Persistent Data

PB____

I've noticed that you don't declare your function scoped variables.

It is likely that someone uses a variable called i in their for loop. If they do this in the global scope and use getValue within that for loop, the i value of the global varible i would be changed by getValue. This could be fixed as follows:

// Get the value for the specified key
function getValue( key )
    var i = 0
    var result = "Undefined"
    var found = false
    while i < len(store) and !found loop
        if store[i].key == key then
            found = true
            result = store[i].value
        else
            i += 1
        endif
    repeat
    if found then
        if store[i].type == "int" then
            result = int( result )
        endif
        if store[i].type == "str" then
            result = str( result )
        endif
        if store[i].type == "float" then
            result = float( result )
        endif
    endif
return result

I now var is not a keyword (you could use int in stead), it's a personal preference, mainly since boolean found = false doesn't appear to be technically correct either.

LinkCraft

Wait I’m confused is this so you can access data from any program

PB____

@LinkCraft02 I think you might have misread "a way of persisting data across programs" in stead of " a way of persisting data across program runs" ?

I think you can only access the file that belongs to project you are running.

pianofire

I have updated this in line with the @PB____ recommendations.

Also it now supports vector types

password1

@pianofire please post a usage example.

pianofire

There are some examples in the download:

// Initialize values or load from the store
if !loadStore() then // init on first run
    setValue( "test1", 99, "int" )
    setValue( "test2", "", "str" )
    setValue( "test3", pi, "float" )
    setValue( "test4", { 0, 1, 2, 3 }, "vector" )
endif

// Get values from store
test1 = getValue( "test1" )
test2 = getValue( "test2" )
test3 = getValue( "test3" )
test4 = getValue( "test4" )

// Show current values
finished = false
while !finished loop
    clear()
    c = controls( 0 )
    printAt( 0, 0, "Press X to exit" )
    printAt( 0, 1, "test1 : ", test1 )
    printAt( 0, 2, "test2 : ", test2 )
    printAt( 0, 3, "test3 : ", test3 )
    printAt( 0, 4, "test4 : ", test4 )
    finished = c.x
    update()
repeat

// Change values
test1 = test1 + 1
test2 = test2 + "wibble"
test3 = test3 * 2
test4 = { test4.x + 1, test4.y * 2, test4.z - 1, test4.w / 2 }

// Save current values to store
setValue( "test1", test1, "int" )
setValue( "test2", test2, "str"  )
setValue( "test3", test3, "float" )
setValue( "test4", test4, "vector" )

saveStore() // save store to file

PB____

@pianofire I can't seem to download from the code NDZQHDNDNN anymore.
I did evolve the code to my preferences anyway (since you're in my friends-list, you could check it out on NDSF6DND1Z, it's part of my template project that I intend to use for my new projects)

pianofire

@PB____ Sorry my fault I unshared it so the code changed. The new code is FPH33MNDNN

I have had a quick look at what you have done and it looks very impressive. That looks like an incredible amount of work! I will update my example using your code if that is OK (with credit of course)

PB____

@pianofire Thanks :-) I hope the work pays off. Since it's my template project, I hope that the work I put in it, will benefit all my future projects, so as a net result, it saves me work overall :)
And of course I'm OK with it if you can improve the file storage example based on my code :-). I'd like to clarify my thought process about how I start the file:

// file format (to enable compatibility check)
file_writeLine(file, "PB")
// reserved for updates to the file format:
file_writeLine(file, 0)

Currently projects can only have one file, and it's not possible to share files across different projects. But still I thought it was a good idea to mark a file format at the start of the file, just in case the mentioned limitations change in the future. Of course this means that I hope that other people won't mark their files with the same opening as I did, to prevent potential errors in the future :-)

The second line (0) is to mark a version of the format. In case people download an updated version of a program, and I need to check how to handle the format of an older file (in case the download mechanism doesn't include saved files in the future, since it has been suggested that that behavior is a bug).

waldron

could this be simplified to save a sprites location using maps

pianofire

@waldron I am not sure what you mean. It can already save vectors (such as a sprite position). There is one in the example above

waldron

@pianofire of course, il wait till i'm off to have a proper look

PickleCatStars

@pianofire said in Persistent Data:

@PB____ Sorry my fault I unshared it so the code changed. The new code is FPH33MNDNN

I have had a quick look at what you have done and it looks very impressive. That looks like an incredible amount of work! I will update my example using your code if that is OK (with credit of course)

Project not found! :/

pianofire

Sorry I accidentally unshared some stuff the new code is: XP6L3MNDNN

PickleCatStars

Thankyou very much :)

pianofire

I have been asked to give some more information about how to use this and how it works so first how to use it:

Download the program (XP6L3MNDNN)
Copy the functions into your program (Line 60 onwards)
In your global variables declare

store = []

Initialise any variables that you want to save e.g.

// Initialize values or load from the store
if !loadStore() then // init on first run
    setValue( "test1", 99, "int" )
    setValue( "test2", "", "str" )
    setValue( "test3", pi, "float" )
    setValue( "test4", { 0, 1, 2, 3 }, "vector" )
endif

Read the current values from the store e.g.

// Get values from store
test1 = getValue( "test1" )
test2 = getValue( "test2" )
test3 = getValue( "test3" )
test4 = getValue( "test4" )

When you want to save the current values to a file (or just at the end of your program)

Set the current values in the store:

// Save current values to store
setValue( "test1", test1, "int" )
setValue( "test2", test2, "str"  )
setValue( "test3", test3, "float" )
setValue( "test4", test4, "vector" )

Save the store to a file:

saveStore() // save store to file

And that's it!

pianofire

OK so now how it works:

store is a list of structs with a key, value and type. This is a sort of dictionary in that the key is unique and can be used to retrieve the value. It only does a sequential search so will get quite slow if there are a lot of entries.

The type is needed because the store actually keeps everything as strings and converts to and from the actual data type.

Persistent Data.png

So store acts as a backing store which mirrors the types and values of variables that you want to persist. There are load and save store methods that either save the current state of these values or restore a previously saved state.

The values are then stored in the file as variable length text records something like this:

4   5   test13   int3   1005   test23   str6   wibble5   test35   float8   6.2831865   test46   vector42  { 1.000000, 2.000000, 1.000000, 1.500000 }

The first number is the number of entries in the file. Then the next one is the length of the variable name. Next the name itself, then the length of the type, the type, length of the value, the value and so on.

The clearStore method empties the backing store and saves the empty store to the file.

SteveZX81

Well, I don't know about anyone else but this helped me a ton and now I actually understand it and have added a saved high score to my game.
Thank you so much!

nintisonfire

Thanks for this. Got a high score that saves. Forgive my ignorance. Are "setValue" and "getValue" new inbuilt functions? They don't turn change colour when typed into the code editor.

PB____

To use this, you need to copy Pianofires code into your project (I think it's game id XP6L3MNDNN, or it might be FPH33MNDNN as mentioned in the initial post).