Page 155 - DCAP404 _Object Oriented Programming
P. 155
Object-oriented Programming
Notes {
private:
int m_nCents;
public:
Cents(int nCents) { m_nCents = nCents; }
// Overload -cCents
friend Cents operator-(const Cents &cCents);
};
// note: this function is not a member function!
Cents operator-(const Cents &cCents)
{
return Cents(-cCents.m_nCents);
}
Now let’s overload the same operator using a member function instead:
class Cents
{
private:
int m_nCents;
public:
Cents(int nCents) { m_nCents = nCents; }
// Overload -cCents
Cents operator-();
};
// note: this function is a member function!
Cents Cents::operator-()
{
return Cents(-m_nCents);
}
You’ll note that this method is pretty similar. However, the member function version of operator-
doesn’t take any parameters! Where did the parameter go? In the lesson on the hidden this
pointer, you learned that a member function has an implicit *this pointer which always points
to the class object the member function is working on. The parameter we had to list explicitly in
the friend function version (which doesn’t have a *this pointer) becomes the implicit *this
parameter in the member function version.
!
Caution Remember that when C++ sees the function prototype Cents Cents::operator-();,
the compiler internally converts this to Cents operator-(const Cents *this), which you will
note is almost identical to our friend version Cents operator-(const Cents &cCents)!
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