Basic string manipulation or number of lines in a file?

Ewon Support Ewon Flexy
#1

I have an application where I am recording a number of JSON objects to a file. At some point I read these objects back and publish them via MQTT. One object per payload is no problem but If I want to do multiple per payload I end up with a dangling comma.

I need to either remove 1 character from a string (a_string[:-1]) or know how many lines are in the file when I open it. Is Basic capable of doing either of these things?

#2

String manipulation is definitely possible in Basic. You’ll need to use LEN to get the length of the string, then String$(1 TO 5) to take a substring (in this case the first through fifth characters, 1-indexed). Here’s an example for removing the final character from a string:

A$ = "Test string,"
L% = LEN A$
PRINT A$(1 TO (L% - 1))
//Prints "Test string"

Determining how many lines are in a file should also be possible, though file parsing is a little trickier. If every line ends with a line feed character, this code should provide the number of lines:

OPEN "file:/usr/lines.txt" FOR BINARY INPUT AS 1
L% = 1
ReadNext:
  IF EOF 1 THEN GOTO ReadDone   //Go to ReadDone after reaching end of file
  CHAR$ = GET 1,1               //Get next character
  IF CHAR$ = CHR$(10) THEN      //If character is line feed
    L% = L% + 1                 //Then increment L%
  ENDIF
  GOTO ReadNext
ReadDone:
  PRINT L%
  CLOSE 1
1 Like
#3

Thanks. I did find the TO operator in the manual finally.

I thought about counting lines like that but did not want to read through the file twice.

The following code works for me:

$line$ = $line$ (1 TO LEN ($line$)-2)
#4

You’re using that code to count the lines in a file? Can you explain what the code is doing?

#5

No, I am using that code to remove the final comma and LF from the string I build from the file.

It was either doing that or counting the lines in the file so I know not to put the comma and LF in the string after the final entry from the file to begin with.

#6

Ah, that makes sense. Thanks for the explanation.