Display value of a structure or member variable

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Guest

I have a class library project that uses unmanaged C dll to perform some
image handling. This DLL requires me to pass in a structure containing image
coordinates. In VB6, I could use a type/endtype and define left, top, right,
and bottom coordinates. In .NET, I can use a structure to do the same thing.

In .NET only, I have found odd behavior in my C DLL, so in debugging, I try
to view the values of my 4 public variables in my structure. I do this
BEFORE I pass the structure to the C DLL. The values of the member variables
are not the values I assigned them. In fact, I execute a line like this:

struct.top = intVariable

then, after executing this line, I try to display the value of this
variable. All member variables behave the same - they all evaluate to zero.

If I attempt to execute this same line in the debugger, I get a debugger
error:

System Error &H80131303&

If I write a test application (standalong EXE), I do not see this behavior.

Is there anything I can do to find out if my C dll is getting nothing but
"0" ?

Is there something about the system error that's causing this problem?

In researching this system error, I found it's about a core class that's not
loaded, although it doesn't say what class. My class library is being loaded
late-bound, and I'm using reflection to load the DLL into memory. Is this
related?

thanks,
andrew
 
Can you post relevant parts of your code (like the native structure
definition and your corresponding VB version)?


Mattias
 
Hi,

Sorry for the delay...

This is the structure:
Public Structure RTKRECT
Public left As Short
Public top As Short
Public right As Short
Public bottom As Short
End Structure


this is the intialization:
MyFunct(
ByVal lAbsLeft As UInt16, _
ByVal lAbsTop As UInt16, _
ByVal lAbsRight As UInt16, _
ByVal lAbsBottom As UInt16, _
....)

Dim rectCrop As New RTKRECT

And this is how I set up the variables:

'TODO: fix when setting these values when at coordinates
1100,0,1300,100 causes all to be "0"
rectCrop.left = lAbsLeft
rectCrop.top = lAbsTop
rectCrop.right = lAbsRight
rectCrop.bottom = lAbsBottom


I have additional information I didn't have before:

When the structure is defined such that the member variables are of type
"Short" then there is no problem to report - everything works as expected,
even if the local variables are uint16, int16, ushort, or short.

when I declare the structure's member variables as either "UShort" or
"Int16" or "UInt16" then I see the problem. It seems that the UInt and Int16
are not fully CLR-compliant data types, which might explain the behavior.
However, UShort is CLR-compliant, and therefore does not explain the behavior.

FYI - I am lucky in that the rect structure (image coordinates) can be
passed to a C-library when I use SHORT as long as my coordinates do not
exceed 32767, even though the library expects unsigned data types.

I suspect that other people who need to provide data outside this range must
pass in negative numbers to get to the range +32768 to +65535?

It makes no difference if I use the "New" keyword for initializing the
structure.

I cannot reproduce the problem in any combination of conditions if I test
inside a standalone windows application, but in my application, the code
resides in a class library who is loaded late-bound using reflection. Not
sure if this is relevant, but might explain behavior between standalone exe
and dll.

aj
 
When the structure is defined such that the member variables are of type
"Short" then there is no problem to report - everything works as expected,
even if the local variables are uint16, int16, ushort, or short.

when I declare the structure's member variables as either "UShort" or
"Int16" or "UInt16" then I see the problem. It seems that the UInt and Int16
are not fully CLR-compliant data types, which might explain the behavior.
However, UShort is CLR-compliant, and therefore does not explain the behavior.
Click to expand...

Well your problem sounds more and more strange. Short and Int16 are
the exact same types (Short is just a VB alias keyword for Int16), so
there should be no difference whatsoever in behavior.

But unless you can post a short sample application that will let us
reproduce the problem, I don't think I can be of much help.


Mattias
 
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