BOOL writeRecord(cdbfapiPlus* handle, int recno);

Function writeRecord() writes a record from internal memory block to the file.
You have to fill the memory with necessary values using setField()

{
    // your code
    for( row = 0; row < recCount(dbf)-1; row++ )
    {
        readRecord(dbf, row);
        // change data
        writeRecord(dbf, row);
    }
}