IStream::SetSize

Changes the size of the stream object.

HRESULT SetSize(

ULARGE_INTEGER libNewSize	//Specifies the new size of the stream object
);

Parameter
libNewSize

[in]Specifies the new size of the stream as a number of bytes.

Return Values
S_OK

The size of the stream object was successfully changed.

STG_E_MEDIUMFULL

The stream size is not changed because there is no space left on the storage device.

STG_E_INVALIDFUNCTION

The value of the libNewSize parameter is not valid. Since streams cannot be greater than 2 (32) bytes in the OLE-provided implementation, the high DWORD of libNewSize must be 0. If it is nonzero, this parameter is not valid.

Comments
This method changes the size of the stream object. You can use this method to preallocate space for the stream. If the libNewSize parameteris larger than the current stream size, the stream is extended to the indicated size by filling the intervening space with bytes of undefined value. This operation is similar to the IStream::Write method if the seek pointer is past the current end-of-stream.

If the libNewSize parameter is smaller than the current stream, then the stream is truncated to the indicated size.

The seek pointer is not affected by the change in stream size.

Calling IStream::SetSize is an effective way of trying to obtain a large chunk of contiguous space. However, in the OLE-provided implementation of streams, there is no guarantee that the space will be contiguous.