在 C++ 和 C# ByRef 之间传递字节数组会引发 AccessViolationException
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Passing byte array between C++ and C# ByRef raises AccessViolationException
提问by anonim
I am trying to create a Win32 DLL exposes some functions which are called in C# as follows
我正在尝试创建一个 Win32 DLL 公开一些在 C# 中调用的函数，如下所示
__declspec(dllexport) int GetData(unsigned char* *data, int* size)
{
try
{
int tlen = 3;
unsigned char* tchr = new unsigned char[5];
tchr[0] = 'a';
tchr[1] = 'b';
tchr[2] = 'c';
*size = tlen;
*data = tchr;
return 1;
}
catch (char *p)
{
return 0;
}
}
And on C# side
在 C# 方面
[DllImport("MyDll.dll")]
static extern int GetData(ref byte[] data, ref int size);
static void Main()
{
try
{
int hr = 0;
byte[] gData = null;
int gSize = 0;
hr = GetData(ref gData, ref gSize);
Console.WriteLine(gSize);
for (int i = 0; i < gSize; i++)
Console.WriteLine((char)gData[i]);
}
catch (Exception p)
{
Console.WriteLine(p.ToString());
}
}
When I run C# code, AccessViolationExceptionhappens on GetDatafunction which is a sign of exception in C++ code however, following C++ code snippet works fine without any error.
当我运行 C# 代码时，AccessViolationException发生在GetData函数上，这是 C++ 代码中的异常标志，但是，遵循 C++ 代码片段工作正常，没有任何错误。
int _tmain(int argc, _TCHAR* argv[])
{
unsigned char* data = NULL;
int size = NULL;
GetData(&data, &size);
printf("%d", size);
for (int i = 0; i < size; i++)
printf("%c,", data[i]);
return 0;
}
If you compare C# mainfunction and C++ _tmain, they are almost analoguous so where I may make a mistake?
如果您比较 C#main函数和 C++ _tmain，它们几乎是类似的，所以我可能会出错？
采纳答案by David Heffernan
You are returning an array allocated by a call to C++ new and hoping that the marshaler will turn it into a C# byte[]. That won't happen.
您正在返回一个通过调用 C++ new 分配的数组，并希望封送拆收器将其转换为 C# byte[]。那不会发生。
You'll need to pass a pointer by reference and then marshal it by hand. Your p/invoke should look like this:
您需要通过引用传递一个指针，然后手动对其进行编组。您的 p/invoke 应如下所示：
[DllImport("MyDll.dll")]
static extern int GetData(out IntPtr data, out int size);
When the function returns data will point to the array and you can read the contents using the Marshal class. I guess you would copy it to a new byte array.
当函数返回数据时，数据将指向数组，您可以使用 Marshal 类读取内容。我猜你会把它复制到一个新的字节数组中。
var arr = new byte[size];
Marshal.Copy(data, arr, 0, size);
Some other points:
其他几点：
- The calling conventions do not match. The native side is cdecl and the managed is stdcall.
- You'll need to export a deallocator to delete the memory returned by the native function. Consider a re-design where the caller allocates the buffer.
- 调用约定不匹配。本机端是 cdecl，托管端是 stdcall。
- 您需要导出一个解除分配器来删除本机函数返回的内存。考虑调用者分配缓冲区的重新设计。
