Question

Is it possible to re-use the sqlite3 output?I have query like this :

            error = sqlite3_prepare_v2(conn,SQL_STMT_GET_FILE,-1, &res, &tail);
            error = sqlite3_bind_text(res, 1,file,strlen(file), SQLITE_STATIC);   assert(error == SQLITE_OK);
            if (error != SQLITE_OK) {
            handle_error("No matching record found.");

and results are parsed

    while (sqlite3_step(res) == SQLITE_ROW) 
                //do something here with results for device X

Now I would like to re-use the output ‘res’ for example, the code flow will be like

    while (sqlite3_step(res) == SQLITE_ROW) 
                //do something here with results for device X


    //reset the cursor to starting position and scan through the records.

    while (sqlite3_step(res) == SQLITE_ROW) 
                //do something here with results for device Y

How to achieve this ? I prefer not to re-run the same sql statement for the second time and fetch the results.

Answer 1

You must either cache the data yourself, or re-run the query.

Read about the reasons on this page about Sqlite and Scrolling Cursors, including:

The problem is that the sqlite3_step() function does not step through a precomputed result set at all. A better and more realistic way to think about matters is to suppose that each prepared statement is really a computer program. You are running this program in a debugger and there is a breakpoint set on a single statement somewhere deep down inside the computation. Calling the sqlite3_step() function is like pressing the “Run” button in your debugger and thus asking the debugger to run the program until it either exits or hits the breakpoint. Sqlite3_step() returns SQLITE_ROW if it hits the breakpoint and SQLITE_DONE if it finishes. If you hit the breakpoint, you can then look at local variable in order to find the values of a “row”. Then you can press the “Run” button (call sqlite3_step()) again to continue execution until the next breakpoint or until the program exits.