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<! "@(#)open.so 10.8 (Sleepycat) 11/1/98">
<!Copyright 1997, 1998 by Sleepycat Software, Inc. All rights reserved.>
<html>
<body bgcolor=white>
<head>
<title>Berkeley DB Reference Guide: Simple Tutorial</title>
<meta name="description" content="Berkeley DB: An embedded database programmatic toolkit.">
<meta name="keywords" content="embedded,database,programmatic,toolkit,b+tree,btr
ee,hash,hashing,transaction,transactions,locking,logging,access method,access me
thods,java,C,C++">
</head>
<h3>Berkeley DB Reference Guide: Simple Tutorial</h3>
<p>
<h1 align=center>Opening a database</h1>
<p>
Opening a database is done using the Berkeley DB <a href="../../api_c/Db/open.html">db_open</a> interface.
<p>
The <a href="../../api_c/Db/open.html">db_open</a> interface takes seven arguments:
<dl compact>
<p><dt>file<dd>The name of the database file to be opened.
<p><dt>type<dd>The type of database to open.
This value will be one of the three access methods Berkeley DB supports:
DB_BTREE, DB_HASH, or DB_RECNO, or the special value DB_UNKNOWN, which
allows you to open an existing file without knowing its type.
<p><dt>flags<dd>Various flags that modify the behavior of <a href="../../api_c/Db/open.html">db_open</a>.
In our simple case, we care only about one of these flags: DB_CREATE.
This flag behaves similarly to the POSIX 1003.1 flag to the open system
call, causing Berkeley DB to create the underlying database if it does not
yet exist.
<p><dt>mode<dd>The file mode of any underlying files that <a href="../../api_c/Db/open.html">db_open</a> will create.
The mode behaves similarly to the POSIX 1003.1 mode argument to the open
system call, and specifies an octal value for read, write and execute
permission. Obviously, all we care about is reading and writing!
<p><dt>dbenv<dd>Additional arguments describing the database environment in which the
database will be opened.
This argument isn't applicable now, and so we will leave it unspecified.
<p><dt>dbinfo<dd>Additional information describing the database file to be opened.
This argument is used to specify things like the underlying page size
or a comparison function for B+tree databases.
We don't need to specify any of these things for our simple example,
and so we will leave it unspecified.
<p><dt>dbpp<dd>A location in which to store the database handle that <a href="../../api_c/Db/open.html">db_open</a> will
return on success.
</dl>
<p>
Here's what the code to call <a href="../../api_c/Db/open.html">db_open</a> looks like:
<a name="startcode">
<p><ul><pre><b>#include <sys/types.h>
#include <stdio.h>
#include <db.h>
<p>
#define DATABASE "access.db"
<p>
int
main()
{
extern int errno;
DB *dbp;
<p>
if ((errno = db_open(DATABASE,
DB_BTREE, DB_CREATE, 0664, NULL, NULL, &dbp)) != 0) {
fprintf(stderr, "db: %s: %s\n", DATABASE, strerror(errno));
exit (1);
}
</b>
</pre></ul><p>
<p>
As you can see, we're opening a database named <b>access.db</b>.
The underlying database is a B+tree, and since we've specified DB_CREATE,
we'll create it if it doesn't already exist. The mode of any files we
create is 0664 (i.e., readable and writeable by the owner and the group,
and readable by everyone else).
<p>
If the call to <a href="../../api_c/Db/open.html">db_open</a> is successful, the variable <b>dbp</b>
will contain a database handle that will be used to access the underlying
database.
<p>
<a href="../../ref/simple_tut/errors.html"><img src="../../images/prev.gif"></a>
<a href="../../ref/toc.html"><img src="../../images/toc.gif"></a>
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