The function clearRecord() removes all data from internal memory and fills it with zeroes (0x00) or spaces (0x20).
You can call this function before calling setField(), setMemoBuf().
{
// your code
dbf->clearRecord();
dbf->setField(0, "some value", 0);
dbf->setField(1, NULL, 123.45);
dbf->appendRecord(FALSE);
// your code
}