This can reserve a large chunk of virtual address space and then commit memory within that address space as required. In this case, the preferred solution is to implement an IStream that uses memory allocated by the VirtualAlloc function instead of GlobalAlloc. If you are creating a stream object that is larger than the heap in your machine's memory and you are using a global memory handle, the compound file implementation calls the GlobalRealloc function internally whenever it needs more memory, which can be extremely inefficient. The specification of IStream defines more functionality that the COM implementation supports. Implement IStream on a container or object application when you require functionality not provided by the COM compound file implementation. There will be a subsequent call to IBindStatusCallback::OnDataAvailable with the grfBSC flag set to BSCF_LASTDATANOTIFICATION. Read is called to read all the available data and the bind operation is over (end-of-file). Returns E_PENDING if the bind operation has not completed, and IBindStatusCallback::OnDataAvailable will be called again when more data is available. Read is called to read all the available data. The client must continue to read all available data before returning from the IBindStatusCallback::OnDataAvailable method or else the bind operation is blocked, that is, read until S_FALSE or E_PENDING is returned.Įven if the client returns from IBindStatusCallback::OnDataAvailable at this point the bind operation continues and IBindStatusCallback::OnDataAvailable will be called again repeatedly until the binding finishes. Read is called to read partial data, that is, not all the available data. The following table shows a comparison between the behavior of the asynchronous ISequentialStream::Read method and IStream::Seek calls returned in IBindStatusCallback::OnDataAvailable in these two download models. Once released, the stream object is no longer valid and cannot be used.Ĭlients of asynchronous monikers can choose between a data-pull or data-push model for driving an asynchronous IMoniker::BindToStorage operation and for receiving asynchronous notifications. The IStream::Release method is similar to a close function on a file. Streams can remain open for long periods of time without consuming file system resources. There are also methods for committing and reverting changes on streams open in transacted mode and methods for restricting access to a range of bytes in the stream. The methods in this interface present your object's data as a contiguous sequence of bytes that you can read or write. The main difference between a stream object and a DOS file is that streams are not opened using a file handle, but through an IStream interface pointer. For example, each stream object has its own access rights and a seek pointer. The IStream interface defines methods similar to the MS-DOS FAT file functions. Simple data can be written directly to a stream, but most frequently, streams are elements nested within a storage object. ![]() Stream objects contain the data in a structured storage object, where storages provide the structure. The IStream interface supports reading and writing data to stream objects.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |