Structures in C#

[darwen]

Sorry, I don't understand your last post.

If you pass bDOJB as "22/01/2009" then it's a string right ?

Or is there some kind of encoding which is used in C++ to turns the date 22/01/2009 into an unsigned char buffer ?

Can you show the C++ code for doing this ?

Darwen.

[cheery_poori]

Hello Darwen,

I will explain in detail..

I have created a DLL Which has the following structure

struct EmpDetails
{
unsigned char * bNAME;
unsigned char * bAGE;
unsigned char * bDOJ;
unsigned char * bDESIGNATATION;
unsigned char * bGENDER;
unsigned char * bSALARY;

};

and a Function to which the above said structure is passed as input the function signature is as follows:

int __stdcall FnWriteEmpDetails(const EmpDetails &stEmpDtls, unsigned char * bReturnVal);

Here, the bReturnval is an output parameter there is no problem with this..

So now i want to use the DLL in C# application.
I have done a Wrapper Class in C# for the DLL.

The structure in c# looks like below:

public struct EmpDetails
{
[MarshalAs(UnmanagedType.LPStr)]
public string bNAME;

[MarshalAs(UnmanagedType.LPStr)]
public string bAGE;

[MarshalAs(UnmanagedType.LPStr)]
public string bDOJ;

[MarshalAs(UnmanagedType.LPStr)]
public string bDESIGNATATION;

[MarshalAs(UnmanagedType.LPStr)]
public string bGENDER;

[MarshalAs(UnmanagedType.LPStr)]
public string bSALARY;

};

And the function signature in C# is

[DllImport("TEST_DLL.dll")]
//int __stdcall FnWriteEmpDetails( const EmpDetails &stEmpDetails, unsigned char * bReturnVal);
public static extern int FnWriteEmpDetails(ref EmpDetails stEmpDetails, byte[] bReturnVal);


The DLL function internally just takes the input provided and send it to some device, here the data needs to be sent in bytes,

iCount = strlen((char*)stEmpDetails.bDOJ);
for(i, j=0; j< (iCount+1); j++,i++)
bData[i] = stEmpDetails.bDOJ[j];

so if i pass the bDOJ as string "22/1/2009" incorrect data will be taken. I want to the day as "22" in one byte.

I hope i have explained the problem properly...

Thanks & Regards,
Poornima .S

[darwen]

Please use code tags in future.

Try this for the struct :

using System.Runtime.InteropServices;

public struct EmpDetails
{
    [MarshalAs(UnmanagedType.LPStr)]
    public string bNAME;

    [MarshalAs(UnmanagedType.LPStr)]
    public string bAGE;

    public IntPtr bDOJ;

    [MarshalAs(UnmanagedType.LPStr)]
    public string bDESIGNATATION;

    [MarshalAs(UnmanagedType.LPStr)]
    public string bGENDER;

    [MarshalAs(UnmanagedType.LPStr)]
    public string bSALARY;
};

// code to translate byte [] to bDObj

byte [] byteArray = new byte[4];
GCHandle handle = GCHandle.Alloc(byteArray, GCHandleType.Pinned);

try
{
    EmpDetails empDetails = new EmpDetails();
    empDetails.bDOJ = handle.AddrOfPinnedObject();
    // make function call
}
finally
{
    handle.free();
}

Usually I'd have bDOJ as a byte [] array in the struct, but since you have to pass it by reference I don't believe this will work. P/Invoke will try to marshal the byte [] array from native to managed code on the way out of the function which it can't do because it doesn't know how big it is. So P/Invoke will most probably throw an exception at this point.

Darwen.