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<h1>DbEnv::log_get</h1>
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<h3><pre>
#include <db_cxx.h>
<p>
int
DbEnv::log_get(DbLsn *lsn, Dbt *data, u_int32_t flags);
</pre></h3>
<h1>Description</h1>
<p>The DbEnv::log_get method implements a cursor inside of the log,
retrieving records from the log according to the <b>lsn</b> and
<b>flags</b> arguments.
<p>The data field of the <b>data</b> structure is set to the record
retrieved and the size field indicates the number of bytes in the record.
See <a href="../api_cxx/dbt_class.html">Dbt</a> for a description of other fields in the <b>data</b>
structure. When multiple threads are using the returned log handle
concurrently, one of the <a href="../api_cxx/dbt_class.html#DB_DBT_MALLOC">DB_DBT_MALLOC</a>, <a href="../api_cxx/dbt_class.html#DB_DBT_REALLOC">DB_DBT_REALLOC</a> or
<a href="../api_cxx/dbt_class.html#DB_DBT_USERMEM">DB_DBT_USERMEM</a> flags must be specified for any <a href="../api_cxx/dbt_class.html">Dbt</a> used
for data retrieval.
<p>The <b>flags</b> argument must be set to exactly one of the following values:
<p><dl compact>
<p><dt><a name="DB_CHECKPOINT">DB_CHECKPOINT</a><dd>The last record written with the DB_CHECKPOINT flag specified to the
<a href="../api_cxx/log_put.html">DbEnv::log_put</a> method is returned in the <b>data</b> argument. The
<b>lsn</b> argument is overwritten with the <a href="../api_cxx/lsn_class.html">DbLsn</a> of the record
returned. If no record has been previously written with the DB_CHECKPOINT
flag specified, the first record in the log is returned.
<p>If the log is empty, the DbEnv::log_get method will return <a href="../ref/program/errorret.html#DB_NOTFOUND">DB_NOTFOUND</a>.
<p><dt><a name="DB_FIRST">DB_FIRST</a><dd>The first record from any of the log files found in the log directory
is returned in the <b>data</b> argument.
The <b>lsn</b> argument is overwritten with the <a href="../api_cxx/lsn_class.html">DbLsn</a> of the
record returned.
<p>If the log is empty, the DbEnv::log_get method will return <a href="../ref/program/errorret.html#DB_NOTFOUND">DB_NOTFOUND</a>.
<p><dt><a name="DB_LAST">DB_LAST</a><dd>The last record in the log is returned in the <b>data</b> argument.
The <b>lsn</b> argument is overwritten with the <a href="../api_cxx/lsn_class.html">DbLsn</a> of the
record returned.
<p>If the log is empty, the DbEnv::log_get method will return <a href="../ref/program/errorret.html#DB_NOTFOUND">DB_NOTFOUND</a>.
<p><dt><a name="DB_NEXT">DB_NEXT</a><dd>The current log position is advanced to the next record in the log and that
record is returned in the <b>data</b> argument.
The <b>lsn</b> argument is overwritten with the <a href="../api_cxx/lsn_class.html">DbLsn</a> of the
record returned.
<p>If the pointer has not been initialized via DB_FIRST, DB_LAST, DB_SET,
DB_NEXT, or DB_PREV, DbEnv::log_get will return the first record in the log.
If the last log record has already been returned or the log is empty, the
DbEnv::log_get method will return <a href="../ref/program/errorret.html#DB_NOTFOUND">DB_NOTFOUND</a>.
<p>If the log was opened with the DB_THREAD flag set, calls to
DbEnv::log_get with the DB_NEXT flag set will return EINVAL.
<p><dt><a name="DB_PREV">DB_PREV</a><dd>The current log position is moved to the previous record in the log and that
record is returned in the <b>data</b> argument.
The <b>lsn</b> argument is overwritten with the <a href="../api_cxx/lsn_class.html">DbLsn</a> of the
record returned.
<p>If the pointer has not been initialized via DB_FIRST, DB_LAST, DB_SET,
DB_NEXT, or DB_PREV,
DbEnv::log_get will return the last record in the log.
If the first log record has already been returned or the log is empty, the
DbEnv::log_get method will return <a href="../ref/program/errorret.html#DB_NOTFOUND">DB_NOTFOUND</a>.
<p>If the log was opened with the DB_THREAD flag set, calls to
DbEnv::log_get with the DB_PREV flag set will return EINVAL.
<p><dt><a name="DB_CURRENT">DB_CURRENT</a><dd>Return the log record currently referenced by the log.
<p>If the log pointer has not been initialized via DB_FIRST, DB_LAST, DB_SET,
DB_NEXT, or DB_PREV, or if the log was opened with the DB_THREAD flag set,
DbEnv::log_get will return EINVAL.
<p><dt><a name="DB_SET">DB_SET</a><dd>Retrieve the record specified by the <b>lsn</b> argument. If the
specified <a href="../api_cxx/lsn_class.html">DbLsn</a> is invalid (e.g., does not appear in the log)
DbEnv::log_get will return EINVAL.
</dl>
<p>Otherwise, the DbEnv::log_get method either returns a non-zero error value or throws an exception that
encapsulates a non-zero error value on failure, and returns 0 on success.
<h1>Errors</h1>
<p>The DbEnv::log_get method may fail and throw an exception or return a non-zero error for the following conditions:
<p><dl compact>
<p><dt>EINVAL<dd>An invalid flag value or parameter was specified.
<p>The DB_FIRST flag was specified and no log files were found.
</dl>
<p>The DbEnv::log_get method may fail and throw an exception or return a non-zero error for errors specified for other Berkeley DB and C library or system methods.
If a catastrophic error has occurred, the DbEnv::log_get method may fail and either
return <a href="../ref/program/errorret.html#DB_RUNRECOVERY">DB_RUNRECOVERY</a> or throw an exception encapsulating
<a href="../ref/program/errorret.html#DB_RUNRECOVERY">DB_RUNRECOVERY</a>, in which case all subsequent Berkeley DB calls will fail
in the same way.
<h3>Class</h3>
<a href="../api_cxx/dbenv_class.html">DbEnv</a>
<h1>See Also</h1>
<a href="../api_cxx/env_set_lg_bsize.html">DbEnv::set_lg_bsize</a>,
<a href="../api_cxx/env_set_lg_max.html">DbEnv::set_lg_max</a>,
<a href="../api_cxx/log_archive.html">DbEnv::log_archive</a>,
<a href="../api_cxx/log_compare.html">DbEnv::log_compare</a>,
<a href="../api_cxx/log_file.html">DbEnv::log_file</a>,
<a href="../api_cxx/log_flush.html">DbEnv::log_flush</a>,
<a href="../api_cxx/log_get.html">DbEnv::log_get</a>,
<a href="../api_cxx/log_put.html">DbEnv::log_put</a>,
<a href="../api_cxx/log_register.html">DbEnv::log_register</a>,
<a href="../api_cxx/log_stat.html">DbEnv::log_stat</a>
and
<a href="../api_cxx/log_unregister.html">DbEnv::log_unregister</a>.
</tt>
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