IStream::CopyTo method (objidl.h)

Article
02/22/2024

The CopyTo method copies a specified number of bytes from the current seek pointer in the stream to the current seek pointer in another stream.

Syntax

HRESULT CopyTo(
  [in]  IStream        *pstm,
  [in]  ULARGE_INTEGER cb,
  [out] ULARGE_INTEGER *pcbRead,
  [out] ULARGE_INTEGER *pcbWritten
);

Parameters

[in] pstm

A pointer to the destination stream. The stream pointed to by pstm can be a new stream or a clone of the source stream.

[in] cb

The number of bytes to copy from the source stream.

[out] pcbRead

A pointer to the location where this method writes the actual number of bytes read from the source. You can set this pointer to NULL. In this case, this method does not provide the actual number of bytes read.

[out] pcbWritten

A pointer to the location where this method writes the actual number of bytes written to the destination. You can set this pointer to NULL. In this case, this method does not provide the actual number of bytes written.

Return value

This method can return one of these values.

Return code	Description
S_OK	The stream object was successfully copied.
E_PENDING	Asynchronous Storage only: Part or all of the data to be copied is currently unavailable.
STG_E_INVALIDPOINTER	The value of one of the pointer parameters is invalid.
STG_E_MEDIUMFULL	The stream is not copied because there is no space left on the storage device.
STG_E_REVERTED	The object has been invalidated by a revert operation above it in the transaction tree.

Remarks

The CopyTo method copies the specified bytes from one stream to another. It can also be used to copy a stream to itself. The seek pointer in each stream instance is adjusted for the number of bytes read or written. This method is equivalent to reading cb bytes into memory using ISequentialStream::Read and then immediately writing them to the destination stream using ISequentialStream::Write, although IStream::CopyTo will be more efficient.

The destination stream can be a clone of the source stream created by calling the IStream::Clone method.

If IStream::CopyTo returns an error, you cannot assume that the seek pointers are valid for either the source or destination. Additionally, the values of pcbRead and pcbWritten are not meaningful even though they are returned.

If IStream::CopyTo returns successfully, the actual number of bytes read and written are the same.

To copy the remainder of the source from the current seek pointer, specify the maximum large integer value for the cb parameter. If the seek pointer is the beginning of the stream, this operation copies the entire stream.

Requirements

Requirement	Value
Minimum supported client	Windows 2000 Professional [desktop apps \| UWP apps]
Minimum supported server	Windows 2000 Server [desktop apps \| UWP apps]
Target Platform	Windows
Header	objidl.h
Library	Uuid.lib
DLL	Ole32.dll