void setField(int fieldno, char* string, double value);

Function setField() puts values to a field in memory before writing a record to a disc.
There are different versions of setField: you can pass a double value, a string or both. In last case setField will use a value which is more suitable for this type of field.

{
    dbf.clearRecord();
    dbf.setField(0, "string value");
    dbf.setField(1, 123.45);
    dbf.setField(2, "the string", 666.66);
    dbf.writeRecord(0);
}