This function enables or disables buffered I/O, or changes the buffer or buffer size, for a file that was opened using mmioOpen.

#define INCL_MMIOOS2
#include <os2.h>

HMMIO     hmmio;      /*  Open file handle. */
PCHAR     pchBuffer;  /*  Pointer. */
LONG      cBytes;     /*  Buffer size. */
USHORT    usFlags;    /*  Flags. */
USHORT    rc;         /*  Return codes. */

rc = mmioSetBuffer(hmmio, pchBuffer, cBytes,
       usFlags);