Working with Connected Storage Buffers

The Connected Storage API uses Windows::Storage::Streams::Buffer instances to pass data to and from an application. Because WinRT types cannot expose raw pointers, access to the data of a Buffer instance occurs through DataReader and DataWriter classes. However, Buffer also implements the COM interface IBufferByteAccess, which makes it possible to obtain a pointer directly to the buffer data.

To get a pointer to a Buffer instance’s data

Use reinterpret_cast to cast the Buffer instance as IUnknown.

IUnknown* unknown = reinterpret_cast<IUnknown*>(buffer);

Query the IUnknown interface for the IBufferByteAccess COM interface.

Microsoft::WRL::ComPtr<IBufferByteAccess> bufferByteAccess;
HRESULT hr = unknown->QueryInterface(_uuidof(IBufferByteAccess), &bufferByteAccess);
if (FAILED(hr))
return nullptr;

Use IBufferByteAccess::Buffer to get a pointer directly to the buffer’s data.
```
byte* bytes = nullptr;
bufferByteAccess->Buffer(&bytes);  
```

For example, the following code sample shows how to create a buffer that holds the current system time. Since buffers have a separate capacity and length value it is necessary to explicitly set both the capacity and length. By default, the length is 0.

inline byte* GetBufferData(Windows::Storage::Streams::IBuffer^ buffer)
{
    using namespace Windows::Storage::Streams;
    IUnknown* unknown = reinterpret_cast<IUnknown*>(buffer);
    Microsoft::WRL::ComPtr<IBufferByteAccess> bufferByteAccess;
    HRESULT hr = unknown->QueryInterface(_uuidof(IBufferByteAccess), &bufferByteAccess);
    if (FAILED(hr))
    return nullptr;
    byte* bytes = nullptr;
    bufferByteAccess->Buffer(&bytes);
    return bytes;
}

IBuffer^ WrapRawBuffer( void* ptr, size_t size ) 
{
    using namespace Windows::Storage::Streams;
 
    //uint32 size = sizeof(FILETIME);
    Buffer^ buffer = ref new Buffer(size);        
    buffer->Length = size;
    
    memcpy(GetBufferData(buffer),ptr,size);

 
    return buffer;

};