Random access sequential files

[B+]

How sweet, you can access a sequential file for adding or editing lines like a Random Access file. Sweet because the strings are variable length!

'Random access sequential files.txt for JB v2.0 B+ 2018-10-16

fName$ = "Test sequential file.dat"
[editAdd]
cls
call showFile fName$
print
input "(0 to quite) Enter a line number to edit > ";lNum
if lNum = 0 then print "Goodbye!" : end
line input "Enter the the line to edit or add > ";eaLine$
call editAddLine fName$, lNum, eaLine$
goto [editAdd]
end

sub editAddLine fileName$, lineNum, newLine$
   if lineNum = 0 then exit sub  'no good

   'avoid file exist erors
   open fileName$ for append as #1
   close #1

   CRLF$ = chr$(13) + chr$(10)  'constant line ender

   'inhale file
   open fileName$ for input as #writeAtLine
   f$ = input$(#writeAtLine, lof(#writeAtLine))
   close #writeAtLine

   'process: count and record positions of CRLF's in file contents
   if right$(f$, 2) <> CRLF$ then f$ = f$ + CRLF$  'balance line counts by CRLF$ count
   pos = instr(f$, CRLF$) 'find end of first line
   while pos 'find end positions of remaining lines until run out of CRLF's
       if len(NLpos$) = 0 then NLpos$ = str$(pos) else NLpos$ = NLpos$ + " " + str$(pos) 'record crlf positions
       count = count + 1 'count crlf's
       pos = instr(f$, CRLF$, pos + 1) 'get next crlf if there is one
   wend

   'edit a line or add one or many?
   if lineNum > count then 'add line(s) to lineNum spot
       if lineNum = 1 then
           txt$ = newLine$
       else
           txt$ = f$
           while count < lineNum - 1
               txt$ = txt$ + CRLF$
               count = count + 1
           wend
           txt$ = txt$ + newLine$
       end if
   else  'edit the line
       if lineNum = 1 then txt$ = "" else txt$ = mid$(f$, 1, val(word$(NLpos$, lineNum - 1)) + 1)
       txt$ = txt$ + newLine$ + mid$(f$, val(word$(NLpos$, lineNum)))
   end if
   'remove last CRLF
   if right$(txt$, 2) = CRLF$ then txt$ = left$(txt$, len(txt$) - 2)

   'write to file in one go
   open fileName$ for output as #writeAtLine
       print #writeAtLine, txt$;   '(;) prevents extra CRLF
   close #writeAtLine
end sub

sub showFile filename$
   'avoid file exist erors
   open filename$ for append as #1
   close #1
   print filename$;":"
   open filename$ for input as #1
   while eof(#1) = 0
       i = i + 1
       line input #1, fline$
       print right$("   ";str$(i);": ", 6);fline$
   wend
   close #1
end sub


[carlgundel]

Consider the keyed dictionary code I posted on my blog. It lets you store and retrieve data by name. It uses a sequential file, but you don't need to care how the data is stored.

Use this link, and scroll down to find the code.

basicprogramming.blogspot.com/2016/

[B+]

I was talking about a plain old Sequential file and offering code to make lines accessible like a Random Access file.

There is a nice discussion of Dictionary code here: justbasiccom.proboards.com/thread/150/python-dict
(In fact, I still have code of the my mini-app version from 2016 when I used a Dictionary Editor for JB Command Words.)