I needed is as follow:
struct DataStruct
{
unsigned char* data;
int len;
};
DLLAPI int API_ReadFile(const wchar_t* filename, DataStruct** outData);
我用 C# 编写了以下代码:
I wrote the following code in C#:
class CS_DataStruct
{
public byte[] data;
public int len;
}
[DllImport("ReadFile.dll", CallingConvention = CallingConvention.Cdecl, CharSet = CharSet.Unicode)]
private static extern int API_ReadFile([MarshalAs(UnmanagedType.LPWStr)]string filename, ref CS_DataStruct data);
不幸的是,上面的代码不起作用......我猜这是由于 C++ func 需要一个指向 DataStruct 的指针,而我刚刚传入了一个 CS_DataStruct 的引用.
Unfortunately, the above code is not working... I guess that is due to the C++ func takes a pointer-to-pointer of DataStruct, while I just passed a reference of CS_DataStruct in.
我可以知道如何将指针到指针传递给 C++ func 吗?如果不可能,有什么解决方法吗?(C++ API 是固定的,因此无法将 API 更改为指针)
May I know how can I pass a pointer-to-pointer to the C++ func? If it is not possible, is there any workaround? (the C++ API is fixed, so changing API to pointer is not possible)
DataStruct 的内存将由 c++ 函数分配.在此之前,我不知道数据数组应该有多大.(感谢下方的评论)
Memory of DataStruct will be allocated by c++ function. Before that, I have no idea how large the data array should be.(Thanks for the comments below)
推荐答案
我使用了以下测试实现:
I used the following test implementation:
int API_ReadFile(const wchar_t* filename, DataStruct** outData)
{
*outData = new DataStruct();
(*outData)->data = (unsigned char*)_strdup("hello");
(*outData)->len = 5;
return 0;
}
void API_Free(DataStruct** pp)
{
free((*pp)->data);
delete *pp;
*pp = NULL;
}
访问这些函数的 C# 代码如下:
The C# code to access those functions are as follows:
[StructLayout(LayoutKind.Sequential)]
struct DataStruct
{
public IntPtr data;
public int len;
};
[DllImport("ReadFile.dll", CallingConvention = CallingConvention.Cdecl, CharSet = CharSet.Unicode)]
unsafe private static extern int API_ReadFile([MarshalAs(UnmanagedType.LPWStr)]string filename, DataStruct** outData);
[DllImport("ReadFile.dll", CallingConvention = CallingConvention.Cdecl)]
unsafe private static extern void API_Free(DataStruct** handle);
unsafe static int ReadFile(string filename, out byte[] buffer)
{
DataStruct* outData;
int result = API_ReadFile(filename, &outData);
buffer = new byte[outData->len];
Marshal.Copy((IntPtr)outData->data, buffer, 0, outData->len);
API_Free(&outData);
return result;
}
static void Main(string[] args)
{
byte[] buffer;
ReadFile("test.txt", out buffer);
foreach (byte ch in buffer)
{
Console.Write("{0} ", ch);
}
Console.Write("
");
}
数据现在安全地传输到buffer
,应该没有内存泄漏.我希望它会有所帮助.
The data is now transferred to buffer
safely, and there should be no memory leaks. I wish it would help.
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