142 lines
5.8 KiB
HTML
142 lines
5.8 KiB
HTML
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<link href="../sqlite.css" rel="stylesheet">
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<title>Low-Level Control Of Database Files</title>
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<!-- keywords: {file control} sqlite3_file_control -->
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<div class=nosearch>
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<a href="intro.html"><h2>SQLite C Interface</h2></a>
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<h2>Low-Level Control Of Database Files</h2>
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</div>
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<blockquote><pre>
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int sqlite3_file_control(sqlite3*, const char *zDbName, int op, void*);
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</pre></blockquote>
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<p>
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The <a href="../c3ref/file_control.html">sqlite3_file_control()</a> interface makes a direct call to the
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xFileControl method for the <a href="../c3ref/io_methods.html">sqlite3_io_methods</a> object associated
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with a particular database identified by the second argument. The
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name of the database is "main" for the main database or "temp" for the
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TEMP database, or the name that appears after the AS keyword for
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databases that are added using the <a href="../lang_attach.html">ATTACH</a> SQL command.
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A NULL pointer can be used in place of "main" to refer to the
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main database file.
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The third and fourth parameters to this routine
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are passed directly through to the second and third parameters of
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the xFileControl method. The return value of the xFileControl
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method becomes the return value of this routine.</p>
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<p>A few opcodes for <a href="../c3ref/file_control.html">sqlite3_file_control()</a> are handled directly
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by the SQLite core and never invoke the
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sqlite3_io_methods.xFileControl method.
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The <a href="../c3ref/c_fcntl_begin_atomic_write.html#sqlitefcntlfilepointer">SQLITE_FCNTL_FILE_POINTER</a> value for the op parameter causes
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a pointer to the underlying <a href="../c3ref/file.html">sqlite3_file</a> object to be written into
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the space pointed to by the 4th parameter. The
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<a href="../c3ref/c_fcntl_begin_atomic_write.html#sqlitefcntljournalpointer">SQLITE_FCNTL_JOURNAL_POINTER</a> works similarly except that it returns
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the <a href="../c3ref/file.html">sqlite3_file</a> object associated with the journal file instead of
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the main database. The <a href="../c3ref/c_fcntl_begin_atomic_write.html#sqlitefcntlvfspointer">SQLITE_FCNTL_VFS_POINTER</a> opcode returns
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a pointer to the underlying <a href="../c3ref/vfs.html">sqlite3_vfs</a> object for the file.
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The <a href="../c3ref/c_fcntl_begin_atomic_write.html#sqlitefcntldataversion">SQLITE_FCNTL_DATA_VERSION</a> returns the data version counter
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from the pager.</p>
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<p>If the second parameter (zDbName) does not match the name of any
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open database file, then SQLITE_ERROR is returned. This error
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code is not remembered and will not be recalled by <a href="../c3ref/errcode.html">sqlite3_errcode()</a>
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or <a href="../c3ref/errcode.html">sqlite3_errmsg()</a>. The underlying xFileControl method might
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also return SQLITE_ERROR. There is no way to distinguish between
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an incorrect zDbName and an SQLITE_ERROR return from the underlying
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xFileControl method.</p>
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<p>See also: <a href="../c3ref/c_fcntl_begin_atomic_write.html">file control opcodes</a>
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</p><p>See also lists of
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<a href="objlist.html">Objects</a>,
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<a href="constlist.html">Constants</a>, and
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<a href="funclist.html">Functions</a>.</p>
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