1. Pointers and Dynamic Arrays

2. Pointers and Dynamic Memory
Pointer: is the memory address of a variable
Memory address: at byte level
Example:
The integer i is located at
memory address 990.

3. Pointer Variables Syntax Examples Type_Name *var_name; int *cursor;
char *c1_ptr, *c2_ptr;

4. Address Operator Examples Dereferencing operator int *example_ptr;
int i;
Example_ptr = &i; //the address of i is put into the pointer variable example_ptr
Dereferencing operator
i = 42;
example_ptr = &i;
cout << i << endl;
cout << *example_ptr << endl;

5. More Example int *example_ptr; int i; i = 42; example_ptr = &i;
cout << i << endl;
cout << *example_ptr << endl;

6. Pointer Assignment int i = 42; int *p1; int *p2; p1 = &i; p2 = p1;
cout << *p1 << endl;
cout << *p2 << endl;

7. Pointer Assignment int i = 42; int j = 80; int *p1; int *p2; p1 = &i;
p2 = &j;
*p2 = *p1;
cout << *p1 << endl;
cout << *p2 << endl;

9. NULL Pointer NULL – constant defined in cstdlib
Means pointing to nothing

10. Dynamic Variables Not declared Created during execution of a program
Memory is allocated using an new operator in a special memory location called the heap
Examples:
int *n;
n = new int;
*n = 5;
// Can be combined in 1 statement
int *n = new int(5);

11. Dynamic Arrays Dynamically allocate entire array int *a = new int[20];
Returns a pointer to the first element in the array

13. Failure of new Operator
new operator fails if insufficient memory is available in the heap
bad_alloc exception is thrown

14. Delete Operator
When dynamic variable is no longer needed – need to release its memory
delete operator
Example
int *n = new int(5); ……
delete n;
double* a = new double[6];
delete [] a;

15. Define Pointer Types Example typedef int* int_pointer;
int_pointer i_ptr;

16. Pointers as Parameters
Passing pointers as value parameters
Pointer cannot be changed – object pointed to can be changed
Example
void confuz (int* n) {
*n = 2; }

17. Arrays as Parameters
Array name is treated as a pointer to first element in array
Size of array is not passed in as part of the array – must be done separately
Example:
void make_it_all_42(int a[], size_t n) {
for (size_t i = 0; i < n; i++)
a[i] = 42; }
int *numbers = new int[10];
make_it_all_42(numbers, 10);

18. const Parameters void confuz (const int* n);
Integer being pointed to by n cannot be modified
void confuz (const int a[], size_t n);
No element of array a can be modified

19. Pointer Reference Parameters
Pointer parameter can be modified since passed by reference
Example:
void confuz (int*& n) {
n = new int (5); }

20. Dynamic Bag Implementing the bag class with a dynamic array private:
value_type *data;
size_type used;
size_type capacity;

21. Copy Constructor
A copy constructor is a constructor with exactly one argument, and the data type of the argument is the same as the constructor’s class
Need to make sure that the object and its copy are independent from each other (deep copy)
For member data that are pointers – copy objects being pointed to (recursively)
Shallow copy – only copy pointers
bag(const bag& source);
bag y(x); //initialize y as a copy of x

22. Overloading Assignment Operator
Need to use same copying concept as with copy constructors
void operator =(const bag& source);
bag y = x; //initialize y as a copy of x

23. Destructor Deallocate object's dynamic memory
Name – class name preceded by ~
No parameters & no return type
Automatically called when object is destroyed
bag::~bag( ) {
delete [ ] data; }

24. Dynamic Class Design Some of the member data are pointers
Some member functions allocate & deallocate dynamic memory
Assignment operator needs to be overloaded
Copy constructor must be constructed
Destructor must be constructed

25. C strings Null character (‘\0’) terminated arrays of characters
char s[n] – can hold at most n-1 characters
Empty string char quiet[20]=“”;
strcpy
strcmp
strcat
strlen

26. STL string class Added in later versions of C++
Designed to address weaknesses of C version