73 lines
2.2 KiB
C
73 lines
2.2 KiB
C
|
/*
|
||
|
|
** 2016-08-09
|
||
|
|
**
|
||
|
|
** The author disclaims copyright to this source code. In place of
|
||
|
|
** a legal notice, here is a blessing:
|
||
|
|
**
|
||
|
|
** May you do good and not evil.
|
||
|
|
** May you find forgiveness for yourself and forgive others.
|
||
|
|
** May you share freely, never taking more than you give.
|
||
|
|
**
|
||
|
|
*************************************************************************
|
||
|
|
**
|
||
|
|
** This file demonstrates how to create an SQL function that is a pass-through
|
||
|
|
** for integer values (it returns a copy of its argument) but also saves the
|
||
|
|
** value that is passed through into a C-language variable. The address of
|
||
|
|
** the C-language variable is supplied as the second argument.
|
||
|
|
**
|
||
|
|
** This allows, for example, a counter to incremented and the original
|
||
|
|
** value retrieved, atomically, using a single statement:
|
||
|
|
**
|
||
|
|
** UPDATE counterTab SET cnt=remember(cnt,$PTR)+1 WHERE id=$ID
|
||
|
|
**
|
||
|
|
** Prepare the above statement once. Then to use it, bind the address
|
||
|
|
** of the output variable to $PTR using sqlite3_bind_pointer() with a
|
||
|
|
** pointer type of "carray" and bind the id of the counter to $ID and
|
||
|
|
** run the prepared statement.
|
||
|
|
**
|
||
|
|
** This implementation of the remember() function uses a "carray"
|
||
|
|
** pointer so that it can share pointers with the carray() extension.
|
||
|
|
**
|
||
|
|
** One can imagine doing similar things with floating-point values and
|
||
|
|
** strings, but this demonstration extension will stick to using just
|
||
|
|
** integers.
|
||
|
|
*/
|
||
|
|
#include "sqlite3ext.h"
|
||
|
|
SQLITE_EXTENSION_INIT1
|
||
|
|
#include <assert.h>
|
||
|
|
|
||
|
|
/*
|
||
|
|
** remember(V,PTR)
|
||
|
|
**
|
||
|
|
** Return the integer value V. Also save the value of V in a
|
||
|
|
** C-language variable whose address is PTR.
|
||
|
|
*/
|
||
|
|
static void rememberFunc(
|
||
|
|
sqlite3_context *pCtx,
|
||
|
|
int argc,
|
||
|
|
sqlite3_value **argv
|
||
|
|
){
|
||
|
|
sqlite3_int64 v;
|
||
|
|
sqlite3_int64 *ptr;
|
||
|
|
assert( argc==2 );
|
||
|
|
v = sqlite3_value_int64(argv[0]);
|
||
|
|
ptr = sqlite3_value_pointer(argv[1], "carray");
|
||
|
|
if( ptr ) *ptr = v;
|
||
|
|
sqlite3_result_int64(pCtx, v);
|
||
|
|
}
|
||
|
|
|
||
|
|
#ifdef _WIN32
|
||
|
|
__declspec(dllexport)
|
||
|
|
#endif
|
||
|
|
int sqlite3_remember_init(
|
||
|
|
sqlite3 *db,
|
||
|
|
char **pzErrMsg,
|
||
|
|
const sqlite3_api_routines *pApi
|
||
|
|
){
|
||
|
|
int rc = SQLITE_OK;
|
||
|
|
SQLITE_EXTENSION_INIT2(pApi);
|
||
|
|
rc = sqlite3_create_function(db, "remember", 2, SQLITE_UTF8, 0,
|
||
|
|
rememberFunc, 0, 0);
|
||
|
|
return rc;
|
||
|
|
}
|