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Split a binary file by searching for string

Posted on 1997-09-04
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Last Modified: 2010-04-04
I have a data file (binary) within which are contained
further data files. i.e.

GRIB.........(unknown number of chars)......GRIB.........
(unknown number of chars)......GRIB.........
(unknown number of chars)......GRIB.........
(unknown number of chars)......GRIB.........
(unknown number of chars)......
etc. etc.
GRIB.........
(unknown number of chars)......EOF

What I want to be able to do, is to read the datafile,
search for the first occurance of the string GRIB then
write GRIB and all the next characters out to file number
one, until GRIB occurs again. At this point, I will write
GRIB and all the characters out to file number two, until
GRIB occurs again of EOF. i.e. I want to split the
datafile into smaller files using the string GRIB as the
cutting point..

Anybody have a code segment (function) to do this ?
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Question by:iwatkins
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LVL 8

Accepted Solution

by:
ZifNab earned 200 total points
ID: 1343661
Hi itwatkins,

Maybe this helps, haven't tested it, so you have to test it yourself. Question, you constantly speak about chars. Is the file a char file? If so, you have to change to code a little bit.

How to call the function :

NewPos := SearchTextNext({File},{Start position},{Str})

{Start Position} = Position in file from where function has to start searching for {Str}

The value in NewPos gives the position of the first byte after {Str}

Type ByteFile : File of Byte;

function SearchTextNext(f:ByteFile;Pos:Integer;Str:ShortString):Integer
var J, OldPos : integer;
    Found : Boolean;
    I : Byte;
begin
 Found := False;
 J := 1;
 Seek(f,Pos);
 OldPos := FilePos(f);
 while not(EOF(f)) and Found then begin
  Read(f,I);
  if (Char(I) = Str[J]) and (OldPos=FilePos(f)-SizeOf(I)) then J := J+1
   else J := 1;
  OldPos := FilePos(f);
  if J = Length(Str)+1 then
   begin
    Found = True;
    Result := FilePos(f);
   end;
 end;
end;

Hope this is what you want.
Have fun,
c.u. ZifNab;
0
 
LVL 8

Expert Comment

by:ZifNab
ID: 1343662
Hi iwatkins,

Use function like this :

Euhm, better take backup of your data file!

Haven't tested this.

var OldFile, NewFile   : ByteFile;
    BeginPos, EndPos,I : Integer;
    chars              : Byte;

begin
  {$I-}
  AssignFile(OldFile, {FileName});
  FileMode := 0;  ( Set file access to read only }
  Reset(OldFile);
  {$I+}
  if IORESULT <> 0 then .... {Error}
   else begin
    BeginPos := SearchNextFile(OldFile,FilePos(OldFile),'GRIB');
    while not EOF(OldFile) do begin
     EndPos  := SearchNextFile(OldFile,FilePos(OldFile),'GRIB');
     Seek(OldFile, BeginPos);
  {Make newfile ready, change filename!! Not done in this demo!}
     {$I-} AssignFile(NewFile, {FileName})
           Rewrite(NewFile);
           for i := BeginPos To EndPos do begin
            read(OldFile,Chars);
            write(NewFile,Chars);
           end;
           CloseFile(NewFile);
     {$I+}
     if IORESULT <> 0 then ..... {OOOPS, ERROR}
     Seek(OldFile, EndPos);
    end;  
   end;
  {$I-}
  CloseFile(OldFile);
  {$I+}
end;

that's how you call it in your program. If this is what you needed and you need some answer, please be quick to ask them because I'm going on holiday soon.

Have fun,
In the sun,
c.u. ZifNab;
0
 
LVL 8

Expert Comment

by:ZifNab
ID: 1343663
And offcourse,
a fault!

changes :

EndPos := SearchNextFile(OldFile,BeginPos,'GRIB');

if IORESULT <> 0 then ..... {OOOPS, ERROR}
Seek(OldFile, EndPos);
BeginPos := EndPos;

Have fun,
c.u. ZifNab;

0
 
LVL 8

Expert Comment

by:ZifNab
ID: 1343664
So it worked! Great!

Have fun,
c.u. ZifNab;


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