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<a href="intro.html"><h2>SQLite C Interface</h2></a><h2>Function Auxiliary Data</h2><blockquote><pre>void *sqlite3_get_auxdata(sqlite3_context*, int N);
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void sqlite3_set_auxdata(sqlite3_context*, int N, void*, void (*)(void*));
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</pre></blockquote><p>
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The following two functions may be used by scalar SQL functions to
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associate metadata with argument values. If the same value is passed to
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multiple invocations of the same SQL function during query execution, under
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some circumstances the associated metadata may be preserved. This may
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be used, for example, to add a regular-expression matching scalar
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function. The compiled version of the regular expression is stored as
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metadata associated with the SQL value passed as the regular expression
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pattern. The compiled regular expression can be reused on multiple
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invocations of the same function so that the original pattern string
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does not need to be recompiled on each invocation.</p>
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<p>The sqlite3_get_auxdata() interface returns a pointer to the metadata
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associated by the sqlite3_set_auxdata() function with the Nth argument
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value to the application-defined function. If no metadata has been ever
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been set for the Nth argument of the function, or if the corresponding
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function parameter has changed since the meta-data was set,
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then sqlite3_get_auxdata() returns a NULL pointer.</p>
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<p>The sqlite3_set_auxdata() interface saves the metadata
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pointed to by its 3rd parameter as the metadata for the N-th
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argument of the application-defined function. Subsequent
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calls to sqlite3_get_auxdata() might return this data, if it has
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If it is not NULL, SQLite will invoke the destructor
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function given by the 4th parameter to sqlite3_set_auxdata() on
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the metadata when the corresponding function parameter changes
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or when the SQL statement completes, whichever comes first.</p>
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<p>SQLite is free to call the destructor and drop metadata on any
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parameter of any function at any time. The only guarantee is that
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the destructor will be called before the metadata is dropped.</p>
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<p>In practice, metadata is preserved between function calls for
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expressions that are constant at compile time. This includes literal
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values and <a href="../lang_expr.html#varparam">parameters</a>.</p>
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<p>These routines must be called from the same thread in which
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the SQL function is running.
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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>