Hi,
I am having problems with the following operation to call GetConnectionInfo in VC++ 6 from c# 2.0
C++ Constructs as follows:
typedef
struct _OUTPUTPOINT {BYTE cDevicePath[MAX_PATH +8];
//DevicePathBYTE cLinkPath[1024];
//Use Lib.} OUTPUTPOINT, *POUTPUTPOINT;
typedef
DWORD ( CALLBACK *pfnGetConnectionInfo )( POUTPUTPOINT );
C# Constructs:
[
StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)] public class OutPutPoint{
public char[] cDevicePath; public char[] cLinkPath;}
IntPtr outArray; uint retVal = GetConnInfo(out outArray); OutPutPoint output = new OutPutPoint(); Marshal.PtrToStructure(outArray, output); MessageBox.Show(outArray.ToString());Just want to get the POUTPOINT struct[] to come back with info that I can use, I am a beginner at Interop and p/invoke operations and any help would be hugely appreciated
Thanks in advance.
Problem with Interop DllImport Memory Corruption and AccessViolationException
Monish Nagisetty
Neil Tippett
I now get a 'FatalExecutionEngineError exception
Code as follows:
[
StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)] public class OutPutPoint{
[
MarshalAs(UnmanagedType.ByValArray, SizeConst=264)] public char[] cDevicePath;[
MarshalAs(UnmanagedType.ByValArray, SizeConst=1024)] public char[] cLinkPath;}
[
DllImport("CTRL150.DLL", CallingConvention = CallingConvention.Winapi,EntryPoint =
"GetConnectionInfo")] public static extern uint GetConnectionInfo(out IntPtr outArray);
uint retVal = GetConnectionInfo(out outArray); MessageBox.Show(outArray.ToString());Deerhake44
You've almost got it. Remember that in C++ an array is just a pointer so in your case you are marshalling two pointers to C++ but it is expecting buffers. Therefore you need to modify your C# structure definition to define the size of the arrays (MAX_PATH+8 and 1024) respectively. One way to do this is use the MarshalAs attribute and specify the SizeConst option to specify the length:
[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
public class OutPutPoint
{
[MarshalAs(UnmanagedType.ByValArray, SizeConst=264)]
public char[] cDevicePath;
[MarshalAs(UnmanagedType.ByValArray, SizeConst=1024)]
public char[] cLinkPath;
}
Michael Taylor - 12/8/06
PaulSw
Got that too work by changing removing out from extern call
I assume its because its a class so marshalled byref by default
Now getting wierd characters at the start of cLinkPath does anyone have any suggestions
Thanks in advance
Biggo
I've now got a System.AccessViolationException with the following code
[
StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)] public class OutPutPoint{
[MarshalAs(UnmanagedType.ByValArray, SizeConst = 264)] public char[] cDevicePath;[
MarshalAs(UnmanagedType.ByValArray, SizeConst = 1024)] public char[] cLinkPath;}
public class PrinterManager{
public OutPutPoint[] appOutputPoints;[
DllImport("CTRL150.DLL", CallingConvention = CallingConvention.StdCall,EntryPoint =
"GetConnectionInfo", ExactSpelling = false)] public static extern uint wGetConnectionInfo(out IntPtr outArray); public void GetConnectionInfo(){
IntPtr outArray; uint retVal = wGetConnectionInfo(out outArray);}
}