1<!--$Id: open.so,v 10.19 2003/10/18 19:16:01 bostic Exp $--> 2<!--Copyright (c) 1997,2008 Oracle. All rights reserved.--> 3<!--See the file LICENSE for redistribution information.--> 4<html> 5<head> 6<title>Berkeley DB Reference Guide: Opening databases within the environment</title> 7<meta name="description" content="Berkeley DB: An embedded database programmatic toolkit."> 8<meta name="keywords" content="embedded,database,programmatic,toolkit,btree,hash,hashing,transaction,transactions,locking,logging,access method,access methods,Java,C,C++"> 9</head> 10<body bgcolor=white> 11<table width="100%"><tr valign=top> 12<td><b><dl><dt>Berkeley DB Reference Guide:<dd>Environment</dl></b></td> 13<td align=right><a href="/env/create.html"><img src="/images/prev.gif" alt="Prev"></a><a href="/toc.html"><img src="/images/ref.gif" alt="Ref"></a><a href="/env/error.html"><img src="/images/next.gif" alt="Next"></a> 14</td></tr></table> 15<p align=center><b>Opening databases within the environment</b></p> 16<p>Once the environment has been created, database handles may be created 17and then opened within the environment. This is done by calling the 18<a href="/api_c/db_class.html">db_create</a> function and specifying the appropriate environment 19as an argument.</p> 20<p>File naming, database operations, and error handling will all be done as 21specified for the environment. For example, if the <a href="/api_c/env_open.html#DB_INIT_LOCK">DB_INIT_LOCK</a> 22or <a href="/api_c/env_open.html#DB_INIT_CDB">DB_INIT_CDB</a> flags were specified when the environment was 23created or joined, database operations will automatically perform all 24necessary locking operations for the application.</p> 25<p>The following is a simple example of opening two databases within a 26database environment:</p> 27<blockquote><pre> DB_ENV *dbenv; 28 DB *dbp1, *dbp2; 29 int ret; 30<p> 31 dbenv = NULL; 32 dbp1 = dbp2 = NULL; 33<p> 34 /* 35 * Create an environment and initialize it for additional error 36 * reporting. 37 */ 38 if ((ret = db_env_create(&dbenv, 0)) != 0) { 39 fprintf(errfp, "%s: %s\n", progname, db_strerror(ret)); 40 return (ret); 41 } 42<p> 43 dbenv->set_errfile(dbenv, errfp); 44 dbenv->set_errpfx(dbenv, progname); 45<p> 46 /* Open an environment with just a memory pool. */ 47 if ((ret = 48 dbenv->open(dbenv, home, DB_CREATE | DB_INIT_MPOOL, 0)) != 0) { 49 dbenv->err(dbenv, ret, "environment open: %s", home); 50 goto err; 51 } 52<p> 53 /* Open database #1. */ 54 if ((ret = db_create(&dbp1, dbenv, 0)) != 0) { 55 dbenv->err(dbenv, ret, "database create"); 56 goto err; 57 } 58 if ((ret = dbp1->open(dbp1, 59 NULL, DATABASE1, NULL, DB_BTREE, DB_CREATE, 0664)) != 0) { 60 dbenv->err(dbenv, ret, "DB->open: %s", DATABASE1); 61 goto err; 62 } 63<p> 64 /* Open database #2. */ 65 if ((ret = db_create(&dbp2, dbenv, 0)) != 0) { 66 dbenv->err(dbenv, ret, "database create"); 67 goto err; 68 } 69 if ((ret = dbp2->open(dbp2, 70 NULL, DATABASE2, NULL, DB_HASH, DB_CREATE, 0664)) != 0) { 71 dbenv->err(dbenv, ret, "DB->open: %s", DATABASE2); 72 goto err; 73 } 74<p> 75 return (0); 76<p> 77err: if (dbp2 != NULL) 78 (void)dbp2->close(dbp2, 0); 79 if (dbp1 != NULL) 80 (void)dbp2->close(dbp1, 0); 81 (void)dbenv->close(dbenv, 0); 82 return (1); 83}</pre></blockquote> 84<table width="100%"><tr><td><br></td><td align=right><a href="/env/create.html"><img src="/images/prev.gif" alt="Prev"></a><a href="/toc.html"><img src="/images/ref.gif" alt="Ref"></a><a href="/env/error.html"><img src="/images/next.gif" alt="Next"></a> 85</td></tr></table> 86<p><font size=1>Copyright (c) 1996,2008 Oracle. All rights reserved.</font> 87</body> 88</html> 89