This function seeks within a file that was opened using mmioOpen.

#define INCL_MMIOOS2
#include <os2.h>

HMMIO    hmmio;    /*  Open file handle. */
LONG     lOffset;  /*  Offset in bytes. */
LONG     lOrigin;  /*  Origin of offset. */
LONG     rc;       /*  New file position. */

rc = mmioSeek(hmmio, lOffset, lOrigin);