Hello KB,
it seems you are trying to write a LabView program by
inserting C-code into a formula node... That's not the way it should be.
As far as I know there is no way to open a file inside the formula node. (It's a "formula" node!) So you have to open the file with LabView for reading and/or writing. Use your prefered subVi from the file palette. Perhaps you have to convert the data to a format suitable for your formula node (like string to U8-array).
In my experience it's better to use Labview-code instead of the formula node. In my programs a formula node was always slower than Labview code. So you should think about converting the C-style code to Labview.
Best regards,
GerdW
Best regards,
GerdW
using LV2016/2019/2021 on Win10/11+cRIO, TestStand2016/2019