DataWriter class

DataWriter class

Writes data to an output stream.


public ref class DataWriter sealed : IDataWriter,


The DataWriter class has these types of members:


The DataWriter class has these constructors.

DataWriter() Creates and initializes a new instance of the data writer.
DataWriter(IOutputStream) Creates and initializes a new instance of the data writer to an output stream.



The DataWriter class has these methods. With C#, Visual Basic, and C++, it also inherits methods from the Object class.

Close [C++, JavaScript]Closes the current stream and releases system resources.
DetachBuffer Detaches the buffer that is associated with the data writer.
DetachStream Detaches the stream that is associated with the data writer.
Dispose [C#, VB]Performs tasks associated with freeing, releasing, or resetting unmanaged resources.
FlushAsync Flushes data asynchronously.
MeasureString Gets the size of a string.
StoreAsync Commits data in the buffer to a backing store.
WriteBoolean Writes a Boolean value to the output stream.
WriteBuffer(IBuffer) Writes the contents of the specified buffer to the output stream.
WriteBuffer(IBuffer, UInt32, UInt32) Writes the specified bytes from a buffer to the output stream.
WriteByte Writes a byte value to the output stream.
WriteBytes Writes an array of byte values to the output stream.
WriteDateTime Writes a date and time value to the output stream.
WriteDouble Writes a floating-point value to the output stream.
WriteGuid Writes a GUID value to the output stream.
WriteInt16 Writes a 16-bit integer value to the output stream.
WriteInt32 Writes a 32-bit integer value to the output stream.
WriteInt64 Writes a 64-bit integer value to the output stream.
WriteSingle Writes a floating-point value to the output stream.
WriteString Writes a string value to the output stream.
WriteTimeSpan Writes a time-interval value to the output stream.
WriteUInt16 Writes a 16-bit unsigned integer value to the output stream.
WriteUInt32 Writes a 32-bit unsigned integer value to the output stream.
WriteUInt64 Writes a 64-bit unsigned integer value to the output stream.



The DataWriter class has these properties.

PropertyAccess typeDescription



Gets or sets the byte order of the data in the output stream.



Gets or sets the Unicode character encoding for the output stream.



Gets the size of the buffer that has not been used.



The following example shows how to write and read strings to an in-memory stream. For the full code sample, see Reading and writing data sample.

#include "pch.h"
#include "WriteReadStream.xaml.h"

using namespace Concurrency;
using namespace DataReaderWriter;
using namespace Platform;
using namespace Windows::Storage::Streams;
using namespace Windows::UI::Xaml;
using namespace Windows::UI::Xaml::Controls;
using namespace Windows::UI::Xaml::Navigation;

Array<String^>^ _inputElements = ref new Array<String^>
    "Hello", "World", "1 2 3 4 5", "Très bien!", "Goodbye"


    // Populate the text block with the input elements.
    ElementsToWrite->Text = "";
    for (unsigned int i = 0; i < _inputElements->Length; i++)
        ElementsToWrite->Text += _inputElements[i] + ";";

// Invoked when this page is about to be displayed in a Frame.
void WriteReadStream::OnNavigatedTo(NavigationEventArgs^ e)
    // Get a pointer to our main page.
    rootPage = MainPage::Current;

// This is the click handler for the 'Copy Strings' button.  Here we will parse the
// strings contained in the ElementsToWrite text block, write them to a stream using
// DataWriter, retrieve them using DataReader, and output the results in the
// ElementsRead text block.
void DataReaderWriter::WriteReadStream::TransferData(
Platform::Object^ sender, Windows::UI::Xaml::RoutedEventArgs^ e)
    // Initialize the in-memory stream where data will be stored.
    InMemoryRandomAccessStream^ stream = ref new InMemoryRandomAccessStream();

    // Create the DataWriter object backed by the in-memory stream.  When
    // dataWriter is deleted, it will also close the underlying stream.
    DataWriter^ dataWriter = ref new DataWriter(stream);
    dataWriter->UnicodeEncoding = UnicodeEncoding::Utf8;
    dataWriter->ByteOrder = ByteOrder::LittleEndian;

    // Create the data reader by using the input stream set at position 0 so that 
    // the stream will be read from the beginning regardless of where the position
    // the original stream ends up in after the store.
    IInputStream^ inputStream = stream->GetInputStreamAt(0);
    DataReader^ dataReader = ref new DataReader(inputStream);
    // The encoding and byte order need to match the settings of the writer 
    / we previously used.
    dataReader->UnicodeEncoding = UnicodeEncoding::Utf8;
    dataReader->ByteOrder = ByteOrder::LittleEndian;

    // Write the input data to the output stream.  Serialize the elements by writing
    // each string separately, preceded by its length.
    for (unsigned int i = 0; i < _inputElements->Length; i++) 
        unsigned int inputElementSize = dataWriter->MeasureString(_inputElements[i]);

    // Send the contents of the writer to the backing stream.
    create_task(dataWriter->StoreAsync()).then([this, dataWriter] (unsigned int bytesStored)
        // For the in-memory stream implementation we are using, the FlushAsync() call 
        // is superfluous, but other types of streams may require it.
        return dataWriter->FlushAsync();
    }).then([this, dataReader, stream] (bool flushOp)
        // Once we have written the contents successfully we load the stream.
        return dataReader->LoadAsync((unsigned int) stream->Size);
    }).then([this, dataReader] (task<unsigned int> bytesLoaded)
            // Check for possible exceptions that could have been thrown 
            // in the async call chain.

            String^ readFromStream = "";

            // Keep reading until we consume the complete stream.
            while (dataReader->UnconsumedBufferLength > 0)
                // Note that the call to ReadString requires a length of 
                // "code units" to read. This is the reason each string is 
                // preceded by its length when "on the wire".
                unsigned int bytesToRead = dataReader->ReadUInt32();
                readFromStream += dataReader->ReadString(bytesToRead) + "\n";

            // Populate the ElementsRead text block with the items we read from the stream
            ElementsRead->Text = readFromStream;
        catch (Exception^ e)
            ElementsRead->Text = "Error: " + e->Message;

Requirements (Windows 10 device family)

Device family

Universal, introduced version 10.0.10240.0

API contract

Windows.Foundation.UniversalApiContract, introduced version 1.0


Windows::Storage::Streams [C++]



Requirements (Windows 8.x and Windows Phone 8.x)

Minimum supported client

Windows 8 [Windows Store apps only]

Minimum supported server

Windows Server 2012 [Windows Store apps only]

Minimum supported phone

Windows Phone 8


Windows::Storage::Streams [C++]





See also

Reading and writing data sample
StreamSocket sample
Serializing and deserializing data sample (Windows 10)
File access sample (Windows 10)
DatagramSocket sample (Windows 10)
StreamSocket sample (Windows 10)
Custom USB device sample (Windows 10)



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