Delphi How to replace data in Hex file

Question

To Load File content as hex i use this code in Delphi 7 :

procedure ReadFileAsHex(const AFileName: string; ADestination: TStrings);
var fs: TFileStream;
    buff: Byte;
    linecount: Byte;
    line: string;
begin
  linecount := 0;
  line := '';
  fs := TFileStream.Create(AFileName, fmOpenRead);
  try
    while fs.Position < fs.Size do begin
      fs.Read(buff, 1);
      line := line + IntToHex(buff, 2) + ' ';
      Inc(linecount);
      if linecount = 16 then begin
        ADestination.Add(line);
        line := '';
        linecount := 0;
      end;
    end;
    if Length(line) <> 0 then
      ADestination.Add(line);  
  finally
    fs.Free;
  end;
end;

This shows me Loaded File like this in Hex :

34 01 00 00 13 00 00 00 13 00 00 00 04 00 00 00
01 00 00 00 01 00 00 00 00 00 00 00 00 00 00 00
34 01 00 00 13 00 00 00 13 00 00 00 04 00 00 00
01 00 00 00 01 00 00 00 00 00 00 00 00 00 00 00

I want to Replace some data From actual file

For example I want to Replace Data From Offset(00000060) to Offset(00000070) for example with 00 all Is it possible or i will need some special component for this ?

Thanks

Answer 1

There's no such thing as "writing hex". Hex is just a way of representing a number and performing some math operations more easily. The hex value $00 is the exact same value as decimal 0, and if written to a file as numbers they're the exact same thing. The same is also true if you write $FF and decimal 255; they end up in the file as the same value, written the same way.

In other words, writing either of the following variables to a file will result in the same exact file content:

const
  DecimalZero = 0;
  HexZero = $0;

The same can be said for these:

const
  DecimalTwoFiftyFive = 255;
  HexTwoFiftyFive = $FF;

You can tell you're actually reading numeric (non-text) values by the fact that the code you've posted has to use IntToHex on the value to convert it to a hex string before it can add it to the line variable, which is declared as a string.

You're discussing writing binary (non-text) to the file, which simply means writing actual numeric values to the file rather than the textual representation of those numbers.

You just position the TFileStream to the point where you want to start writing, and write the number of bytes you want to the file. You have to open the stream in write mode, instead of readonly as your code does using fmOpenRead.

var
  fs: TFileStream;
  Buff: array of byte;
begin

  // Set length of buffer and initialize buffer to zeros
  SetLength(Buff, 10);
  FillChar(Buff[0], Length(Buff), #0);

  fs := TFileStream.Create(AFileName, fmOpenWrite);
  try
    fs.Position := 60;                 // Set to starting point of write
    fs.Write(Buff[0], Length(Buff));   // Write bytes to file
  finally
    fs.Free;
  end;
end;