4 ** The author disclaims copyright to this source code. In place of
5 ** a legal notice, here is a blessing:
7 ** May you do good and not evil.
8 ** May you find forgiveness for yourself and forgive others.
9 ** May you share freely, never taking more than you give.
11 *************************************************************************
13 ** This file demonstrates how to create an SQL function that is a pass-through
14 ** for integer values (it returns a copy of its argument) but also saves the
15 ** value that is passed through into a C-language variable. The address of
16 ** the C-language variable is supplied as the second argument.
18 ** This allows, for example, a counter to incremented and the original
19 ** value retrieved, atomically, using a single statement:
21 ** UPDATE counterTab SET cnt=remember(cnt,$PTR)+1 WHERE id=$ID
23 ** Prepare the above statement once. Then to use it, bind the address
24 ** of the output variable to $PTR (using sqlite3_bind_pointer()) and
25 ** bind the id of the counter to $ID and run the prepared statement.
27 ** One can imagine doing similar things with floating-point values and
28 ** strings, but this demonstration extension will stick to using just
31 #include "sqlite3ext.h"
32 SQLITE_EXTENSION_INIT1
38 ** Return the integer value V. Also save the value of V in a
39 ** C-language variable whose address is PTR.
41 static void rememberFunc(
42 sqlite3_context
*pCtx
,
49 v
= sqlite3_value_int64(argv
[0]);
50 ptr
= sqlite3_value_pointer(argv
[1]);
52 sqlite3_result_int64(pCtx
, v
);
58 int sqlite3_remember_init(
61 const sqlite3_api_routines
*pApi
64 SQLITE_EXTENSION_INIT2(pApi
);
65 rc
= sqlite3_create_function(db
, "remember", 2, SQLITE_UTF8
, 0,