C++ for Scientists - Technische Universität Dresden

78 CHAPTER 3. CLASSES
This mechanism applies recursively. For instance, if type1 is itself a class with an automatically
generated default constructor the default constructors of its members are called in the order
of their definition. Of those variables or some of them are also classes then their default
constructors are called and so forth. If the type of a member variable is an intrinsic type like int
or float then there are evidently no such operators because the types are no classes. However,
the behavior can be easily emulated: the “default constructor” just creates it with a random
value (whatever bits where set on the according memory position before determine its value),
the “copy constructor” and the “copy assignment” copy the values and the “destructor” does
nothing.
3.7 Accessing object members
3.7.1 Access functions
In § 3.2.2 we introduced getters and setters to access the variables of the class complex. This
becomes cumbersome when we want for instance increment the real part:
c.set r(c.get r() + 5.);
This does not really look like numeric operations and is not very readable either. A better way
dealing with this is writing a member function that returns a reference:
class complex { public:
double& real() { return r; }
};
With this function we can write:
c.real()+= 5.;
This looks already much better but still a little bit weird. Why not incrementing like this:
real(c)+= 5.;
To do this, we write a free function:
inline double& real(complex& c) { return c.r; }
But this function access the private member ‘r’. We can modify the free function calling the
member function:
inline double& real(complex& c) { return c.real(); }
Or alternatively declaring the free function as friend of complex:
class complex { public:
friend double& real(complex& c);
};
Functions or classes that are friends can access private and protected data. A strange issue
with this free function is that the inline attribute must be written before the reference type.
Usually it does not matter whether the inline is written before or after the return type. 9
9 TODO: Anybody a decent explanation for this?