StreamAdvancedRdWr (C++)

Description

This example demonstrates the use of TStreamReader's ReadBlock and DiscardBufferedData methods. ReadBlock is used to read a fixed number of characters from the reader and DiscardBufferedData is used when the underlying stream is seeked manually.

Code

void __fastcall TForm2::Button1Click(TObject *Sender)
{
	TStreamWriter* writer;
	TStreamReader* reader;
	TCharArray buffer;

	/* Create a writer */
	writer = new TStreamWriter("local_file.txt", false);

	/* Dump some data in */
	writer->WriteLine("Hello");
	writer->WriteLine("World!");

	/* Close the writer */
	delete writer;

	/* Create a reader */
	reader = new TStreamReader("local_file.txt");

	/* Prepare a buffer */
	buffer.set_length(5);

	/* Read first 5 characters */
	if (reader->ReadBlock(buffer, 0, buffer.Length) < buffer.Length)
		MessageDlg("Reading failed! Expected to read 5 characters!",
			mtError, TMsgDlgButtons() << mbOK, 0);

	/* And now, seek the stream back by 5 characters */
	int byteCount = reader->CurrentEncoding->GetByteCount(buffer);
	reader->BaseStream->Seek(-1 * byteCount, soFromCurrent);

	/* Reset the internal data buffer, since we modified the stream position */
	reader->DiscardBufferedData();

	MessageDlg("The original message was:" + reader->ReadLine() +
		" " + reader->ReadLine(), mtError, TMsgDlgButtons() << mbOK, 0);

	delete reader;
}

Uses

• System.Classes.TStreamReader.ReadBlock ( fr | de | ja )
• System.Classes.TStreamReader.DiscardBufferedData ( fr | de | ja )
• System.Classes.TTextReader.ReadBlock ( fr | de | ja )