Chapter 7 Pointers :

1. Chapter 7 Pointers: • Java does not have pointers. • Used for dynamic memory allocation.

2. Example: Employee* boss // does not create the object! boss = new Employee or boss = new Employee(parameters); • boss is a pointer to the object. • *boss is the object. • (*boss).method() or bossmethod() is the proper way to access a method.

3. Note the syntax and common errors on p. 309-10. • In a method, this is a pointer to the implicit parameter (object specified when the method was called). Key word this is not necessary but some like it.

4. Function new • boss = New Employee() • allocates memory from the heap for the object itself. • Variable boss is allocated on the stack.

5. HEAP ALLOCATED MEMORY MUST BE DISPOSED OF WHEN IT IS NO LONGER USED. • Use deleteboss at some point. • Java has automatic garbage collection C++ does NOT. • If not used, the result can be a memory leak (unusable memory).

6. dangling pointers: • A pointer that has not been initialized or a pointer after the associated heap memory is deleted. • COMMON ERROR is to try to access a dangling pointer. • Do example from the snippets file.

7. Address operator: • If x is a pointer and y is an object then we can write x=&y. • In this case, *x and y are the same thing. x y

8. Do example from the snippets file under Pointers. Try a few things: • Set x to y. • Reference *x after deleting it. • Set x to y and delete y. Set x to y and delete both x and y. • Try deleting p. • Examine all in the watch window. • Display q[0] toward the end of the main.

9. Set up tempdemo for department.cpp. Code on p. 317. • Shows why pointers are useful • What happens if you write delete tina prior to qc.print() in the main program? • Note the comparison between a reference parameter and specifying a pointer as a parameter. p. 319. Important!

10. Discuss common errors on p. 329. • Demo04: listing of accounts for a customer is done by going through ALL account objects. • This is NOT a good design. • Demo06 uses an array of pointers inside the customer class to locate a list of account objects.

11. Arrays and pointers: • int a[10] similar to int* a and a = new int[10] • Could also use a = new int[n], where n is input by the user. • a[i] same as *(a+i) • This is a dynamic array in contrast to a static array discussed previously.

12. Example int a=99; int * x; int b=99; x = new int[5]; for (inti=0; i<5; i++) *(x+i)=i*i; for (inti=0; i<5; i++) cout << x[i] << " "; cout << endl; cout << "a is " << a << " b is " << b << endl; cout << endl;

13. See advance topic on p. 323 • See Quality Tip on p. 324 • COMP SCI 370 may cover this in more detail. • See common error 7.6 on p. 325 and demo the code as written in the notes. • See advanced topic on p. 326.

14. Do, also, 2D dynamic arrays. In particular look at code from the snippet file (optional) • While running this program take a look at the debugger. In particular put m, m[0], m[1], etc in a watch window. Also, while running, take a look at the memory window to see the actual contents of memory.

15. Pointers to character strings: • Explain the difference between char c = ‘A’ and char* c = “A”. This is a COMMON problem in C. • Explain problem with comparing char* p and char * q with p == q using this example

16. #include <iostream> using namespace std; int main( ) { char* x = "Harry"; char * y; y=new char[6]; strcpy(y, "Harry"); cout << "x is " << x << " y is " << y << endl; if (x == y) cout << "strings are equal"; else cout<< "string are NOT equal"; return 0; }