Mega Code Archive
How to search a file for a specified text
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Title: How to search a file for a specified text
function ScanFile(const FileName: string;
const forString: string;
caseSensitive: Boolean): Longint;
{ returns position of string in file or -1, if not found }
const
BufferSize = $8001; { 32K+1 bytes }
var
pBuf, pEnd, pScan, pPos: PChar;
filesize: LongInt;
bytesRemaining: LongInt;
bytesToRead: Word;
F: file;
SearchFor: PChar;
oldMode: Word;
begin
Result := -1; { assume failure }
if (Length(forString) = 0) or (Length(FileName) = 0) then Exit;
SearchFor := nil;
pBuf := nil;
{ open file as binary, 1 byte recordsize }
AssignFile(F, FileName);
oldMode := FileMode;
FileMode := 0; { read-only access }
Reset(F, 1);
FileMode := oldMode;
try { allocate memory for buffer and pchar search string }
SearchFor := StrAlloc(Length(forString) + 1);
StrPCopy(SearchFor, forString);
if not caseSensitive then { convert to upper case }
AnsiUpper(SearchFor);
GetMem(pBuf, BufferSize);
filesize := System.Filesize(F);
bytesRemaining := filesize;
pPos := nil;
while bytesRemaining 0 do
begin
{ calc how many bytes to read this round }
if bytesRemaining = BufferSize then
bytesToRead := Pred(BufferSize)
else
bytesToRead := bytesRemaining;
{ read a buffer full and zero-terminate the buffer }
BlockRead(F, pBuf^, bytesToRead, bytesToRead);
pEnd := @pBuf[bytesToRead];
pEnd^ := #0;
{ scan the buffer. Problem: buffer may contain #0 chars! So we
treat it as a concatenation of zero-terminated strings. }
pScan := pBuf;
while pScan do
begin
if not caseSensitive then { convert to upper case }
AnsiUpper(pScan);
pPos := StrPos(pScan, SearchFor); { search for substring }
if pPos nil then
begin { Found it! }
Result := FileSize - bytesRemaining +
Longint(pPos) - Longint(pBuf);
Break;
end;
pScan := StrEnd(pScan);
Inc(pScan);
end;
if pPos nil then Break;
bytesRemaining := bytesRemaining - bytesToRead;
if bytesRemaining 0 then
begin
{ no luck in this buffers load. We need to handle the case of
the search string spanning two chunks of file now. We simply
go back a bit in the file and read from there, thus inspecting
some characters twice
}
Seek(F, FilePos(F) - Length(forString));
bytesRemaining := bytesRemaining + Length(forString);
end;
end; { While }
finally
CloseFile(F);
if SearchFor nil then StrDispose(SearchFor);
if pBuf nil then FreeMem(pBuf, BufferSize);
end;
end;
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