SQLite scalar function with context example

odd.c

void odd (sqlite3_context *ctx, int argc, sqlite3_value **argv){		
	int *pCounter = (int*)sqlite3_get_auxdata(ctx, 0);
	if (pCounter == 0) {
		pCounter = sqlite3_malloc(sizeof(*pCounter));
		if (pCounter == 0) 
			return sqlite3_result_error_nomem(ctx);
		
		*pCounter = sqlite3_value_type(argv[0]) == SQLITE_NULL ? 0 : sqlite3_value_int(argv[0]);
		sqlite3_set_auxdata(ctx, 0, pCounter, sqlite3_free);
	} else {
		++*pCounter;
	}
	
	sqlite3_result_int(ctx, *pCounter % 2);
}