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 */ 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 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