-The above example will produce a Runtime Error (see below):

Runtime error
/Users/paulh/Desktop/system.pathForFile/main.lua:7: bad argument #1 to 'close' (FILE* expected, got nil)
stack traceback:
[C]: ?
[C]: in function 'close'
/Users/paulh/Desktop/system.pathForFile/main.lua:7: in main chunk
Runtime error: /Users/paulh/Desktop/system.pathForFile/main.lua:7: bad argument #1 to 'close' (FILE* expected, got nil)
stack traceback:
[C]: ?
[C]: in function 'close'
/Users/paulh/Desktop/system.pathForFile/main.lua:7: in main chunk

-Solution

Replace fhd.close() with io.close( fhd ) (see code below)

1
2
3
4
5
6
7
8
9
10
11

local path = system.pathForFile(  "data.txt", system.DocumentsDirectory )
local fhd = io.open( path )
 
-- Determine if file exists
if fhd then
   print( "File exists" )
   --fhd.close() <- Produces a Runtime Error. Use io.close( fhd )
   io.close( fhd )
else
    print( "File does not exist!" )
end

Sincerely,

Paul Allan Harrington
http://www.pahgroup.com

Shouldn't you check for path too? Because if I don't I get a Runtime error from the open function if the string given to system.pathForFile doesn't map to an actual file.

Runtime error
... bad argument #1 to 'open' (string expected, got nil)

1
2
3
4
5
6
7
8
9
10
11
12

local path = system.pathForFile( "data.txt", system.ResourceDirectory )
if path then -- file exists
        local file = io.open( path, "r" )
 
        if file then -- nil if no file found
                local contents = file:read( "*a" )
                print( "Contents of " .. path .. "\n" .. contents )
                io.close( file )
        end
else
        print( 'file does not exist' )
end

While checking for nil might seem useless because "you should know whether the file is there" it comes in handy for me during development. I have a button routine that puts up a button and shows a depressed version when pressed...

...except when I'm developing and haven't done the depressed version yet, it will still work with just the one button...

...and even before that if there's NO button artwork yet it will display a text object that acts like a button.

Which means I can use the same button code from day 1 to the day I ship and never have to change anything except throw the button artwork in whenever I get it. :)

Just one example of how this can be used.

Jay