Performing Memory File I/O
The multimedia file I/O services let you treat a block of memory as a file. This can be useful if you already have a file image in memory. Memory files let you reduce the number of special-case conditions in your code because, for I/O purposes, you can treat memory files as if they were disk-based files. You can also use memory files with the clipboard.
As with I/O buffers, memory files can use memory allocated by the application or by the file I/O manager. In addition, memory files can be either expandable or nonexpandable. When the file I/O manager reaches the end of an expandable memory file, it expands the memory file by a predefined increment.
To open a memory file, use the mmioOpen function with the szFilename parameter set to NULL and the MMIO_READWRITE flag set in the dwOpenFlags parameter. Set the lpmmioinfo parameter to point to an MMIOINFO structure that has been set up as follows:
- Set the pIOProc member to NULL.
- Set the fccIOProc member to FOURCC_MEM.
- Set the pchBuffer member to point to the memory block. To request that the file I/O manager allocate the memory block, set pchBuffer to NULL.
- Set the cchBuffer member to the initial size of the memory block.
- Set the adwInfo member to the minimum expansion size of the memory block. For a nonexpandable memory file, set adwInfo to NULL.
- Set all other members to zero.
There are no restrictions on allocating memory for use as a nonexpandable memory file.