从 C# 调用包含函数指针的 DLL 函数

Question

我有一个用 C++ 编写的 DLL，其中包括导出的函数，该函数具有用作回调函数的函数指针。

// C++ 
DllExport unsigned int DllFunctionPointer( unsigned int i, unsigned int (*TimesThree)( unsigned int number ) ) {
    return TimesThree( i )  ; 
}

我有一个 CSharp 应用程序，我想用它来调用 DLL 函数。

// C#
public unsafe delegate System.UInt32 CallBack( System.UInt32 number ); 
class Program
{
    [DllImport("SimpleDLL.dll")]
    public static extern System.UInt32 DllFunctionPointer( System.UInt32 i, CallBack cb) ;

    static unsafe void Main(string[] args)
    {
        System.UInt32 j = 3;
        System.UInt32 jRet = DllFunctionPointer(j, CallBack );
        System.Console.WriteLine("j={0}, jRet={1}", j, jRet); 
    }

    static System.UInt32 CallBack( System.UInt32 number ) {
        return number * 3 ; 
    }
}

上述代码的问题是应用程序崩溃并显示以下错误消息。

'CallingACallbackFromADLL.vshost.exe' (Managed (v4.0.30319)): Loaded 'C:\XXXX\CallingACallbackFromADLL.exe', Symbols loaded.
Managed Debugging Assistant 'PInvokeStackImbalance' has detected a problem in 'C:\XXXX\CallingACallbackFromADLL.vshost.exe'.
Additional Information: A call to PInvoke function 'CallingACallbackFromADLL!CallingACallbackFromADLL.Program::DllFunction' has unbalanced the stack. This is likely because the managed PInvoke signature does not match the unmanaged target signature. Check that the calling convention and parameters of the PInvoke signature match the target unmanaged signature.

The program '[9136] CallingACallbackFromADLL.vshost.exe: Managed (v4.0.30319)' has exited with code 1073741855 (0x4000001f).

我不确定下一步该做什么。

我的问题是：

• 从 C# 应用程序调用包含回调指针的 C++ DLL 函数的正确方法是什么。

Answer 1

这是因为默认情况下，C# 中的函数调用约定是__stdcall，但在C/C++ 中默认是__cdecl，因此您应该将函数的调用约定更改如下：

[UnmanagedFunctionPointer(CallingConvention.Cdecl)]
public delegate void TimesTree( uint frame );
[DllImport("SimpleDLL.dll")]
public static extern System.UInt32 DllFunctionPointer( uint i,
    [MarshalAs(UnmanagedType.FunctionPtr)] TimesTree callback ) ;

static unsafe void Main(string[] args)
{
    // ...
    System.UInt32 jRet = DllFunctionPointer(j, CallBack );
    // ...
}