Weird memory corruption when assigning a POINT array

[richferrara1]

Trying to use Windows GDI functions to draw a simple shape on the screen, as my application does in many other functions. This time I'm seeing an inexplicable memory error. See the attached code.

[Sporty]

I've never used the windoze drawing tools, but I have encountered stuff like what you are seeing occasionally.

It may seem silly, but I'd try rearranging the order in which you perform some of your operations... as simple as declaring the variables in a different order, and setting up your points array values before you set up the pen.  It could be that your oldPen variable is declared based on an older return data size, and you've got a newer .dll that returns a larger amount of data from the SelectObject function than expected... and subsequently overwrites some of your point array. Try switching the order up and see if you see any difference in where the memory is getting corrupted.

[rolfk]

There's also the option that the C compiler is actually messing up the stack somehow. I've seen reports before where CVI seemed to have trouble with arrays declared on the stack and not quite reserving the right amount of stack space for it. You might try to use a dynamically allocated array and afterwards deallocate it. Yes it's not nice and feels rather awkward in terms of simplicity and performance, but sometimes you have to row with the paddles you have, rather than hoping to get better ones.

Also interesting would be to know the CVI version. My memory, which never has been faultless, seems to say that this was an issue with CVI 2017 or maybe 2019, but I'm not sure.

[richferrara1]

It's version 2013.

[rolfk]

What are your possibilities to try with a newer version? The problem definitely sounds remotely familiar and it was related to certain CVI versions. But my memory isn't anymore what it never was to start with, so which specific version this was occuring with is shrouded in mystery.