在C＃中封送非托管變量

Question

我正在C＃代碼上導入非托管dll。 .h文件描述了如下所示的方法

DLL_API int __stdcall SetConfiguration(IN char* configuration);

DLL_API int  __stdcall GetErrorMessage_UTF16(
    INOUT int* errorGroup, 
    INOUT char* errorCode, /*It must be allocated by the caller and its length must be at least 10 bytes, otherwise the function will crash*/
    INOUT wchar_t *messageText, 
    IN int bufferLength);

我設法調用SetConfiguration方法

[DllImport(DllPath, CharSet = CharSet.Ansi, CallingConvention = CallingConvention.StdCall)]
private static extern int SetConfiguration([In] MarshalAs(UnmanagedType.LPStr)] string configuration);

提供一個簡單的C＃字符串即可完成工作。

現在，我正在嘗試GetErrorMessage_UTF16方法，但沒有成功。 那么，如何分配errorCode的長度以及如何聲明wchar_t * messageText變量？

我已經嘗試過類似的方法，但是它似乎不起作用

[DllImport(DllPath, CharSet = CharSet.Ansi, CallingConvention = CallingConvention.StdCall)]
private static extern int GetErrorMessage_UTF16(
    [In, Out] int errorGroup, 
    [In, Out] [MarshalAs(UnmanagedType.LPStr)] string errorCode, 
    [In, Out] [MarshalAs(UnmanagedType.LPStr)] StringBuilder messageText, 
    [In] int bufferLength);

無論我嘗試了什么

Exception thrown at 0x0f5d1235 (Mydll.dll) in Mydll.exe: 0xc0000005: Access violation writing location 0x067d1000

If there is a handler for this exception, the program may be safely continued.

Answer 1

好，我找到了答案

[DllImport(DllName, EntryPoint = "GetErrorMessage_UTF16", CharSet = CharSet.Ansi, CallingConvention = CallingConvention.StdCall)]
public static extern int GetErrorMessage_UTF16(out int errorGroup, IntPtr errorCode, IntPtr messageText, int bufferLength);

為errorCode和messageText創建一個指針，然后分配大小。

IntPtr errorCode = Marshal.AllocHGlobal(10);
IntPtr messageText = Marshal.AllocHGlobal(someBufferLength * sizeof(char));

當不需要變量時，不要忘記釋放分配的空間。