Help with strange PInvoke conversion

Hi, thanks in advance for your time and eventually for your help.

I have to wrap some c functions from a dll creating a C# assembly .
I tried many forums etc etc but i didn't find any help .

Here's the c funtion prototype :

short SessionNew( Session *pSession, SessionNewArgRec *pSessionNewArgRec );

where :

typedef struct _Session * Session ;
struct _Session is not defined anywhere, so i suppose that Session is a int ptr

SessionNewArgRec is a struct which im sure i do a good conversion of .

this is what i've written up to now :

[DllImport( "libxxx30.dll" , SetLastError = true, CallingConvention=CallingConvention.Cdecl)]
public static extern short SessionNew( IntPtr hSession, IntPtr lpSessionNewArg);

i don't think this is right, 'cause either it gives a memory violation exception, or i get an "invalid parameter" error code from the function .

here is the c sample code to help you understand what i have to do :

Session sess = NULL;
SessionNewArgRec args ;

// ... here i fill the SessionNewArgRec structure

SessionNew( &sess, &args );

PLEASE HELP ME IF YOU CAN ... im desperate ..

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Help with strange PInvoke conversion

Dhaval-Patel
Should i declare the IntPtr as IntPtr.Zero

i mean something like :

IntPtr hSessionPtr = IntPtr.Zero;

api.SessionNew( out hSessionPtr, .... );

sorry but im not a .net guru :P
NeroToxic
Yes, that way you can tell that the DLL actually gave you a session handle back, it should be non-zero after the call.
RobertFogt
Hmm, you're right, the argument is passed as struct _Session**. Try declaring the first argument as 'out IntPtr'.
xRuntime
Sigh. The other interpretation is that it actually wants to write a chunk of memory to keep the session structure. You have no idea how much memory. Give it a lot:
IntPtr hSession = Marshal.AllocHGlobal(2048);

Any luck digging up that 'C' code yet that uses this DLL
aditi shah
here's my code :

IntPtr hSession = IntPtr.Zero;

SessionNewArg args = new SessionNewArg();

// ... i fill the args structure

api.SessionNew( out hSession, args.getPtr() );

// the args.getPtr() simply returns an IntPtr to the marshalld structure

and here is the result :

Excetion : Attempted to read or write protected memory. This is often an indication that other memory is corrupt.

at xxx.api.SessionNew( IntPtr& hSession, IntPtr lpSessionNewArg)

here's the message ...

it seems that the function expects something inside hSession ...
ronnie2002c2c
There's very little hope if you don't know what struct _Session looks like. Try to find some 'C' or C++ code that calls this DLL entrypoint...
Dylan Smith
Sorry, maybe i didn't explain myself well ...

struct _Session is not defined anywhere ... im sure of this ... so the code :

typedef struct _Session * Session;

means :

typedef void * Session;

i suppose that this is some kind of a strage way to type-define a general purpose handle ... due to the fact that i really don't know how to "translate" this from c to c#, i'm getting all sort of errors from the function ...

the code :

Session sess = NULL;
SessionNewArgRec args ;

// ... here i fill the SessionNewArgRec structure

SessionNew( &sess, &args );

is the only code you need to make this work in a c/c++ applications ...
Madhu Gandhi
same exception as before ... even if i prealloc the chunk of memory ... i wrote that piece of C code, so there's nothing to dig about ... it works perfectly well in C ...
Help with strange PInvoke conversion

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