BBC BASIC for Windows
Programming >> Database and Files >> BB4W can't open file with no extension!
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BB4W can't open file with no extension!
Post by Endymion on May 15th, 2012, 06:37am

Code:
      FILE$ = "SCH_LIST"
      File1% = openin(FILE$)
      if not File1% then end
...other parts of the program....


This program doesn't work. Renaming file to "SCH_LIST.XXX" solves problem. Dot (FILE$ = "SCH_LIST.") didn't help.
Re: BB4W can't open file with no extension!
Post by VBI on May 15th, 2012, 07:42am

Here's an example from one of my programs which works -

Code:
        infile$ = @dir$+"copyright"
        
        
        REM SAVE PROMs
        IF click% = 4 THEN
          REM Check if copyright file exists & add contents to prombuff%
          infile=OPENIN(infile$+".")
          IF infile THEN
            loc% = promsize%-100
            REPEAT
              temp%=BGET#infile
              prombuff%?loc% = temp%
              loc% = loc% + 1
            UNTIL EOF#infile


This loads a file named "copyright" which has no extension.
Re: BB4W can't open file with no extension!
Post by admin on May 15th, 2012, 08:15am

on May 15th, 2012, 06:37am, Endymion wrote:
This program doesn't work. Renaming file to "SCH_LIST.XXX" solves problem.

If you omit the 'dot' BBC BASIC assumes a default extension (often .BBC, but it depends on the context). If you want to open a file with no extension, simply use a trailing 'dot':

Code:
      FILE$ = "SCH_LIST."
      File1% = openin(FILE$)

See this Wiki article:
http://bb4w.wikispaces.com/Accessing+files+with+no+extension

Code:
if not File1% then end

That won't work because File1% is not a Boolean. Instead, test for the value being zero:

Code:
if File1%=0 then end

Richard.
Re: BB4W can't open file with no extension!
Post by Endymion on May 15th, 2012, 12:42pm

on May 15th, 2012, 08:15am, Richard Russell wrote:
If you omit the 'dot' BBC BASIC assumes a default extension (often .BBC, but it depends on the context).


.XXX and .BBC are equally suited to me.

Quote:
If you want to open a file with no extension, simply use a trailing 'dot':


Very strange. It was the first idea that came into my head. For some reason, did not work.

Quote:
Code:
if not File1% then end

That won't work because File1% is not a Boolean. Instead, test for the value being zero:

Code:
if File1%=0 then end

Richard.


I was guided by Rosetta Code - http://rosettacode.org/wiki/Ensure_that_a_file_exists#BBC_BASIC
Re: BB4W can't open file with no extension!
Post by admin on May 15th, 2012, 4:56pm

on May 15th, 2012, 12:42pm, Endymion wrote:
I was guided by Rosetta Code - http://rosettacode.org/wiki/Ensure_that_a_file_exists#BBC_BASIC

The code there is fine. It uses this:

Code:
      test% = OPENIN("input.txt")
      IF test% THEN

which is shorthand for:

Code:
      test% = OPENIN("input.txt")
      IF test%<>0 THEN

so to reverse the logic you need to change the <> into =:

Code:
      test% = OPENIN("input.txt")
      IF test%=0 THEN

Note that IF NOT test% does not (in general) reverse the result of IF test%. Think what happens if, for example, test% is 1:

Code:
      IF 1 THEN
        PRINT "Test passes"
      ENDIF

NOT 1 is -2 (try it) so we get:

Code:
      IF -2 THEN
        PRINT "Test passes"
      ENDIF

This is just the same in most other dialects of BASIC, and indeed other languages that don't have a native Boolean data type.

Richard.
Re: BB4W can't open file with no extension!
Post by Endymion on May 16th, 2012, 02:52am

on May 15th, 2012, 4:56pm, Richard Russell wrote:
This is just the same in most other dialects of BASIC, and indeed other languages that don't have a native Boolean data type.

Richard.


IMHO, it is absolutely illogical. I don't know all dialects of BASIC, but I remember, that Sinclair BASIC had much better bool-type-emulation: 0 = FALSE, 1 = TRUE, NOT 0 = 1, NOT (any number except zero) = 0. Why NOT (1) = -2 in BBC?
Re: BB4W can't open file with no extension!
Post by admin on May 16th, 2012, 08:30am

on May 16th, 2012, 02:52am, Endymion wrote:
IMHO, it is absolutely illogical.

On the contrary, it's absolutely logical! The NOT function inverts all the bits (this is standard binary logic) so if you look at the bit patterns you can see how it works:

1 = %00000000000000000000000000000001
NOT(1) = %11111111111111111111111111111110

Converting that binary value to decimal gives -2.

I think where you are going wrong is that you are confusing numbers with Booleans. If you stick with Booleans then everything works as you expect:

Code:
  PRINT TRUE
  PRINT FALSE
  PRINT NOT TRUE
  PRINT NOT FALSE

Running this shows that NOT TRUE is the same as FALSE (0), and NOT FALSE is the same as TRUE (-1).

If you are familiar with the C language you can do this (in C ~ is the binary NOT operator):

Code:
  int num = 1 ;
  int notnum = ~ num ;
  printf ("NOT(1) = %i", notnum) ;

If you run that it will print -2, demonstrating that BBC BASIC is by no means unusual in this respect.

(Later)
Also try this in Microsoft's QBASIC or QuickBASIC; you can guess what you will get:

Code:
PRINT NOT(1)


Richard.