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 mmioOpen8DMA.3 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 MMIOINFO7F4X5_ structure that has been set up as follows:

  1.  Set the pIOProc member to NULL.

  2.  Set the fccIOProc member to FOURCC_MEM.

  3.  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.

  4.  Set the cchBuffer member to the initial size of the memory block.

  5.  Set the adwInfo member to the minimum expansion size of the memory block. For a nonexpandable memory file, set adwInfo to NULL.

  6.  Set all other members to zero.

There are no restrictions on allocating memory for use as a nonexpandable memory file.