mmioOpen

  • Article

The mmioOpen function opens a file for unbuffered or buffered I/O. The file can be a standard file, a memory file, or an element of a custom storage system. The handle returned by mmioOpen is not a standard file handle; do not use it with any file I/O functions other than multimedia file I/O functions.

HMMIO mmioOpen(
  LPTSTR szFilename,       
  LPMMIOINFO lpmmioinfo,  
  DWORD dwOpenFlags       
);

Parameters

szFilename

Pointer to a string containing the file name of the file to open. If no I/O procedure is specified to open the file, the file name determines how the file is opened, as follows:

  • If the file name does not contain a plus sign (+), it is assumed to be the name of a standard file (that is, a file whose type is not HMMIO).
  • If the file name is of the form EXAMPLE.EXT+ABC, the extension EXT is assumed to identify an installed I/O procedure which is called to perform I/O on the file. For more information, see mmioInstallIOProc.
  • If the file name is NULL and no I/O procedure is given, the adwInfo member of the MMIOINFO structure is assumed to be the standard (non-HMMIO) file handle of a currently open file.

The file name should not be longer than 128 bytes, including the terminating NULL character.

When opening a memory file, set szFilename to NULL.

lpmmioinfo

Pointer to an MMIOINFO structure containing extra parameters used by mmioOpen. Unless you are opening a memory file, specifying the size of a buffer for buffered I/O, or specifying an uninstalled I/O procedure to open a file, this parameter should be NULL. If this parameter is not NULL, all unused members of the MMIOINFO structure it references must be set to zero, including the reserved members.

dwOpenFlags

Flags for the open operation. The MMIO_READ, MMIO_WRITE, and MMIO_READWRITE flags are mutually exclusive — only one should be specified. The MMIO_COMPAT, MMIO_EXCLUSIVE, MMIO_DENYWRITE, MMIO_DENYREAD, and MMIO_DENYNONE flags are file-sharing flags. The following values are defined.

Value Meaning
MMIO_ALLOCBUF Opens a file for buffered I/O. To allocate a buffer larger or smaller than the default buffer size (8K, defined as MMIO_DEFAULTBUFFER), set the cchBuffer member of the MMIOINFO structure to the desired buffer size. If cchBuffer is zero, the default buffer size is used. If you are providing your own I/O buffer, this flag should not be used.
MMIO_COMPAT Opens the file with compatibility mode, allowing any process on a given machine to open the file any number of times. If the file has been opened with any of the other sharing modes, mmioOpen fails.
MMIO_CREATE Creates a new file. If the file already exists, it is truncated to zero length. For memory files, this flag indicates the end of the file is initially at the start of the buffer.
MMIO_DELETE Deletes a file. If this flag is specified, szFilename should not be NULL. The return value is TRUE (cast to HMMIO) if the file was deleted successfully or FALSE otherwise. Do not call the mmioClose function for a file that has been deleted. If this flag is specified, all other flags that open files are ignored.
MMIO_DENYNONE Opens the file without denying other processes read or write access to the file. If the file has been opened in compatibility mode by any other process, mmioOpen fails.
MMIO_DENYREAD Opens the file and denies other processes read access to the file. If the file has been opened in compatibility mode or for read access by any other process, mmioOpen fails.
MMIO_DENYWRITE Opens the file and denies other processes write access to the file. If the file has been opened in compatibility mode or for write access by any other process, mmioOpen fails.
MMIO_EXCLUSIVE Opens the file and denies other processes read and write access to the file. If the file has been opened in any other mode for read or write access, even by the current process, mmioOpen fails.
MMIO_EXIST Determines whether the specified file exists and creates a fully qualified file name from the path specified in szFilename. The file name is placed back into szFilename. The return value is TRUE (cast to HMMIO) if the qualification was successful and the file exists or FALSE otherwise. The file is not opened, and the function does not return a valid multimedia file I/O file handle, so do not attempt to close the file.
MMIO_GETTEMP Creates a temporary file name, optionally using the parameters passed in szFilename. For example, you can specify "C:F" to create a temporary file residing on drive C, starting with letter "F". The resulting file name is placed in the buffer pointed to by szFilename. The return value is MMSYSERR_NOERROR (cast to HMMIO) if the temporary file name was created successfully or MMIOERR_FILENOTFOUND otherwise. The file is not opened, and the function does not return a valid multimedia file I/O file handle, so do not attempt to close the file. This flag overrides all other flags.
MMIO_PARSE Creates a fully qualified file name from the path specified in szFilename. The file name is placed back into szFilename. The return value is TRUE (cast to HMMIO) if the qualification was successful or FALSE otherwise. The file is not opened, and the function does not return a valid multimedia file I/O file handle, so do not attempt to close the file. If this flag is specified, all flags that open files are ignored.
MMIO_READ Opens the file for reading only. This is the default if MMIO_WRITE and MMIO_READWRITE are not specified.
MMIO_READWRITE Opens the file for reading and writing.
MMIO_WRITE Opens the file for writing only.

Return Values

Returns a handle of the opened file. If the file cannot be opened, the return value is NULL. If lpmmioinfo is not NULL, the wErrorRet member of the MMIOINFO structure will contain one of the following error values.

Value Description
MMIOERR_ACCESSDENIED The file is protected and cannot be opened.
MMIOERR_INVALIDFILE Another failure condition occurred. This is the default error for an open-file failure.
MMIOERR_NETWORKERROR The network is not responding to the request to open a remote file.
MMIOERR_PATHNOTFOUND The directory specification is incorrect.
MMIOERR_SHARINGVIOLATION The file is being used by another application and is unavailable.
MMIOERR_TOOMANYOPENFILES The number of files simultaneously open is at a maximum level. The system has run out of available file handles.

Remarks

If lpmmioinfo references an MMIOINFO structure, set up the members of that structure as described below. All unused members must be set to zero, including reserved members.

  • To request that a file be opened with an installed I/O procedure, set fccIOProc to the four-character code of the I/O procedure, and set pIOProc to NULL.
  • To request that a file be opened with an uninstalled I/O procedure, set IOProc to point to the I/O procedure, and set fccIOProc to NULL.
  • To request that mmioOpen determine which I/O procedure to use to open the file based on the file name contained in szFilename, set fccIOProc and pIOProc to NULL. This is the default behavior if no MMIOINFO structure is specified.
  • To open a memory file using an internally allocated and managed buffer, set pchBuffer to NULL, fccIOProc to FOURCC_MEM, cchBuffer to the initial size of the buffer, and adwInfo to the incremental expansion size of the buffer. This memory file will automatically be expanded in increments of the number of bytes specified in adwInfo when necessary. Specify the MMIO_CREATE flag for the dwOpenFlags parameter to initially set the end of the file to be the beginning of the buffer.
  • To open a memory file using an application-supplied buffer, set pchBuffer to point to the memory buffer, fccIOProc to FOURCC_MEM, cchBuffer to the size of the buffer, and adwInfo to the incremental expansion size of the buffer. The expansion size in adwInfo should be nonzero only if pchBuffer is a pointer obtained by calling the GlobalAlloc and GlobalLock functions; in this case, the GlobalReAlloc function will be called to expand the buffer. In other words, if pchBuffer points to a local or global array or a block of memory in the local heap, adwInfo must be zero. Specify the MMIO_CREATE flag for the dwOpenFlags parameter to initially set the end of the file to be the beginning of the buffer. Otherwise, the entire block of memory is considered readable.
  • To use a currently open standard file handle (that is, a file handle that does not have the HMMIO type) with multimedia file I/O services, set fccIOProc to FOURCC_DOS, pchBuffer to NULL, and adwInfo to the standard file handle. Offsets within the file will be relative to the beginning of the file and are not related to the position in the standard file at the time mmioOpen is called; the initial multimedia file I/O offset will be the same as the offset in the standard file when mmioOpen is called. To close the multimedia file I/O file handle without closing the standard file handle, pass the MMIO_FHOPEN flag to mmioClose.

You must call mmioClose to close a file opened by using mmioOpen. Open files are not automatically closed when an application exits.

Requirements

**  Windows NT/2000/XP:** Included in Windows NT 3.1 and later.
**  Windows 95/98/Me:** Included in Windows 95 and later.
**  Header:** Declared in Mmsystem.h; include Windows.h.
**  Library:** Use Winmm.lib.
**  Unicode:** Implemented as Unicode and ANSI versions on Windows NT/2000/XP.

See Also

ABC, mmioInstallIOProc, MMIOINFO, mmioClose, IOProc, GlobalAlloc, GlobalLock, GlobalReAlloc