MMIOM_GETCF
The MMIOM_GETCF message is sent to a Multimedia I/O (MMIO) procedure to request the file handle (`HMMCF`) of the RIFF compound file container that contains the specific element or resource associated with the open `hmmio` session.
Syntax
hmmcf = (HMMCF)mmioSendMessage(hmmio, MMIOM_GETCF, lParam1, lParam2);
Parameters
- pmmioinfo (PMMIOINFO)
- A pointer to an MMIOINFO data structure maintaining the current state of the open file.
- usMsg (USHORT)
- The message identifier, set to `MMIOM_GETCF`.
- lParam1 (LONG)
- This parameter is not used.
- lParam2 (LONG)
- This parameter is not used.
Return Value
- hmmcf (ULONG)
- Returns the handle to the RIFF compound file context:
- HMMCF: A valid handle to the compound file's CTOC (Compound File Table of Contents) structure enclosing the target media element.
- NULL: Returned if an error occurs, or if the open media element is a standard standalone file rather than an element within a compound container.
Remarks
- **Compound File Architecture**: OS/2 Multimedia Presentation Manager relies on RIFF compound files (bundles of multiple distinct resource elements, like audio, images, or metadata subtitles, packaged into a single physical archive).
- **Navigational Mapping**: When an application resolves an individual sub-element stream inside a bundle, it uses its localized `hmmio` context. Sending MMIOM_GETCF allows the system to walk backwards up the execution tree to expose the parent container context (`HMMCF`).
- **CTOC Linkage**: The handle retrieved corresponds directly to the active Compound File Table of Contents (CTOC), which charts where individual elements begin, end, and interleave across the master container payload block.