DosResetBuffer is used to write to disk (flush) the file system's cache buffers for a specific file handle. When called with a value of hex FFFF for the file handle, DosResetBuffer writes all files belonging to the requesting process to disk (this usage should be administered with care, so the user is not burdened with insertion and removal of a large number of removable media volumes).

When DosResetBuffer is called for single file handle, the directory entry for the file is updated as if the file had been closed. However, the file remains open.

DosResetBuffer can also be called with the name of a named pipe. The process that calls DosResetBuffer is blocked at one end of the pipe until all data it has written has been successfully read by the process at the other end of the pipe. This enables communicating processes to synchronize their dialogs.

The following code fragment opens a file, writes some data to the file's buffer, then writes the file's system buffer to the disk.

#define INCL_DOSFILEMGR          /* File Manager values */
#define INCL_DOSERRORS           /* DOS Error values    */
#include <os2.h>
#include <stdio.h>               /* Needed for printf   */
#include <string.h>              /* Needed for strcpy   */

int main( USHORT argc, PCHAR argv[] ) {

   HFILE  hfFileHandle   = 0L;       /* Handle for file being manipulated     */
   ULONG  ulAction       = 0;        /* Action taken (returned by DosOpen)    */
   ULONG  ulWrote        = 0;        /* Number of bytes written by DosWrite   */
   APIRET ulrc           = NO_ERROR;            /* Return code                */
   UCHAR  uchFileName[20]  = "MYDATA.DAT",      /* Name of file               */
          uchFileData[100] = " ";               /* Data to write to file      */

   /* Open the file MYDATA.DAT.  If the file already exists, replace it.
      If the file doesn't exist, create it.                           */

   ulrc = DosOpen(uchFileName,                    /* Path and file name         */
                  &hfFileHandle,                  /* File handle                */
                  &ulAction,                      /* Action taken (returned)    */
                  100L,                           /* File primary allocation    */
                  FILE_ARCHIVED |
                  FILE_NORMAL,                    /* File attributes            */
                  OPEN_ACTION_CREATE_IF_NEW |
                  OPEN_ACTION_REPLACE_IF_EXISTS,  /* Open function type         */
                  OPEN_SHARE_DENYREADWRITE |
                  OPEN_ACCESS_READWRITE,          /* Open mode of the file      */
                  0L);                            /* No extended attributes     */

   if (ulrc != NO_ERROR) {
      printf("DosOpen error: return code = %u\n", ulrc);
      return 1;
   }


   strcpy (uchFileData,
           "Data....");     /* This data will be written to file */

   ulrc = DosWrite (hfFileHandle,               /* File handle                  */
                    (PVOID) uchFileData,        /* String to be written         */
                    sizeof (uchFileData),       /* Size of string to be written */
                    &ulWrote);                  /* Bytes written (returned)     */

   if (ulrc != NO_ERROR) {
      printf("DosWrite error: return code = %u\n", ulrc);
      DosClose(hfFileHandle);         /* close the file */
      return 1;
   }

   ulrc = DosResetBuffer(hfFileHandle);

   if (ulrc != NO_ERROR) {
      printf("DosResetBuffer error: return code = %u\n", ulrc);
      DosClose(hfFileHandle);         /* close the file */
      return 1;
   }
   DosClose(hfFileHandle);            /* close the file */
   return NO_ERROR;
}