Question

Sorry if this is a stupid question, but it’s something that I’m curious about.

I am overloading the less-than operator for my sort algorithm based on last name, first name, middle name. I realize there is not a right or wrong here, but I’m curious as to which style is written better or preferred among fellow programmers.

bool CPerson::operator<(const CPerson& key) const
{
    if (m_Last < key.m_Last)
        || ( (m_Last == key.m_Last) && (m_First < key.m_First) )
        || ( (m_Last == key.m_Last) && (m_First == key.m_First) && (m_Middle < key.m_Middle) )
        return true;
    return false;
}

or

bool CPerson::operator<(const CPerson& key) const
{
    if (m_Last < key.m_Last)
        return true;
    else if ( (m_Last == key.m_Last) && (m_First < key.m_First) )
        return true;
    else if ( (m_Last == key.m_Last) && (m_First == key.m_First) && (m_Middle < key.m_Middle) )
        return true;
    else
        return false;
}

or

bool CPerson::operator<(const CPerson& key) const
{
    if (m_Last < key.m_Last)
        return true;

    if (m_Last == key.m_Last)
        if (m_First < key.m_First)
            return true;

    if (m_Last == key.m_Last)
        if (m_First == key.m_First)
            if (m_Middle < key.m_Middle)
                return true;

    return false;
}

Answer 1

I prefer:

bool CPerson::operator<(const CPerson& key) const
{
    if (m_Last == key.m_Last) {
        if (m_First == key.m_First) {
            return m_Middle < key.m_Middle;
        }
        return m_First < key.m_First;
    }
    return m_Last < key.mLast;
}

Nice and systematic, and it is obvious how new members can be added.

---

Because these are strings, the repeated comparison may be needlessly inefficient. Following David Hamman’s suggestion, here is a version which only does the comparisons once per string (at most):

bool CPerson::operator<(const CPerson& key) const
{
    int last(m_Last.compare(key.m_Last));
    if (last == 0) {
        int first(m_First.compare(key.m_First));
        if (first == 0) {
            return m_Middle < key.m_Middle;
        }
        return first < 0;
    }
    return last < 0;
}