Hi
I have faced one problem on calling the native dll's functions from C# .Net coding.Actually i wrote
one dll to control the Digital Multimeter in a remote programming mode through GPIB interface.
Initially i have imported the win32 dll provided with GPIB driver in my coding and tried to send the
data to the Digital Multimeter, Whenever i send the data, it throws this Exception
" System.AccessViolationException: Attempted to read or write protected memory. This is often an
indication that other memory is corrupt." , but i will send the data from VC++ application,its
working fine. Is there any specific settings needs to do Please help me to solve this problem.
For your reference i have pasted the header file function ,VC++ coding as well as C# coding here.
Header file function
----------------------------
extern long int _cdecl ieee488_send (long int,char *,unsigned long,long int *);
#define send(addr,s,status) ieee488_send(addr,(char *) (s),0xFFFF,(long int *) status)
VC++
----------
send(temp,info,&status);
info is character pointer
Status - int
C# -- I have tried in the folowing ways
------------------------------------------------------
1. [DllImport("IIEEE_32M")]
public extern static int send(int address,string strCommand , ref int status);
send(inGpibAddress, Command, ref inStatus);
2. [DllImport("IIEEE_32M")]
public extern static int send(int address,string strCommand , out int status);
send(inGpibAddress, Command, out inStatus);
3. [DllImport("IIEEE_32M")]
public extern static int send(int address,[MarshalAs(UnmanagedType.LPStr)] string
strCommand, out int status);
send(inGpibAddress, Command, out inStatus);
4. [DllImport("IIEEE_32M")]
public extern static int send(int address,[MarshalAs(UnmanagedType.LPStr)] string
strCommand, intptr status);
send(inGpibAddress, Command, out intptr inStatus);
Thanks in advance
invoking native dlls in c#
GiannaCampbell
First if you are using a national instruments card, they have a .Net driver on their web site, it saves a ton of time.
Otherwise you have to "decorate" everything (real important as long has changed length twice!), change strings to char[] and often change pointers (most old strings are just pointers) to ref.
Example
[
DllImport("My.DLL")] [return: MarshalAs(UnmanagedType.U4)] private static extern unsafe uint MyMessage([
MarshalAs(UnmanagedType.U4)]uint configval,[
MarshalAs(UnmanagedType.U2)]ushort cwd1,[
MarshalAs(UnmanagedType.U2)]ushort cwd2,[
MarshalAs(UnmanagedType.LPArray)]ref ushort[] data,[
MarshalAs(UnmanagedType.I4)]int handleval);