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 and the id of the counter to $ID and 25 ** run the prepared statement. 26 ** 27 ** One can imagine doing similar things with floating-point values and 28 ** strings, but this demonstration extension will stick to using just 29 ** integers. 30 */ 31 #include "sqlite3ext.h" 32 SQLITE_EXTENSION_INIT1 33 #include <assert.h> 34 35 /* 36 ** remember(V,PTR) 37 ** 38 ** Return the integer value V. Also save the value of V in a 39 ** C-language variable whose address is PTR. 40 */ 41 static void rememberFunc( 42 sqlite3_context *pCtx, 43 int argc, 44 sqlite3_value **argv 45 ){ 46 sqlite3_int64 v; 47 sqlite3_int64 ptr; 48 assert( argc==2 ); 49 v = sqlite3_value_int64(argv[0]); 50 ptr = sqlite3_value_int64(argv[1]); 51 *((sqlite3_int64*)ptr) = v; 52 sqlite3_result_int64(pCtx, v); 53 } 54 55 #ifdef _WIN32 56 __declspec(dllexport) 57 #endif 58 int sqlite3_remember_init( 59 sqlite3 *db, 60 char **pzErrMsg, 61 const sqlite3_api_routines *pApi 62 ){ 63 int rc = SQLITE_OK; 64 SQLITE_EXTENSION_INIT2(pApi); 65 rc = sqlite3_create_function(db, "remember", 2, SQLITE_UTF8, 0, 66 rememberFunc, 0, 0); 67 return rc; 68 } 69