GacUI/.github/KnowledgeBase/manual/vlppos/using-streams.md

Using Streams

Streams in this library are composable.

Let's say we need to read a file, it has a BOM at the beginning of the file to indicate the text encoding. Now we need to print the file line by line to the screen, and save the file in UTF-8 and UTF-16 without BOM, in two separated files.

Here is what we need:

• FileStreamfor accessing files.
• BroadcastStreamfor copy content to multiple streams.
• RecorderStreamfor reading data from a stream, and save what is read to another stream.
• EncoderStreamandDecoderStreamfor handling text encoding.We compose these streams in this way:

When we read text from theStreamReader, theStreamReaderreads data from theRecorderStream, which reads data from theDecoderStream.

At the same time, theRecorderStreamwrite all bytes that is read to theBroadcastStream, which writes data to twoEncoderStream.

DecoderStreamuses the assigned decoder to convert raw bytes from theFileStreamtowchar_t.EncoderStreamuses the assigned encoder to convertwchar_tto raw bytes and write to theFileStream.

By composing all streams together, what we need to do is just read text line by line from theStreamReader, and everything else will be done by all these connected streams.

#include <vlppos.h>

using namespace vl::console;
using namespace vl::stream;

int main()
{
    FileStream inputFileStream(L"C:/bom.txt", FileStream::ReadOnly);
    BomDecoder bomDecoder;
    DecoderStream inputDecoderStream(inputFileStream, bomDecoder);

    FileStream utf8FileStream(L"C:/utf8.txt", FileStream::WriteOnly);
    Utf8Encoder utf8Encoder;
    EncoderStream utf8EncoderStream(utf8FileStream, utf8Encoder);

    FileStream utf16FileStream(L"C:/utf16.txt", FileStream::WriteOnly);
    Utf16Encoder utf16Encoder;
    EncoderStream utf16EncoderStream(utf16FileStream, utf16Encoder);

    BroadcastStream broadcastStream;
    broadcastStream.Targets().Add(&utf8EncoderStream);
    broadcastStream.Targets().Add(&utf16EncoderStream);

    RecorderStream recorderStream(inputDecoderStream, broadcastStream);

    StreamReader reader(recorderStream);
    while (!reader.IsEnd())
    {
        Console::WriteLine(reader.ReadLine());
    }
}