C++ for Scientists - Technische Universität Dresden

2.11. REAL-WORLD EXAMPLE: MATRIX INVERSION 53
Feature Pointers References
Referring defined location - +
Mandatory initialisation - +
Avoidance of memory leaks - +
Object-like notation - +
Memory management + -
Adress calculation + -
Table 2.2: comparison between pointers and references
For short, references are not idiot-proof but much less error-prone than pointers. Pointers
should be only used when dealing with dynamic memory and even then one should do this via
well-tested types or encapsulate the pointer within a class.
2.10.4 Do Not Refer Outdated Data
Variables in functions are only valid within this function, for instance:
double& square ref(double d) // DO NOT!
{
double s= d ∗ d;
return s;
}
The variable s is not valid anymore after the function is finished. If you are lucky the memory
where s was stored is not overwritten yet. But this is nothing one can count on. Good compilers
will warn you that you are referring local variable. Sadly enough we have seen examples in web
tutorial that do this!
The same applies correspondingly to pointers:
double∗ square ptr(double d) // DO NOT!
{
double s= d ∗ d;
return &s;
}
This is as wrong as it is for references.
There are cases where functions, esp. member functions return references and addresses and
the destruction order of object impedes the invalidation of references, 24 cf. § ??.
2.11 Real-world example: matrix inversion
TODO: I am not sure anymore if this is very good here. I still think we should propagate
abstraction and demonstrate how to develop reusable software but the section feels now a bit
misplaced. At the beginning of the next chapter is not much better. Maybe a good intro
paragraph saves the situation.
24 Unfortunately there are ways to circumvent this and an exception to this rule.