sharing a refnum between case structures

[jbolin]

I would like to output some data to a file with a custom header and data format.  I have created a simple true/false case structure within a while loop where the data is aquired.  If the while loop count is 0, I would like to output a custom header to a file using the "Write to a Text File Function".  For this fuction I planned on leaving the file name blank so it will prompt the user with a file dialog.  If not on the first iteration of the while loop I would like to send my data to the same file with the header using the "Write to Text File Function" again.  I would like to use the output refnum from the "Write to Text File Function" and use it as input for the second function that writes the data.  Any ideas?  I am unsure how to share the refnum between the case structures so there is only one file dialog shown to the user.  I have attached a sample vi.

[nathand]

You should store the file refnum in a shift register (right-click the border of the while loop, add shift register).

[crossrulz]

Just for a good reference, you should do some research on the State Machine architecture.  I can't find my normal page now (on a different computer than normal right now), but here's a good example I found really quick.

https://decibel.ni.com/content/groups/northeast-oh-labview-users/blog/2009/09/08/state-machines

[Turzt]

Hello!

A bit old thread but I'd like just a clarification for file refnums as well:

I have a state machine structure (basicly a case structure with different file operations in each case).

I open file in one case, and pass in into feedback loop outside the case structure and input it back to the case structure.

Is it so that because I exit the case structure, the file refnum becomes invalid? Or should it stay persistent until I explicitly use close file VI?

I am experiencing an error code = 1 when trying to close a file that I opened in other case.

If so, what are my options to preserve a valid file I/O refnum? shift register? global variable? local variable? some other?

I feel that my files are getting closed without any warning!

[dkfire]

How are you runing your vi? With Run button?

Doesn't your vi have a while loop?

[nyc_(is_out_of_here)]

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@Turzt wrote:

Hello!

A bit old thread but I'd like just a clarification for file refnums as well:

I have a state machine structure (basicly a case structure with different file operations in each case).

I open file in one case, and pass in into feedback loop outside the case structure and input it back to the case structure.

Is it so that because I exit the case structure, the file refnum becomes invalid? Or should it stay persistent until I explicitly use close file VI?

I am experiencing an error code = 1 when trying to close a file that I opened in other case.

If so, what are my options to preserve a valid file I/O refnum? shift register? global variable? local variable? some other?

I feel that my files are getting closed without any warning!

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No VI hard to answer.

[crossrulz]

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@Turzt wrote:

I have a state machine structure (basicly a case structure with different file operations in each case).

I open file in one case, and pass in into feedback loop outside the case structure and input it back to the case structure.

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Why are you using a Feedback Node in a State Machine?  Why not just use the shift register?  In this case, that would make things a little cleaner.

My guess to your problem is that you are not passing the reference through all of your cases.  But without code, it is impossible to actually debug.

[Turzt]

The reason for using feedback node for state machine state and other variables is that the state machine is in a subVI which is inside a main VI.

If I put neverending while loop into subVI, the subVI never exits and the main VI gets stuck waiting the subVI.

I made a test and put while loop and shift register outside the state machine. Now it works. So, I must not ever exit the structure that contains the "open file" VI.

So I guess I must open the file in the main level and just pass requests from the state machine subVI. I don't want to create file immediately at start, but I need

to wait user command to create file and start logging data into file, and then other user command to stop logging and close the file.

[Queue-tip]

Could you please clarify your question?