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Hi guys,
I need to save data from my program at certain intervals (in case my program gets terminated/evicted).
In order for the data to be saved... must the file be closed?
Is there an efficient way to do this or just what I am thinking:
At given intervals:
-Check if temp file is open... open the file
-write data to file
-close the file
- ... wait for next interval
Any ideas/helps?
Many thanks
If the data has a fairly structured format and the file size does not arbitrarily change ((what happens is the newer file is smaller in size than the older?)) , you can seek to ios::beg and dump the entire contents at the intervals.
To be more sophisticated, you have to keep track of all changes during the intervals and seek to the necessary stream positions to update.
Thanks manasij I'll bear that in mind.
The other thing is:
I will be saving 3 data files. Each one contains crucial information for re-starting the program from the last save point (incase it gets cut off).
I need either all of them to save or none of them (at each interval). I am thinking now of the specific case when the program is closed down inbetween saves of any of these 3 files.
To try to avoid this I am doing this:
This will minimise the chance of the program closing out inbetween these file saves but it not guaranteed.Code:file_A.close(); file_B.close(); file_C.close();
Is there anyway to guarantee this without having to save all this info in the same file (as it is much more convenient to have 3 separate files)?
Many thanks
It seems like you cannot even guarantee that the writing to the one file will not be cut off in the middle of the process. I suggest you use a folder for each interval so you don't damage previously written files.
Like nvoigt says, if you are trying to protect against any and every possible cause (eg, the power being turned off), there is no way to guarantee three files can be left in a parallel state, so you would have to use three series of multiple snapshots with some kind of indicator at the end showing:
a) the write was complete
b) at which stage this write occurred, corroborated to files in the other two series.
Then at start-up you'd have a routine to assess the three series and select the last three complete parallel records.
However, if there is a more specific reason for the program "getting cut-off" and you expain that and what OS you're on, there may be simpler options.
Quote:
I suggest you use a folder for each interval so you don't damage previously written files.
Can't only diffs be stored w.r.t some base data, that would not change much ?Quote:
there may be simpler options.
You could, but you must still save them in different files in order to be sure.
Have you considered a transactional database?
Database transaction - Wikipedia, the free encyclopedia
They've solved all the "did it, didn't it, is it consistent' problems.
Some great comments. Thanks guys.