Is it possible to parse file from end to beginning?

RAPID Programming
1

I can read and parse txt file from the beginning to the end this way:

Open “HOME:/Test.txt”,file\Read;
Rewind file;
WHILE EOF=TRUE DO
Read_Str:=ReadStr(file);
ENDWHILE

But how to read the file in reverse order? Is it possible using “ReadStr” function?

2

You could probably count the lines of the file with a FOR loop from beginning until EOF, then use ReadStr with \Line to start with the last line and FOR loop from the last line to the first line.

3

Seemed to work – as long as the line is not too long and can fit into a single string…

PROC exampleReadFileInReverse()
VAR string text;
VAR iodev infile;
VAR num lineCounter:=0;

Open “HOME:/test.txt”,infile\Read;

! count number of lines in the file
lineCounter:=0;
WHILE text <> EOF DO
IF text <> EOF THEN
text := ReadStr(infile\Line:=lineCounter+1);
IF text <> EOF lineCounter:=lineCounter+1;
ENDIF
ENDWHILE

TPWrite “File has “+NumToStr(lineCounter,0)+” lines.”;

! read file in reverse
FOR i FROM lineCounter TO 1 STEP -1 DO
text := ReadStr(infile\Line:=i);
TPWrite “Line #”+NumToStr(i,0)+" = "+text;
WaitTime 1;
ENDFOR

ENDPROC

4

Thanks for answer! I will definitely try your code. I figured out how to solve the problem through a temporary array. It’s working with any amount of strings in file.
Reverse_File.rar (488 Bytes)

5

Looks good.

To clarify: I was stating that you’d have a problem if a single line is long, rather than a large quantity of lines – make a test line with a hundred chars to see what I mean.