Delphi - Streams

Streams are not very well documented. All streams are based on TStream which defines a number of virtual methods. 16 classes support the LoadFromStream and 15 support the SaveToStream methods, the one I use the most is TStrings.

Delphi uses Streams to read your components' default parameters from the *.dfm files (which are actually stored as a resource in the *.exe files).

Stream Classes | Streaming Utilities | TMemoryStream | XP RichEdit Design Problem

Stream Classes

It is fairly difficult to determine what stream classes are available - I have never found a list of them. (A partial list is available on the TStream help page.) The following hierarchy is based on searching the source files for class(TStream).

Class			Source File	Comment
TStream			classes.pas	Abstract base class
	TCustomMemoryStream		classes.pas
		TMemoryStream	classes.pas	Converts a buffer (block of memory) to/from a stream
		TResourceStream	classes.pas	Used to create (initialize) form components
	TStringStream		classes.pas	Converts a string to/from a stream
	THandleStream		classes.pas
		TFileStream	classes.pas
	TOleStream		axctrls.pas	Used to read and write via a COM interface
	TBlobStream		dbtables.pas	Used with BLOB fields
	TIBBlobStream		ibblob.pas	Interbase BLOB fields
	TIBDSBlobStream		ibcustomdataset.pas	Interbase Data Set BLOB fields
	TWinSocketStream		scktcomp.pas
IStream			ole2.pas	Abstract interface

Streaming Utilities

There are numerous utilities that use streams. These are only a few.

ObjectBinaryToText
ObjectTextToBinary

TMemoryStream

Using this is slightly confusing - it works on a buffer ... but buffer is never defined or explained. The following is based on trial and error.

procedure abc;
var
 temp: String;
 xx: TMemoryStream ;
 pc : pchar;
begin

  xx := TMemoryStream.Create;
  temp := '12345';
  pc := PChar(temp);

  xx.Write(        temp, length(temp)); // fails
  xx.Write(       @temp, length(temp)); // fails
  xx.Write(          pc, length(temp)); // fails

  xx.Write(     '12345', length(temp)); // works
  xx.Write(PChar(temp)^, length(temp)); // works
  xx.Write(         pc^, length(temp)); // works

end;

XP RichEdit Design Problem

I use rich edit controls to display text and to render *.rtf files. (*.rtf files are rendered only when they are read via a stream - my Help Generator application depends on this working.) Imagine my surprise when a working Windows 98 application crashed on Windows XP.

Using text files greater than 160 K, the following code works fine in Windows 98 but fails with a resource problem in Windows XP.

procedure TForm1.asText1Click(Sender: TObject);
var
 temp: String;
begin

  temp := PlainText_UIRichEdit.Lines.Text;
  Formatted_UIRichEdit.Lines.Text := temp ; // This line fails

end;

The following code works in both 98 and XP.

 
procedure TForm1.xx1Click(Sender: TObject);
var
  temp : String;
  xx   : TMemoryStream ;
  pc   : pchar;
  yy   : integer;
begin
  xx := TMemoryStream.Create;

  temp := PlainText_UIRichEdit.Lines.Text;
  pc := PChar(temp);
  yy := xx.Write(pc^, length(temp));
  xx.Position := 0;      // reset to the beginning of the stream
  Formatted_UIRichEdit.Lines.LoadFromStream(xx) ;

  xx.Free;

end;

This also works in both.

procedure TForm1.viaStringStream1Click(Sender: TObject);
var
  temp : String;
  xx   : TStringStream ;
begin

  temp := PlainText_UIRichEdit.Lines.Text;
  xx := TStringStream.Create(temp);
  xx.Position := 0;      // reset to the beginning of the stream
  Formatted_UIRichEdit.Lines.LoadFromStream(xx) ;

  xx.Free;

end;

This change also improved the program speed - from 12 seconds (string assignment) to 1 second (LoadFromStream) to copy the data.

Author: Robert Clemenzi - clemenzi@cpcug.org

Delphi - Streams

Stream Classes

Streaming Utilities

TMemoryStream

XP RichEdit Design Problem

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