- (void) clearRecord;

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 asString:@"some value" asDouble:0];
    [dbf setField:1 asString:nil asDouble:123.45];
    [dbf appendRecord:NO];
    // your code
}