C 해석 부탁드려도 될까엽?

학교 다닐때 잠깐 보던 C를 갑자기 다시 보게 됐씁니다..
아래 소스는 버클리 디비 예제에 나오는 건데엽.....
굴게 표시된 부분에서 왜 그렇게 처리를 했는지 몰겠네엽..
특히 for (t = rbuf, p = buf + (len - 2); p >= buf;) 요기서 왜 len-2를 해 줬는지....
아래는 레퍼런스 입니다.
http://www.database.sarang.net/database/dbm/BerkeleyDB/ref/simple_tut/close.html
많은 도움 바랍니다.

/*-
* See the file LICENSE for redistribution information.
*
* Copyright (c) 1997-2003
* Sleepycat Software. All rights reserved.
*
* $Id: ex_access.c,v 11.23 2003/01/08 04:43:53 bostic Exp $
*/

#include <sys/types.h>

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#ifdef _WIN32
extern int getopt(int, char * const *, const char *);
#else
#include <unistd.h>
#endif

#include <db.h>

#define DATABASE "access.db"
int main __P((int, char *[]));
int usage __P((void));

int
main(argc, argv)
int argc;
char *argv[];
{
extern int optind;
DB *dbp;
DBC *dbcp;
DBT key, data;
u_int32_t len;
int ch, ret, rflag;
char *database, *p, *t, buf[1024], rbuf[1024];
const char *progname = "ex_access"; /* Program name. */

rflag = 0;
while ((ch = getopt(argc, argv, "r")) != EOF)
switch (ch) {
case 'r':
rflag = 1;
break;
case '?':
default:
return (usage());
}
argc -= optind;
argv += optind;

/* Accept optional database name. */
database = *argv == NULL ? DATABASE : argv[0];

/* Optionally discard the database. */
if (rflag)
(void)remove(database);

/* Create and initialize database object, open the database. */
if ((ret = db_create(&dbp, NULL, 0)) != 0) {
fprintf(stderr,
"%s: db_create: %s\n", progname, db_strerror(ret));
return (EXIT_FAILURE);
}
dbp->set_errfile(dbp, stderr);
dbp->set_errpfx(dbp, progname);
if ((ret = dbp->set_pagesize(dbp, 1024)) != 0) {
dbp->err(dbp, ret, "set_pagesize");
goto err1;
}
if ((ret = dbp->set_cachesize(dbp, 0, 32 * 1024, 0)) != 0) {
dbp->err(dbp, ret, "set_cachesize");
goto err1;
}
if ((ret = dbp->open(dbp,
NULL, database, NULL, DB_BTREE, DB_CREATE, 0664)) != 0) {
dbp->err(dbp, ret, "%s: open", database);
goto err1;
}

/*
* Insert records into the database, where the key is the user
* input and the data is the user input in reverse order.
*/
memset(&key, 0, sizeof(DBT));
memset(&data, 0, sizeof(DBT));
for (;;) {
printf("input> ");
fflush(stdout);
if (fgets(buf, sizeof(buf), stdin) == NULL)
break;
if (strcmp(buf, "exit\n") == 0 || strcmp(buf, "quit\n") == 0)
break;
if ((len = strlen(buf)) <= 1)
continue;
/*******************************************************
요기를 잘 몰겠네엽...ㅡㅜ
***********************************/
for (t = rbuf, p = buf + (len - 2); p >= buf;)
*t++ = *p--; *t++ = '\0';

key.data = buf;
data.data = rbuf;
data.size = key.size = len - 1;

switch (ret =
dbp->put(dbp, NULL, &key, &data, DB_NOOVERWRITE)) {
case 0:
break;
default:
dbp->err(dbp, ret, "DB->put");
if (ret != DB_KEYEXIST)
goto err1;
break;
}
}
printf("\n");

/* Acquire a cursor for the database. */
if ((ret = dbp->cursor(dbp, NULL, &dbcp, 0)) != 0) {
dbp->err(dbp, ret, "DB->cursor");
goto err1;
}

/* Initialize the key/data pair so the flags aren't set. */
memset(&key, 0, sizeof(key));
memset(&data, 0, sizeof(data));

/* Walk through the database and print out the key/data pairs. */
while ((ret = dbcp->c_get(dbcp, &key, &data, DB_NEXT)) == 0)
printf("%.*s : %.*s\n",
(int)key.size, (char *)key.data,
(int)data.size, (char *)data.data);
if (ret != DB_NOTFOUND) {
dbp->err(dbp, ret, "DBcursor->get");
goto err2;
}

/* Close everything down. */
if ((ret = dbcp->c_close(dbcp)) != 0) {
dbp->err(dbp, ret, "DBcursor->close");
goto err1;
}
if ((ret = dbp->close(dbp, 0)) != 0) {
fprintf(stderr,
"%s: DB->close: %s\n", progname, db_strerror(ret));
return (EXIT_FAILURE);
}
return (EXIT_SUCCESS);

err2: (void)dbcp->c_close(dbcp);
err1: (void)dbp->close(dbp, 0);
return (EXIT_FAILURE);
}

int
usage()
{
(void)fprintf(stderr, "usage: ex_access [-r] [database]\n");
return (EXIT_FAILURE);
}