NET 4.0与DLL一起使用时出现未知错误

Question

c++ code is

MSIPC_SDK LONG __stdcall Ms_IpcClient_CaptureImage(LONG nUserId, char *sFilePath, 
    int nPathLen, const char *sDiskPath = NULL);//sDiskPath example: "C: \\".

Affect: Take a snapshoot

Parameters remark:

• LONG nUserId : Ms_Ipc_Login()//Return value after login successfully
• char *sFilePath : //destination for saving the recording files
• int nPathLen : //the length of the path
• const char *sDiskPath = NULL : //which disk to be saved

my c# code is:

[DllImport("MsIpcSDK", CharSet = CharSet.Ansi, 
    CallingConvention = CallingConvention.StdCall)]
public static extern int Ms_IpcClient_CaptureImage(
    int lUserID, 
    [MarshalAs(UnmanagedType.LPStr)]
    string sFilePath, 
    int nPathLen,
    [MarshalAs(UnmanagedType.LPStr)]
    string sDiskPath
);

and using is method:

var ret = Ms_IpcClient_CaptureImage(loginID, "C:\\a.bmp", 10000, "C:\\");

It is working in .Net Framework 2 but does not work in .Net Framework 4. How can I fix it in .Net Framework 4?

Answer 1

sFilePath is used to pass a string from callee to caller. That's why the type is char* rather than const char* , and that's why there is a parameter for buffer length. That means you need to use StringBuilder rather than string . The p/invoke should be:

[DllImport("MsIpcSDK", CharSet = CharSet.Ansi, 
    CallingConvention = CallingConvention.StdCall)]
public static extern int Ms_IpcClient_CaptureImage(
    int lUserID, 
    StringBuilder sFilePath, 
    int nPathLen,
    string sDiskPath
);

And the call should be:

var filePath = new StringBuilder(260);
var ret = Ms_IpcClient_CaptureImage(loginID, filePath, filePath.Capacity, "C:\\");

Your code has always been wrong and you've just been getting away with it up until now. The fact that you passed a made up buffer length value of 10000 should have set the alarm bells ringing!