MMIOProc
The
MMIOProc function is a custom input/output (I/O) procedure installed by the
mmioInstallIOProc function.
MMIOProc is a placeholder for the application-defined function name. The address of
this function can be specified in the callback-address parameter of
mmioInstallIOProc.
LRESULT MMIOProc(
LPSTR lpmmioinfo,
|
|
UINT uMsg,
|
|
LONG lParam1,
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|
LONG lParam2
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);
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Parameters
lpmmioinfo
Points to an
MMIOINFO structure containing information about the open file.
The I/O procedure must maintain the
lDiskOffset member in this structure to indicate the file offset to the next read or
write location. The I/O procedure can use the
adwInfo[] member to store state information. The I/O procedure should not modify any
other members of the
MMIOINFO structure.
uMsg
Specifies a message indicating the requested I/O operation. Messages that can
be received include
MMIOM_OPEN,
MMIOM_CLOSE,
MMIOM_READ,
MMIOM_SEEK,
MMIOM_WRITE, and
MMIOM_WRITEFLUSH.
lParam1
Specifies an application-defined parameter for the message.
lParam2
Specifies an application-defined parameter for the message.
Return Values
The return value depends on the message specified by
uMsg. If the I/O procedure does not recognize a message, it should return zero.
Remarks
The four-character code specified by the
fccMMIOProc member in the
MMIOINFO structure associated with a file identifies a filename extension for a custom
storage system. When an application calls
mmioOpen with a filename such as "one.xyz+two", the I/O procedure associated with the
four-character code "XYZ" is called to open the "two" element of the file
"one.xyz".
The
mmioInstallIOProc function maintains a separate list of installed I/O procedures for each
Windows-based application. Therefore, different applications can use the same I/O
procedure identifier for different I/O procedures without conflict. However,
installing an I/O procedure globally enables any process to use the procedure.
If an application calls
mmioInstallIOProc more than once to register the same I/O procedure, then it must call
mmioInstallIOProc to remove the procedure once for each time it installed the procedure.
mmioInstallIOProc will not prevent an application from installing two different I/O procedures
with the same identifier, or installing an I/O procedure with one of the
predefined identifiers ("DOS ", "MEM "). The most recently installed procedure takes
precedence, and the most recently installed procedure is the first one to be
removed.
When searching for a specified I/O procedure, local procedures are searched
first, then global procedures.
See Also
MMIOINFO,
mmioInstallIOProc,
MMIOM_OPEN,
MMIOM_CLOSE,
MMIOM_READ,
MMIOM_SEEK,
MMIOM_WRITE,
MMIOM_WRITEFLUSH,
mmioOpen
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