void setOrder(char* fieldlist);

Function setOrder() sets order of records by some field or list of fields.
The function does not change a file, it re-orders records in a memory.
One function accepts a string with fields delimited by comma, another function accepts an array.
To return the original order of records - call unserOrder().
function descendingMode() set either ascending or descending order.

void setOrderA(char* fields[]);
void unsetOrder();
void descendingMode(BOOL descending);

    // your code
    dbf->setOrderA( {"FIRSTNAME", "LASTNAME"} );
    // your code