Recap: Pointers. int* int& *p &i &*&* ** * * * * IFMP 18, M. Schwerhoff

Transcription

1 Recap: Pointers IFMP 18, M. Schwerhoff int* int& *p &i &*&* ** * * * *

2 A 0 A 1 A 2 A 3 A 4 A 5

3 A 0 A 1 A 2 A 3 A 4 A 5 5 i

4 int* p; A 0 A 1 A 2 A 3 A 4 A 5 5 i p

5 int* p; p = &i; A 0 A 1 A 2 A 3 A 4 A 5 5 A 0 i p

6 int* p; p = &i; A 0 A 1 A 2 A 3 A 4 A A 0 *p = 7; i p

7 int* p; p = &i; A 0 A 1 A 2 A 3 A 4 A 5 7 A 0 *p = 7; cout << i; // 7 i p

8 int* p; p = &i; *p = 7; cout << i; // 7 int j = *p + 1; A 0 A 1 A 2 A 3 A 4 A 5 7 A 0 8 i p j

9 int* p; p = &i; *p = 7; cout << i; // 7 int j = *p + 1; p = &j; A 0 A 1 A 2 A 3 A 4 A 5 7 A 04 8 i p j

10 int* p; p = &i; *p = 7; cout << i; // 7 int j = *p + 1; p = &j; cout << *p; // 8 A 0 A 1 A 2 A 3 A 4 A 5 7 A 4 8 i p j

11 int* p; p = &i; *p = 7; cout << i; // 7 int j = *p + 1; p = &j; cout << *p; // 8 (*p)++; A 0 A 1 A 2 A 3 A 4 A 5 7 A i p j

12 int* p; p = &i; *p = 7; cout << i; // 7 int j = *p + 1; p = &j; cout << *p; // 8 (*p)++; p++; A 0 A 1 A 2 A 3 A 4 A 5 7 A 45 9 i p j

13 int* p = &i; A 0 A 1 A 2 A 3 A 4 A 5 5 A 0 i p

14 int* p = &i; A 0 A 1 A 2 A 3 A 4 A 5 cout << p; // A 0 5 A 0 i p

15 int* p = &i; A 0 A 1 A 2 A 3 A 4 A 5 cout << p; // A 0 5 A 0 cout << *p;// 5 i p

16 int* p = &i; A 0 A 1 A 2 A 3 A 4 A 5 cout << p; // A 0 5 A 0 cout << *p;// 5 cout << &p;// A 2 i p

17 Recap: Pointers vs. References

18 Pointers vs. References int* p = &i; int& r = i; Declaration and initialisation

19 Pointers vs. References int* p = &i; int& r = i; *p = 0; // i = 0 r = 0; // i = 0 Declaration and initialisation Writing to underlying variable

20 Pointers vs. References int* p = &i; int& r = i; *p = 0; // i = 0 r = 0; // i = 0 cout << *p; // 0 cout << r; // 0 Declaration and initialisation Writing to underlying variable Reading underlying variable

21 Pointers vs. References int* p = &i; int& r = i; *p = 0; // i = 0 r = 0; // i = 0 cout << *p; // 0 cout << r; // 0 Declaration and initialisation Writing to underlying variable Reading underlying variable int* p; int& r; p = &i; r = i; References must be initialised immediately

22 Pointers vs. References int* p = &i; int& r = i; *p = 0; // i = 0 r = 0; // i = 0 cout << *p; // 0 cout << r; // 0 Declaration and initialisation Writing to underlying variable Reading underlying variable int* p; int& r; p = &i; r = i; References must be initialised immediately int* p = &i; int& r = i; p = &j; r = j; References themselves cannot be changed ( redirected )

23 Pointers vs. References int* p = &i; int& r = i; *p = 0; // i = 0 r = 0; // i = 0 cout << *p; // 0 cout << r; // 0 Declaration and initialisation Writing to underlying variable Reading underlying variable int* p; int& r; p = &i; r = i; References must be initialised immediately int* p = &i; int& r = i; p = &j; r = j; References themselves cannot be changed (are always const) int* p = &i; int& r = i; cout << &p; cout << &r; References don t have addresses (they are just aliases of sth. else)

24 Why Pointers and References?

25 Why Pointers and References? Historical language development: C: 1969; has pointers C++: 1983 Inherited pointers from C (backwards compatibility) Added references to support operator overloading

26 Why Pointers and References? Historical language development: C: 1969; has pointers C++: 1983 Inherited pointers from C (backwards compatibility) Added references to support operator overloading Rule of thumb: prefer references over pointers, if possible References are more restricted harder to make mistakes Reference syntax is nicer (r vs *p) easier to read

27 Why Pointers and References? When do we need pointers? Dynamic memory allocation (new) Fast(er) iteration over data: e.g. arrays (last week) and containers (today)

28 Why Pointers and References? When do we need pointers? Dynamic memory allocation (new) Fast(er) iteration over data: e.g. arrays (last week) and containers (today) Dynamic data structures that change over time, such as lists, trees or graphs B B A C D A C D E F E F