Command of the Day: LOF()

[Walt Decker]

LOF stands for length of file.  What does it return, with what file types does it work, and why would one want to use it?

[gaslouk]

Hi

This function returns the length as number of bytes (or characters) contained in the open file referenced by #handle.

This example uses the LOF function to determine the size of an open file.

open "\folder.png" for input as #1
 qtyBytes = lof(#1)
 for x = 1 to qtyBytes
 next x
 close #1
 print qtyBytes ;
 end


Returns the length of the open file in characters and works with any file type.

Gaslouk

[Walt Decker]

That is a good start, but let's expand on your code a bit. I assume that Folder.png is a small graphic that displays a directory image when rendered in some graphics app. As such it will have some type of header information followed by blocks of either red, green, blue values or an unsigned long integer.

So, let's print it out in groups of 20 characters.

'
CounterMax = 20
Accumulator = 0
ChrIn$ = ""

open "\folder.png" for input as #1
 qtyBytes = lof(#1)
 for x = 1 to qtyBytes
   Accumulator = Accumulator + 1

   IF Accumulator = CounterMax THEN
     PRINT
     PRINT
     Accumulator = 0
   END IF
 
   INPUT #1, ChrIn$
   PRINT ChrIn$;
 next x
 close #1
 PRINT
 print qtyBytes
 end
'

How would you use LOF() to find the number of records(lines) in a text file so you could put those records in an array? How would you go about putting the records in the array without reading the file again? Remember that most text files are terminated with a CRLF, CR, or LF.

[Walt Decker]

Well, let us see what can be done with this. In another thread I have posted functions similar to those presented here.

The below code is NOT TESTED so there might be errors.

'
'  PUT SOME DATA IN A SEQUENTIAL FILE

CR$ = CHR$(13) + CHR$(10)

AryUbnd  = 0 '<--- upper bound of array
NumBytes = 0 '<--- number of bytes(characters) in file
RetVal   = 0 '<--- value returned from numeric function

DIM AryIn$(-1)

Stream$ = ""  '<--- text as a single variable from the text file

Fname$  = "SEQ_TEST.TXT"  '<--- name of sequential file

OPEN Fname$ FOR OUTPUT AS #1
PRINT #1, "The quick brown fox"
PRINT #1, "Peter Piper picked a peck"
PRINT #1, "Mary had a little lamb"
PRINT #1, "Little Miss Muffet sat on a tuffet"
PRINT #1, "The cow jumbped over the moon"
PRINT #1, "Humpty Dumpty sat on a wall"
CLOSE #1

T$ = "#OPN"  '<--- create a tag for MAPHANDLE

NumBytes = FN.OpenBinary(Fname$, T$)  '<--- open file in binary mode
Stream$ = FN.StreamIn$(NumBytes, T$)  '<--- get all text from the file
RetVal = FN.CloseFile(T$) '<--- close the file

AryUbnd = FN.ParseStr(Stream$, CR$) '<--- split the string into its parts
                                  'based on the indicated delimeter
IF AryUbnd THEN
 FOR I = 0 TO AryUbnd
   PRINT AryIn(I)
 NEXT I
END IF

END

'---------------------------------------------
'---------------------------------------------

FUNCTION FN.OpenBinary(NameIn$, Tag$)
'##############################################
'  ARGUMENTS:
'    NameIn$:  Path and file to open
'       Tag$:  Map name
'##############################################

NumBytes = 0
OPEN NameIn$ FOR BNARY AS #1  '<--- open the file.  If is does not exist
                             'it will be created
NumBytes = LOF(#1)  '<--- # of bytes(characters) in the file

MAPHANDLE #1, Tag$  '<--- rename the device handle

FN.OpenBinary = NumBytes
END FUNCTION

'---------------------------------------------
'---------------------------------------------

FUNCTION FN.CloseFile(Tag$)

NumBytes = LOF(#Tag$)
CLOSE #Tag$

FN.CloseFile = NumBytes
END FUNCTION

'---------------------------------------------
'---------------------------------------------

FUNCTION FN.StreamIn$(Size, Tag$)
'#####################################
'  ARGUMENTS:
'    Size:  # of bytes(characters) in file
'    Tag$:  Name of device
'#####################################

TxtIn$ = ""
TxtIn$ = INPUT$(#Tag$, Size)

FN.StreamIn$ = TxtIn$
END FUNCTION

'---------------------------------------------
'---------------------------------------------

FUNCTION FN.ParseStr(TxtIn$, Delm$)
'##########################################
'  ARGUMENTS:
'     TxtIn$: String to scan
'      Delm$: What to scan for
'##########################################

IF TxtIn$ = "" THEN  '<--- string is nul
 FN.ParseStr = -1
 EXIT FUNCTION
END IF

DlmLen = 0  '<--- # of characters in delimeter
Found  = 0  '<--- whether delimeter is found

I = -1      '<--- array element counter

Dlm$ = ","  '<--- default delimeter

IF Delm$ <> "" THEN Dlm$ = Delm$ '<--- change default

DlmLen = LEN(Dlm$)  '<--- set delimeter size

NumDlms = FN.ParseCount(TxtIn$, Dlm$) '<--- get # of delimiters in string
IF NumDlms THEN   '<--- set # of elements in array
 REDIM AryIn$(NumDlms)
ELSE
 FN.ParseStr = -1
 EXIT FUNCTION
END IF

 [BEGIN.PARSE]  '<--- scan for delimeter
Found = INSTR(TxtIn$, Dlm)

IF Found = 0 THEN GOTO [PARSE.ARY.END] '<--- exit scan

I = I + 1  '<--- increase array element counter
AryIn$(I) = LEFT$(TxtIn$, Found - 1) '<--- set text in array  
TxtIn$ = MID$(TxtIn$, Found + DlmLen  '<--- truncate TxtIn$
GOTO [BEGIN.PARSE] '<--- continue scan

 [PARSE.ARY.END]

FN.ParseStr = NumDlms
END FUNCTION

'---------------------------------------------
'---------------------------------------------

FUNCTION FN.ParseCount(Txt$, Delm$)
'#############################################
'  ARGUMENTS:
'      Txt$:  Text string to scan
'     Delm$:  What to scan for
'
'  NOTE:
'  If no delimier is found the function will return 1
'  if Txt$ is not nul otherwise it will return zero
'#############################################

IF Txt$ = "" THEN '<--- nothing to scan
 EXIT FUNCTION
END IF

DlmLen = 0 '<--- # of characters in Dlm$

ParseCount = 0 '<--- # of delimeters found

Found = 0 '<--- whether a delimeter is found
Strt  = 1 '<--- position to start scanning for delimiter

Dlm$ = "," '<--- default delimeter

IF Delm$ <> "" THEN Dlm$ = Delm$ '<--- change default

DlmLen = LEN(Dlm$)  '<--- delimeter characters

 [PARSE]  '<--- begin or continue scanning for delimter
Found = INSTR(Txt$, Dlm$, Strt)

IF Found = 0 THEN GOTO [END.PARSE] '<--- exit loop
 
ParseCount = ParseCount + 1 '<--- delimeter found so increase count
Strt = Found + DlmLen '<--- set new scan position
GOTO [PARSE] '<--- scan again

 [END.PARSE]
FN.ParseCount = ParseCount + 1
END FUNCTION
'

[gaslouk]

Hi.

Thank you for this valuable effort on your part.
But my level is much lower than your expectations. however I tried your code, fixed some mistakes I pointed out and it worked.

the results returned are these.

0

0

0

0

0

0

0

0

 

I believe it is correct because that particular file "SEQ_TEST.TXT" does not exist on my computer.

But even with a file that I read from my computer the result was the same.

Gaslouk

[Walt Decker]

First, the file is created on you computer by the app, so it should be there.

Second, looking at the original code I found a syntax error, so the printout will always be zero.

If you change this:
AryUbnd = FN.ParseStr(Stream$, CR$) '<--- split the string into its parts
                                  'based on the indicated delimeter
IF AryUbnd THEN
 FOR I = 0 TO AryUbnd
   PRINT AryIn(I)  '<---- ERROR HERE
 NEXT I
END IF

to this:
AryUbnd = FN.ParseStr(Stream$, CR$) '<--- split the string into its parts
                                  'based on the indicated delimeter
IF AryUbnd THEN
 FOR I = 0 TO AryUbnd
   PRINT AryIn$(I)   '<---- CHANGE
 NEXT I
END IF

you should get the contents of the file as elements of the array.

As for my expectations, I expect folks to go through the code, analyze it to the point where they understand what it does, and, if they do not understand, ask why I did it this way and, perhaps, is there another way. So keep plugging away.