Precautions to avoid savegame corruption?

One problem I have had from user in my latest game is that saved games sometimes corrupt or disappear, especially on the mobile versions of the game. This of course cause great frustrations of the user, especially if they have bought ingame inapps like gems etc. It is thankfully not common, but I have still had a bunch of one stars from people this have happened to. One of the "problems" with my game I guess is that the game is always "on" (there is no level complete screen etc) so saving happens in even intervals. I guess this makes it so the user could quit the game in the middle of a save, or like I have heard also having it crash on them just in the middle of a save. I am using an ini to save to.

Now, my question is if there are ways to minimize this and prevent data loss in this way?

The way I do this (which I'm sure is grossly inefficient, but, it works) is:
Write all counter contents (or whatever format variables are saved as) to the .ini. Have a second set of (identical) variables reserved for checking. Only allow exit once a group that does the following has completed:

1. Pulls all variables out of the ini (and into the second set of variables)
2. Compare each variable that "variable from set 1" = [it's mirrored counterpart from] "variable from set 2".
3. If they *all* match, allow exit.
4. If there's a discrepancy, repeat the process of writing "set 1" variable to the ini and restart this group.

If people actually force the app to shut (EG 'terminating the process' or pulling the battery out mid-game), they're stupid to expect it to save and deserve corrupt data. ;)

Some other ideas:

Keep two save files,
save at different time intervals,
add a control line as last operation to validate the save file
and only load the "uncorrupted" (validated) save file on game restart

This could limit the problem I guess?

If you were not saving all time,
you could have added a "progress bar" also,
once saving is complete
(test for last control line written)
print out something like "save ok - safe to quit"
but people like to mess anyway XD

Thanks for the tips!

About this one though: add a control line as last operation to validate the save file
and only load the "uncorrupted" (validated) save file on game restart

How would this look like in practice to check if it is not corrupted?

*I think*
(never actually did something like that, so it's just theory >:))
you can write your savedata as you already do,
i.e.

Lives = 5
Score = 1000
(...)

And then, as last operation when saving data,
add something like this:

Control_line = 1234

Then on loading,
if you don't find the "control line",
it means the file has been corrupted
(since writing to ini would have been stopped before that last line being added)

and then you would check the other save file for the same control line, hoping that is not corrupted
(which would be highly unlikely, because one can't quit the application at the same time one second after and one second before XD)

Yep, I've done it previously with a .ini, where the last thing it does is write a aboveAreAllValid=1 line. Then future frames/restarted games that need to reference it can check that it's in place and write a warning saying "possible ini file corruption" when it's missing.

Technically of course, the values above it could be corrupted. In practice, I've yet to have it fail though and have written this ini file hundreds of times on a dozen phones.

Thanks for the input about this! :) I have read though that using arrays is better for saving since it is not as easy for the user to just edit the ini file. I might go over to using an array in my next project. Would this method also work with an array file?

Btw, how would one go about to alternate saving to the two different ini files? Could I do it in an event, or would I need to do double the amount of save conditions depending on what ini to save to? (would suck :/ )

Also if you are going to do this thing I assume you need to save every single data every time you save? You can't just update the save with the player losing a life for example, since then it will only update in one of the files and if you then save another data to the other file it will not have been updated with the player losing a life in the previous file etc.

Call me obsessed with arrays, but if your system used arrays instead of INI, you could run a nested loop through the main array and simply have the other array copy each index. So you effectively have a "copy" function. Might also make checking for corruption easier, since you can move through cells the same way and compare.

"I guess this makes it so the user could quit the game in the middle of a save, or like I have heard also having it crash on them just in the middle of a save."

Have you actually checked that this does/ can corrupt the savegame, on your end i mean?
Just so your not missplacing your efforts to solve the problem

+1 for arrays
(much, much) faster, more flexible, more handy for multiple savefiles, harder to break (but not that much actually..)

Quote:

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Originally Posted by Outcast

Btw, how would one go about to alternate saving to the two different ini files? Could I do it in an event, or would I need to do double the amount of save conditions depending on what ini to save to? (would suck :/ )

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You just need to prepare your "routine" once, and then, since you can dynamically feed your INI file savenames,
just trigger that routine twice, feeding once "savefile1.ini", and then "savefile2.ini" as filenames

Quote:

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Also if you are going to do this thing I assume you need to save every single data every time you save? You can't just update the save with the player losing a life for example, since then it will only update in one of the files and if you then save another data to the other file it will not have been updated with the player losing a life in the previous file etc.

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Each time you want to access the savefile,
even for single addition/changes
you can do this:

1) open access (set control_value to 0)
2) do your stuff
3) close access (set control_value to 1)

if you'll find control_value=0, will mean that your file is unfortuntely corrupted!

So the full method would be:

1) set file "savefile1"
2) open access (set control_value to 0)
3) do your stuff
4) close access (set control_value to 1)
5) set file "savefile2"
6) trigger above points 2,3,4

And on loading:

1) open file "savefile1"
2) check control_value
3) control_value=0 >> open file "savefile2", check control_value
4) control_value=1 >> load game

Quote:

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Originally Posted by casleziro

Call me obsessed with arrays, but if your system used arrays instead of INI, you could run a nested loop through the main array and simply have the other array copy each index. So you effectively have a "copy" function. Might also make checking for corruption easier, since you can move through cells the same way and compare.

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For sure. Presumably, you could even (if you're not using all 3 dimensions already) use an unused dimension in one array for the 'mirrored variables' and even do it with one logical array. :)

King_Cool: The most common thing I hear is (My game crashed (or battery ran out) and when I opened it again all my progress was lost and I had to start from the beginning, **** this game etc :p) So I assume what most often happens is that the game crashes in the middle of saving and that corrupts the save file.

I assume the best way to handle something like that is to save a set number of backups in a buffer over a certain amount of time. Something like 3-5 backups, and you add a new one every so many minutes, deleting the oldest one from the buffer. This way if the app crashes you still have the older backups to default to. They might lose a bit of progress but at least they didn't lose all of it.

I agree with Casleziro.
Without delving into anything specific, i think the main key to solving this it to be able to assess if corruption has taken place or not.
If you with certainty can asess if curruption has taken place, you can just deliver a message to User and revert to the previous backup/ save file.

Dont have much experience with this, but isjust my logical way of thinking.