Create a header in an SD card file

[Joe Tauser]

Is there a way to tell if a file exists on an SD card before calling Write Delimited line?  I want to write a header in the first line before I start filling a file with data that someone may or may not recognize.

In the past I've manually triggered a Write Line that had the header text, but this seems hokey.

Joe T. 

[Ausman]

If I'm understanding the question correctly, could you use bit 2 in Status Messages MI of SD File Info to answer the question in a round about way?  If it can't read it, then it isn't there?

cheers,

Aus

[Joe Tauser]

I'll give that a try and report.

Joe T.

[Joe Tauser]

Empirically confirmed that bit 2 of the status word does not come on if the file doesn't exist.  If everything else is OK on the SD it just goes ahead and creates the file and writes the line.

Joe T.

[Joe Tauser]

Also, I opened the file in Notepad++ and my data string is in the middle of a huge number of NUL characters.  What's up with that?

Creators?

Joe T.

[Ausman]

So it worked out mostly ok?  In reading the help file my interpretation was that Bit 2 would be ON if the file wasn't found.  Just confirming that you're finding that it is OFF with no file name match, and ON with file present?

Maybe the nulls are some sort of maximum?  256 characters in total?

I haven't time to play with this at present, but am curious about it for future reference.

cheers,

Aus

[Joe Tauser]

Talked to Dan at US tech support - he suggested SD File Utilities -> File Status function block

The "A" output bit MB 39 does what I need.  I just call this function before I write the data line to see if I have to call a another Write Line for the header first.

Joe T.