Sams Teach Yourself C++ in 21 Days

Exploiting References 283

9

On lines 7–17,SimpleCatis declared. On line 29, a reference to a SimpleCatis

initialized with the results of calling TheFunction(), which is declared on line

25 to return a reference to a SimpleCat.

The body of TheFunction()in lines 35–39 declares a local object of type SimpleCatand

initializes its age and weight. It then returns that local object by reference on line 38.

Some compilers are smart enough to catch this error and don’t let you run the program.

Others let you run the program, with unpredictable results.

When TheFunction()returns, the local object,Frisky, is destroyed (painlessly, I assure

you). The reference returned by this function is an alias to a nonexistent object, and this

is a bad thing.

Returning a Reference to an Object on the Heap ..........................................

You might be tempted to solve the problem in Listing 9.13 by having TheFunction()

create Friskyon the heap. That way, when you return from TheFunction(),Friskystill

exists.

The problem with this approach is: What do you do with the memory allocated for

Friskywhen you are done with it? Listing 9.14 illustrates this problem.

LISTING9.14 Memory Leaks

1: // Listing 9.14 - Resolving memory leaks

2:

3: #include <iostream>

4:

5: class SimpleCat

6: {

7: public:

8: SimpleCat (int age, int weight);

9: ~SimpleCat() {}

10: int GetAge() { return itsAge; }

11: int GetWeight() { return itsWeight; }

12:

13: private:

14: int itsAge;

15: int itsWeight;

16: };

17:

18: SimpleCat::SimpleCat(int age, int weight)

19: {

20: itsAge = age;

21: itsWeight = weight;

22: }

23:

ANALYSIS