IStream::Read - OLE Programmer's Reference (ole.hlp)

IStream::Read

Reads a specified number of bytes from the stream object into memory starting at the current seek pointer.

HRESULT Read(

void * pv,	//Pointer to buffer into which the stream is read
ULONG cb,	//Specifies the number of bytes to read
ULONG * pcbRead	//Pointer to location that contains actual number of bytes read
);

Parameters
pv

[in]Points to the buffer into which the stream is read. If an error occurs, this value is NULL.

[in]Specifies the number of bytes of data to attempt to read from the stream object.

pcbRead

[out]Pointer to a location where this method writes the actual number of bytes read from the stream object. You can set this pointer to NULL to indicate that you are not interested in this value. In this case, this method does not provide the actual number of bytes read.

Return Values
S_OK

Data was successfully read from the stream object.

S_FALSE

The data could not be read from the stream object.

STG_E_ACCESSDENIED

The caller does not have sufficient permissions for reading this stream object.

STG_E_INVALIDPOINTER

One of the pointer values is invalid.

STG_E_REVERTED

The object has been invalidated by a revert operation above it in the transaction tree.

Comments
This method reads bytes from this stream object into memory. The stream object must be opened in STGM_READ mode. This method adjusts the seek pointer by the actual number of bytes read.

The number of bytes actually read is returned in the pcbRead parameter.

Notes to Callers
The actual number of bytes read can be fewer than the number of bytes requested if an error occurs or if the end of the stream is reached during the read operation.

The OLE-provided implementation of IStream returns S_OK if the end of the stream was reached during the read. (This is the same as the "end of file" behavior found in the MS-DOS FAT file system.

Some implementations might return an error if the end of the stream is reached during the read. You must be prepared to deal with the error return or S_OK return values on end of stream reads.

See Also
STGMOVE, IStorage::OpenStream, IStream::Write

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