Weird problem with 'for' and 'io.open'

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Moshroom

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Posted: 26th Oct 2015 12:55

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Hi. I'm trying to create a graphical interface for my save/load script and I encountered pretty weird error with the following code:

+ Code Snippet

  for i = 1,NUM_SLOTS do
   local file = io.open("slot" .. i .. ".dat", "r")
   if file == nil then
   	Text(30,20 + (i - 1) * 10,TextSize,"[empty slot]")
   else
    Text(30,20 + (i - 1) * 10,TextSize,"Slot " .. i)
   end
  end

The purpose of this code is to draw a list of saved games. I there is no saved game, file returns nil and the program writes "empty slot". If the save exist, the program writes the number of the slot (this way just for a proof of principle. Later I'm going to add some details about the saved game to the list).

But my problem is that occasionally (about once every 10 seconds) the used slots change to "empty slot" for a second and then turn back to SlotX. Also the code takes a LOT of memory to run. My guess is that either GameGuru somehow wastes memory when handling 'for' statement (kind of explains why almost all of the default scripts use merely if-else statements), or (which I feel is more likely) that io.open("slot" .. i .. ".dat", "r") eats unneccessarily lot of memory. Has somebody else encountered this before? Does an io command exist to just check whether a file exists without opening it?

(I know that this can be worked around by reading all the dats once, storing their data to unique local variables and building the list using if-else statements, but this takes almost 30 lines of pretty non-elegant and self-repeating code. I post this here because I'd like to know whether there is any better way to do it.)

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Bored of the Rings

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Posted: 26th Oct 2015 13:14

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Where are you placing the code within the function?

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Moshroom

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Posted: 26th Oct 2015 15:25

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Well, the script is far from finished, but here's the context so far. ActiveMenu is set as 6 when player calls save menu (I haven't yet decided how player should do this. Probably from main menu or by pressing E near save point):

+ Code Snippet

if ActiveMenu == 6 then
  -- Initiate the active command
  NumCommands[ActiveMenu] = NUM_SLOTS
  Command(e)
  
  -- Top panel text
  TextCenterOnX(50,5,TextSize,"Save Game")
  
  -- Draw the main panel
  Panel(25,10,100,90)
  
  -- Draw cursor
  Panel(28,15 + 10 * (ActiveCommand[ActiveMenu] - 1),97,25 + 10 * (ActiveCommand[ActiveMenu] - 1))
  
  for i = 1,NUM_SLOTS do
   local file = io.open("slot" .. i .. ".dat", "r")
   if file == nil then
   	Text(30,20 + (i - 1) * 10,TextSize,"[empty slot]")
   else
    Text(30,20 + (i - 1) * 10,TextSize,"Slot " .. i)
   end
  end
  
  -- Exit menu by pressing Q button
  if g_InKey == "q" and GetTimer(e) > BtnTime[e] or g_InKey == "Q" and GetTimer(e)>BtnTime[e] then
   BtnTime[e] = GetTimer(e) + 500
   ActiveMenu = 1
  end
 end

The cursor is controlled by Command() which is introduced as a separate function before main().

+ Code Snippet

function Command(e)
 -- Initiate the command
 if ActiveCommand[ActiveMenu] == nil then
  ActiveCommand[ActiveMenu] = 1
 end
 -- Update menu when player presses up/down
 if g_InKey == "w" and GetTimer(e) > BtnTime[e] or g_InKey == "W" and GetTimer(e) > BtnTime[e] then
  BtnTime[e] = GetTimer(e) + TIME_W
  ActiveCommand[ActiveMenu] = ActiveCommand[ActiveMenu] - 1
 end
 if g_InKey == "s" and GetTimer(e) > BtnTime[e] or g_InKey == "S" and GetTimer(e) > BtnTime[e] then
  BtnTime[e] = GetTimer(e) + TIME_W
  ActiveCommand[ActiveMenu] = ActiveCommand[ActiveMenu] + 1
 end 
 -- Set limits for the command - Wrap
 if ActiveCommand[ActiveMenu] > NumCommands[ActiveMenu] then
  ActiveCommand[ActiveMenu] = 1
 end
 if ActiveCommand[ActiveMenu] < 1 then
  ActiveCommand[ActiveMenu] = NumCommands[ActiveMenu]
 end
end

NUM_SLOTS is 7 and TIME_W is 145. I don't think Command() is causing problems because other menus using it are working just fine. "Top panel" is introduced if any of my menus is active (I'm planning to create various menus that work with the same logic, for example inventory and shop.)

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smallg

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Posted: 26th Oct 2015 16:20

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+ Code Snippet

TextCenterOnX(50,5,TextSize,"Save Game")
   
  -- Draw the main panel
  Panel(25,10,100,90)
   
  -- Draw cursor
  --Panel(28,15 + 10 * (ActiveCommand[ActiveMenu] - 1),97,25 + 10 * (ActiveCommand[ActiveMenu] - 1))
  
   local i = 0
 while i < NUM_SLOTS do
 i = i + 1 
   local file = io.open("slot" .. i .. ".dat", "r")
   if file == nil then
    Text(30,20 + (i - 1) * 10,TextSize,"[empty slot]")
   else
    Text(30,20 + (i - 1) * 10,TextSize,"Slot " .. i)
	io.close(file)
   end
  
  end

life\'s one big game

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i5 @3.3ghz, 4gb ram, AMD R9 200 series , directx 11

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Moshroom

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Posted: 26th Oct 2015 17:56 Edited at: 26th Oct 2015 18:06

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Quote: "io.close(file)"

HAHAHA! I feel like an idiot now. Thanks. Sometimes the most obivious thing is the most difficult to notice.

By the way in this case 'for' and 'while' statements have at least superficially similar effects. Is there some (for example memory or performace related) reason to use 'while' instead of 'for' that I'm not aware of?

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smallg

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Posted: 26th Oct 2015 18:46

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'for' is generally better and easier to use in lua/GG from my experience (much less likely to cause system lock up too), i just used 'while' as an alternative while i was testing and added the 'close' later when it still didnt work.

life\'s one big game

windows vista ultimate

i5 @3.3ghz, 4gb ram, AMD R9 200 series , directx 11

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3com

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Posted: 27th Oct 2015 17:15

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Quote: "Does an io command exist to just check whether a file exists without opening it?"

This function might help:

+ Code Snippet

-- Return true if file exists and is readable.
function file_exists(path)
  local file = io.open(path, "rb")
  if file then file:close() end
  return file ~= nil
end

hth

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