I get a little annoyed that yahoogroups strips out the leading spaces
which then greatly reduces the readibility of the code.
Maybe producing ">" prefixes on each line by replying to my own
message will overcome this.
I won't make a habit of this, this is just a test.
If anyone knows a way to preserve indents in posted code please let
me know.
> Your basic loop to scan a file is pretty simple and
> will look like this:
>
> function StringInFile(strFind, strFileName: string): boolean;
> const
> BUFSIZE = 8192;
> var
> fstm: TFileStream;
> numread: Longint;
> buffer: array [0..BUFSIZE-1] of char;
> szFind: array [0..255] of char;
> found: boolean;
> begin
> StrPCopy(szFind, strFind);
> found := False;
> fstm := TFileStream.Create(strFileName, fmOpenRead);
> repeat
> numread := fstrm.Read(Buffer, BUFSIZE);
> if BMFind(szFind, Buffer, numread) >= 0 then
> found := True
> else if numread = BUFSIZE then // more to scan
> fstm.Position := fstmPosition - (Length(strFind)-1);
> until found or (numread < BUFSIZE);
> fstm.Free;
> Result := found;
> end;
>
> 1) The reason for backing up fstm.Position by nearly the length
> of strFind is in case strFind crosses buffer boundaries.
>
> 2) The "BMFind" function used above is a Boyer-Moore search
> as shown below. This is the fastest string search known.
>
> function BMFind(szSubStr, buf: PChar; iBufSize: integer): integer;
> { Returns -1 if substring not found,
> or zero-based index into buffer if substring found }
> var
> iSubStrLen: integer;
> skip: array [char] of integer;
> found: boolean;
> iMaxSubStrIdx: integer;
> iSubStrIdx: integer;
> iBufIdx: integer;
> iScanSubStr: integer;
> mismatch: boolean;
> iBufScanStart: integer;
> ch: char;
> begin
> { Initialisations }
> found := False;
> Result := -1;
> { Check if trivial scan for empty string }
> iSubStrLen := StrLen(szSubStr);
> if iSubStrLen = 0 then
> begin
> Result := 0;
> Exit
> end;
>
> iMaxSubStrIdx := iSubStrLen - 1;
> { Initialise the skip table }
> for ch := Low(skip) to High(skip) do skip[ch] := iSubStrLen;
> for iSubStrIdx := 0 to (iMaxSubStrIdx - 1) do
> skip[szSubStr[iSubStrIdx]] := iMaxSubStrIdx - iSubStrIdx;
>
> { Scan the buffer, starting comparisons at the end of the
substring }
> iBufScanStart := iMaxSubStrIdx;
> while (not found) and (iBufScanStart < iBufSize) do
> begin
> iBufIdx := iBufScanStart;
> iScanSubStr := iMaxSubStrIdx;
> repeat
> mismatch := (szSubStr[iScanSubStr] <> buf[iBufIdx]);
> if not mismatch then
> if iScanSubStr > 0 then
> begin // more characters to scan
> Dec(iBufIdx); Dec(iScanSubStr)
> end
> else
> found := True;
> until mismatch or found;
> if found then
> Result := iBufIdx
> else
> iBufScanStart := iBufScanStart + skip[buf[iBufScanStart]];
> end;
> end;
>
> I have included a "wholeword_only" flag n the BMFind below.
> This confirms or rejects the "found" result, and will
> cause the loop to keep searching if match is rejected.
>
> function BMFind(szSubStr, buf: PChar; iBufSize: integer;
> wholeword_only: boolean): integer;
> { Returns -1 if substring not found,
> or zero-based index into buffer if substring found }
> var
> iSubStrLen: integer;
> skip: array [char] of integer;
> found: boolean;
> iMaxSubStrIdx: integer;
> iSubStrIdx: integer;
> iBufIdx: integer;
> iScanSubStr: integer;
> mismatch: boolean;
> iBufScanStart: integer;
> ch: char;
> begin
> found := False;
> Result := -1;
> iSubStrLen := StrLen(szSubStr);
> if iSubStrLen = 0 then
> begin
> Result := 0;
> Exit
> end;
>
> iMaxSubStrIdx := iSubStrLen - 1;
> { Initialise the skip table }
> for ch := Low(skip) to High(skip) do skip[ch] := iSubStrLen;
> for iSubStrIdx := 0 to (iMaxSubStrIdx - 1) do
> skip[szSubStr[iSubStrIdx]] := iMaxSubStrIdx - iSubStrIdx;
>
> { Scan the buffer, starting comparisons at the end of the
substring }
> iBufScanStart := iMaxSubStrIdx;
> while (not found) and (iBufScanStart < iBufSize) do
> begin
> iBufIdx := iBufScanStart;
> iScanSubStr := iMaxSubStrIdx;
> repeat
> mismatch := (szSubStr[iScanSubStr] <> buf[iBufIdx]);
> if not mismatch then
> if iScanSubStr > 0 then
> begin // more characters to scan
> Dec(iBufIdx); Dec(iScanSubStr)
> end
> else
> found := True;
> until mismatch or found;
> if found and wholeword_only then
> begin
> if (iBufIdx > 0) then
> found := not IsCharAlpha(buf[iBufIdx - 1]);
> if found then
> if iBufScanStart < (iBufSize - 1) then
> found := not IsCharAlpha(buf[iBufScanStart + 1]);
> end;
> if found then
> Result := iBufIdx
> else
> iBufScanStart := iBufScanStart + skip[buf[iBufScanStart]];
> end;
> end;
>
> Obviously you'll be tempted to increase BUFSIZE on the assumption
> that it will improve performance. My experience is that it does
> not, and that 8K is pretty optimum.
>
