Question

for write something in a file i use for example this code:

procedure MyProc (... );
const
  BufSize = 65535;
var
  FileSrc, FileDst: TFileStream;
  StreamRead: Cardinal;
  InBuf, OutBuf: Array [0..bufsize] of byte;
begin
  .....
  FileSrc := TFileStream.Create (uFileSrc, fmOpenRead Or fmShareDenyWrite);
  try
    FileDst := TFileStream.Create (uFileTmp, fmCreate);
    try
      StreamRead := 0;
      while ((iCounter < iFileSize) or (StreamRead = Cardinal(BufSize))) 
      begin
        StreamRead := FileSrc.Read (InBuf, BufSize);
        Inc (iCounter, StreamRead);
      end;
    finally
      FileDst.Free;
    end;
  finally
    FileSrc.Free;
  end;
end;

And for I/O file i use a array of byte, and so is all ok, but when i use a string, for example declaring:

InBuf, OutBuf: string  // in delphi xe2 = unicode string

then not work. In sense that file not write nothing. I have understood why, or just think to have understood it.
I think that problem maybe is why string contain just a pointer to memory and not static structure; correct?
In this case, there is some solution for solve it? In sense, is possible to do something for i can to write a file using string and not vector? Or i need necessary use a vector?
If possible, can i can to do ?
Thanks very much.

Answer 1

There are two issues with using strings. First of all you want to use RawByteString so that you ensure the use of byte sized character elements – a Unicode string has elements that are two bytes wide. And secondly you need to dereference the string which is really just a pointer.

But I wonder why you would prefer strings to the stack allocated byte array.

procedure MyProc (... );
const
  BufSize = 65536;
var
  FileSrc, FileDst: TFileStream;
  StreamRead: Cardinal;
  InBuf: RawByteString;
begin
  .....
  FileSrc := TFileStream.Create (uFileSrc, fmOpenRead Or fmShareDenyWrite);
  try
    FileDst := TFileStream.Create (uFileTmp, fmCreate);
    try
      SetLength(InBuf, BufSize);
      StreamRead := 0;
      while ((iCounter < iFileSize) or (StreamRead = Cardinal(BufSize))) 
      begin
        StreamRead := FileSrc.Read (InBuf[1], BufSize);
        Inc (iCounter, StreamRead);
      end;
    finally
      FileDst.Free;
    end;
  finally
    FileSrc.Free;
  end;
end;

Note: Your previous code declared a buffer of 65536 bytes, but you only ever used 65535 of them. Probably not what you intended.