Locks and unlocks a range of an open file.

#define INCL_DOSFILEMGR
#include <os2.h>

HFILE        hFile;      /*  File handle. */
PFILELOCK    pflUnlock;  /*  Address of the structure containing the offset and length of a range to be unlocked. */
PFILELOCK    pflLock;    /*  Address of the structure containing the offset and length of a range to be locked. */
ULONG        timeout;    /*  The maximum time, in milliseconds, that the process is to wait for the requested locks. */
ULONG        flags;      /*  Flags that describe the action to be taken. */
APIRET       ulrc;       /*  Return Code. */

ulrc = DosSetFileLocks(hFile, pflUnlock, pflLock,
         timeout, flags);