SQLite returning NULL rows

Question

I'm having trouble selecting and displaying a table from my database. I'm getting the correct number of rows from my query but all of them are SQLite NULL values (0 or 0.0). Everything runs fine if I use the same query in SQLiteStudio. I'm probably doing something obviously wrong but I don't know what.

    sqlite3 *db;
    char *zErrMsg = 0;

    char const* const command = "Select * FROM Location";

    sqlite3_open("DB.db3", &db);

    sqlite3_stmt *stmt = NULL;
    string t;
    int rc = sqlite3_prepare_v2(db, command, -1, &stmt, NULL);
    int row_counter = 0;

    while (1) {
    row_counter++;
        int rc = sqlite3_step(stmt);
        if (rc == SQLITE_DONE)
            break;
        if (rc != SQLITE_ROW) {
            break;
        }
    }

    for (int i = 0; i < row_counter; i += 4)
    {
        t += "LocationID = " + to_string(sqlite3_column_int(stmt, i)) + "\n" +
            "PositionX = " + to_string(sqlite3_column_double(stmt, i + 1)) + "\n" +
            "PositionY = " + to_string(sqlite3_column_double(stmt, i + 2)) + "\n" +
            "PositionZ = " + to_string(sqlite3_column_double(stmt, i + 3)) + "\n";
    }

    WriteToFile(t, "query_result.txt");
    sqlite3_finalize(stmt);

Here's the query_result.txt

LocationID = 0
PositionX = 0.000000
PositionY = 0.000000
PositionZ = 0.000000
LocationID = 0
PositionX = 0.000000
PositionY = 0.000000
PositionZ = 0.000000
LocationID = 0
PositionX = 0.000000
PositionY = 0.000000
PositionZ = 0.000000

Wayne Tanner · Accepted Answer · 2015-12-15 17:16:59Z

2

I think you need to access the column values inside of the if statement for SQLITE_ROW. At the point you're trying to get the column values, the result set has already been iterated and stmt no longer points to a valid row. See the changes I made below for an example of what I'm talking about. This assumes the values are in columns 0 to 3.

    while (1) {
row_counter++;
    int rc = sqlite3_step(stmt);
    if (rc == SQLITE_DONE)
        break;
    if (rc == SQLITE_ROW) {
          t += "LocationID = " + to_string(sqlite3_column_int(stmt, 0)) + "\n" +
            "PositionX = " + to_string(sqlite3_column_double(stmt, 1)) + "\n" +
            "PositionY = " + to_string(sqlite3_column_double(stmt, 2)) + "\n" +
            "PositionZ = " + to_string(sqlite3_column_double(stmt, 3)) + "\n";
    }
}

answered Dec 15, 2015 at 17:16

Wayne Tanner

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