BtRecExample.cpp   [plain text]

/*-
 * See the file LICENSE for redistribution information.
 *
 * Copyright (c) 1997,2008 Oracle.  All rights reserved.
 *
 * $Id: BtRecExample.cpp,v 12.6 2008/01/08 20:58:26 bostic Exp $
 */

#include <sys/types.h>

#include <errno.h>
#include <iostream>
#include <iomanip>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include <db_cxx.h>

using std::cout;
using std::cerr;

#define	DATABASE	"access.db"
#define	WORDLIST	"../test/wordlist"

const char *progname = "BtRecExample";		// Program name.

class BtRecExample
{
public:
	BtRecExample(FILE *fp);
	~BtRecExample();
	void run();
	void stats();
	void show(const char *msg, Dbt *key, Dbt *data);

private:
	Db *dbp;
	Dbc *dbcp;
};

BtRecExample::BtRecExample(FILE *fp)
{
	char *p, *t, buf[1024], rbuf[1024];
	int ret;

	// Remove the previous database.
	(void)remove(DATABASE);

	dbp = new Db(NULL, 0);

	dbp->set_error_stream(&cerr);
	dbp->set_errpfx(progname);
	dbp->set_pagesize(1024);			// 1K page sizes.

	dbp->set_flags(DB_RECNUM);			// Record numbers.
	dbp->open(NULL, DATABASE, NULL, DB_BTREE, DB_CREATE, 0664);

	//
	// Insert records into the database, where the key is the word
	// preceded by its record number, and the data is the same, but
	// in reverse order.
	//

	for (int cnt = 1; cnt <= 1000; ++cnt) {
		(void)sprintf(buf, "%04d_", cnt);
		if (fgets(buf + 4, sizeof(buf) - 4, fp) == NULL)
			break;
		u_int32_t len = (u_int32_t)strlen(buf);
		buf[len - 1] = '\0';
		for (t = rbuf, p = buf + (len - 2); p >= buf;)
			*t++ = *p--;
		*t++ = '\0';

		// As a convenience for printing, we include the null terminator
		// in the stored data.
		//
		Dbt key(buf, len);
		Dbt data(rbuf, len);

		if ((ret = dbp->put(NULL, &key, &data, DB_NOOVERWRITE)) != 0) {
			dbp->err(ret, "Db::put");
			if (ret != DB_KEYEXIST)
				throw DbException(ret);
		}
	}
}

BtRecExample::~BtRecExample()
{
	if (dbcp != 0)
		dbcp->close();
	dbp->close(0);
	delete dbp;
}

//
// Print out the number of records in the database.
//
void BtRecExample::stats()
{
	DB_BTREE_STAT *statp;

	dbp->stat(NULL, &statp, 0);
	cout << progname << ": database contains "
	     << (u_long)statp->bt_ndata << " records\n";

	// Note: must use free, not delete.
	// This struct is allocated by C.
	//
	free(statp);
}

void BtRecExample::run()
{
	db_recno_t recno;
	int ret;
	char buf[1024];

	// Acquire a cursor for the database.
	dbp->cursor(NULL, &dbcp, 0);

	//
	// Prompt the user for a record number, then retrieve and display
	// that record.
	//
	for (;;) {
		// Get a record number.
		cout << "recno #> ";
		cout.flush();
		if (fgets(buf, sizeof(buf), stdin) == NULL)
			break;
		recno = atoi(buf);

		//
		// Start with a fresh key each time,
		// the dbp->get() routine returns
		// the key and data pair, not just the key!
		//
		Dbt key(&recno, sizeof(recno));
		Dbt data;

		if ((ret = dbcp->get(&key, &data, DB_SET_RECNO)) != 0) {
			dbp->err(ret, "DBcursor->get");
			throw DbException(ret);
		}

		// Display the key and data.
		show("k/d\t", &key, &data);

		// Move the cursor a record forward.
		if ((ret = dbcp->get(&key, &data, DB_NEXT)) != 0) {
			dbp->err(ret, "DBcursor->get");
			throw DbException(ret);
		}

		// Display the key and data.
		show("next\t", &key, &data);

		//
		// Retrieve the record number for the following record into
		// local memory.
		//
		data.set_data(&recno);
		data.set_size(sizeof(recno));
		data.set_ulen(sizeof(recno));
		data.set_flags(data.get_flags() | DB_DBT_USERMEM);

		if ((ret = dbcp->get(&key, &data, DB_GET_RECNO)) != 0) {
			if (ret != DB_NOTFOUND && ret != DB_KEYEMPTY) {
				dbp->err(ret, "DBcursor->get");
				throw DbException(ret);
			}
		}
		else {
			cout << "retrieved recno: " << (u_long)recno << "\n";
		}
	}

	dbcp->close();
	dbcp = NULL;
}

//
// show --
//	Display a key/data pair.
//
void BtRecExample::show(const char *msg, Dbt *key, Dbt *data)
{
	cout << msg << (char *)key->get_data()
	     << " : " << (char *)data->get_data() << "\n";
}

int
main()
{
	FILE *fp;

	// Open the word database.
	if ((fp = fopen(WORDLIST, "r")) == NULL) {
		fprintf(stderr, "%s: open %s: %s\n",
			progname, WORDLIST, db_strerror(errno));
		return (EXIT_FAILURE);
	}

	try {
		BtRecExample app(fp);

		// Close the word database.
		(void)fclose(fp);
		fp = NULL;

		app.stats();
		app.run();
	}
	catch (DbException &dbe) {
		cerr << "Exception: " << dbe.what() << "\n";
		return (EXIT_FAILURE);
	}

	return (EXIT_SUCCESS);
}