1 /*
2 ** 2016-08-09
3 **
4 ** The author disclaims copyright to this source code. In place of
5 ** a legal notice, here is a blessing:
6 **
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.
10 **
11 *************************************************************************
12 **
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.
17 **
18 ** This allows, for example, a counter to incremented and the original
19 ** value retrieved, atomically, using a single statement:
20 **
21 ** UPDATE counterTab SET cnt=remember(cnt,$PTR)+1 WHERE id=$ID
22 **
23 ** Prepare the above statement once. Then to use it, bind the address
24 ** of the output variable to $PTR using sqlite3_bind_pointer() with a
25 ** pointer type of "carray" and bind the id of the counter to $ID and
26 ** run the prepared statement.
27 **
28 ** This implementation of the remember() function uses a "carray"
29 ** pointer so that it can share pointers with the carray() extension.
30 **
31 ** One can imagine doing similar things with floating-point values and
32 ** strings, but this demonstration extension will stick to using just
33 ** integers.
34 */
35 #include "sqlite3ext.h"
36 SQLITE_EXTENSION_INIT1
37 #include <assert.h>
38
39 /*
40 ** remember(V,PTR)
41 **
42 ** Return the integer value V. Also save the value of V in a
43 ** C-language variable whose address is PTR.
44 */
rememberFunc(sqlite3_context * pCtx,int argc,sqlite3_value ** argv)45 static void rememberFunc(
46 sqlite3_context *pCtx,
47 int argc,
48 sqlite3_value **argv
49 ){
50 sqlite3_int64 v;
51 sqlite3_int64 *ptr;
52 assert( argc==2 );
53 v = sqlite3_value_int64(argv[0]);
54 ptr = sqlite3_value_pointer(argv[1], "carray");
55 if( ptr ) *ptr = v;
56 sqlite3_result_int64(pCtx, v);
57 }
58
59 #ifdef _WIN32
60 __declspec(dllexport)
61 #endif
sqlite3_remember_init(sqlite3 * db,char ** pzErrMsg,const sqlite3_api_routines * pApi)62 int sqlite3_remember_init(
63 sqlite3 *db,
64 char **pzErrMsg,
65 const sqlite3_api_routines *pApi
66 ){
67 int rc = SQLITE_OK;
68 SQLITE_EXTENSION_INIT2(pApi);
69 rc = sqlite3_create_function(db, "remember", 2, SQLITE_UTF8, 0,
70 rememberFunc, 0, 0);
71 return rc;
72 }
73