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Appending a block to a file

I have developed a component to read an rpt (ReportSmith) file, and change the hard-coded paths within it so that my report points to the correct set of data.

It works perfectly, but I am reading it in as a File of Byte and writing it back to a new file, and all this takes a long time if it is a big file, especially if there are graphics within the Report.

I have discovered that I don't have to go through the whole file - just the first bit of it which has the embedded paths.

My question is - how can I stop reading in byte by byte when I have done the changes and just append the rest of the original file from that point. (OR if I were to block read the first part into memory, how would I read it and manipulate it in memory and then write it back).

ASKER CERTIFIED SOLUTION

vladika

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vladika

If you want test my procedure then create manually file c:\test.txt

APS NZ

ASKER

Hi Valdika - Thanks for your help

Sorry - but I forgot to mention I am using D1 and WFW 3.11, so I haven't got the SetString command.

I'm not sure if reading the data as strings would work because a lot of the bytes are outside the normal character range.

I am happy to read the first part in byte by byte as I have been doing, because the data to be read back may have added bytes or fewer bytes. I want to append the whole of the rest of the file in one hit if possible, or in large chunks after fixing up the first part of the file.

vladika

Hi Jdthedj

1) You may use not only string. Read, Write, ReadBuffer, WriteBuffer methods
works with ANY BUFFER, I use string as buffer only for example.

2) To copy the rest of one stream into other stream use CopyFrom method
Here is example

procedure TForm1.AnalizeAndReplace(SrcName, DstName: string);
var SrcStream, DstStream: TFileStream;
B: Byte;
S: string;
begin
SrcStream := TFileStream.Create(SrcName, fmOpenRead); { Source file stream }
try
DstStream := TFileStream.Create(DstName, fmCreate); { Dest file stream }
try
while SrcStream.Position < SrcStream.Size do { while not end of file }
begin
SrcStream.Read(B, 1); { read one Byte }
{ your code for analize B
for example search Char(B) = 'A'
when found insert into DstStream 'I found' and
copy rest }
if Char(B) = 'A' then
begin
S := 'I found';
DstStream.Write(S[1], Length(S)); { write S into Stream, I use string as buffer only for example}
Break; { exit from while }
end;
DstStream.Write(B, 1); {copy B into DstStream }
end;
{ copy rest }
if SrcStream.Position < SrcStream.Size then
DstStream.CopyFrom(SrcStream, SrcStream.Size - SrcStream.Position);
finally
DstStream.Free;
end;
finally
SrcStream.Free;
end;
end;

{ How to use }
procedure TForm1.Button1Click(Sender: TObject);
begin
AnalizeAndReplace('c:\src.dat', 'c:\dst.dat'); { src file name and dest file name }
end;

APS NZ

ASKER

Hi Vladika

Thanks a lot for all your help. You have explained it very clearly. It is a lot easier to program when you can understand what you are doing!