C pointers
Download
1 / 16

C++ Pointers - PowerPoint PPT Presentation


  • 345 Views
  • Updated On :
  • Presentation posted in: Funny / Jokes

C++ Pointers. Gordon College. 27. Regular variables. Regular variables declared Memory allocated for value of specified type Variable name associated with that memory location Memory initialized with values provided (if any). Pointers. Pointer Variables contains a memory address

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha

Download Presentation

C++ Pointers

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


C++ Pointers

Gordon College


27

Regular variables

  • Regular variables declared

    • Memory allocated for value of specified type

    • Variable name associated with that memory location

    • Memory initialized with values provided (if any)


Pointers

  • Pointer Variables

    • contains a memory address

    • pointer variable should be typed int *Ptr

      • However could be a void pointer void *Vptr

    • two operators:

      • Dereference *

      • Address of&


Basic Pointer Operations

  • Dereferencing and indirection

    • Pointer variable stores address of a location

    • Accessing contents of that location requires dereferencing operator *

      cout << *iPtr;

Dereferencing pointer

int *iPtr = &i;

Pointer declaration

PointerFun Video


Basic Pointer Operations

  • Assignment

    • Pointer variables can be assigned the values of other pointer variables bound to same type

int *iPtr = &i;

int *jPtr = &j;

jPtr = iPtr;


Basic Pointer Operations

  • Consider: *jPtr = 44;

    • Changes value that both pointers reference

    • Not good programming practice, hard to debug

    • Known as aliasing problem


Basic Pointer Operations

  • Comparison

    • Relational operators used to compare two pointers

    • Must be bound to same type

    • Most common == and !=

    • The null address may be compared with any pointer variable

int* t;

double *d;

if (t == d)

ERROR

Fix:

if (t == (int*) d)


Initial value for pointers

  • Variables are not automatically given an initial value by the system - they start with whatever garbage is left in memory when they are allocated.

    #include <cstdlib>

    . . .

    Node* head = NULL; // Initialized pointer to NULL.

WARNING: Invalid addresses in pointer can cause problems -

known as “wild pointers” when not initialized


Pointers vs. References

  • Consider this code:

    int i; int i;

    int *p = &i; int &r = i;

    *p = 5; r = 5;

Both p and r contain addresses which point to the variable i, however

these “addressing” variables are used differently in code.

Why bother with pointers?


Pointers vs. References

  • Pointer arithmetic

    i.e. p++p-- ptr = sptr + 1;

char* GetFirstT(char* p)

{

for ( ; *p ; ++p)

{

if ( *p == 't' ) return p;

}

return 0;

}

signedmain()

{

char the_alphabet[] = "abcdefghijklmnopqrstuvwxyz";

char* p_t = GetFirstT(the_alphabet);

cout << p_t - the_alphabet << endl;

}

OUTPUT: 19


Dynamic Memory Allocation

  • The new operation

  • Exampleint * intPtr;intPtr = new int;

    • An anonymous variable

    • Cannot be accessed directly

    • Warning: watch out for memory leak


Memory Management Problems

  • Memory leak - program fails to release memory when no longer needed

    {

    int *t = newint(4);

    }

    Solution: must use the delete command before existing block

  • Dangling Pointer - an object is deleted or deallocated, without modifying the value of the pointer.

    char *cp = NULL;

    {

    char c;

    cp = &c;

    }Solution: set pointer to NULL before exiting block


Pointer Arguments

  • Pointers can be passed as arguments to functions

  • This is logically equivalent to reference parameters

    • In fact, this is how early C++ compilers accomplished reference parameters


Pointer to a Pointer

int cow(7);

int* p_cow = &cow;

int** p_p_cow(&p_cow);

int*** p_p_p_cow = &p_p_cow;

Name of VariableType of VariableAddress in MemoryValue Stored

Cow Int 108 7

p_cow int* 110108

p_p_cow int** 112 110

p_p_p_cow int*** 114 112

int cow(7);

int* p_cow = &cow;

int** p_p_cow(&p_cow);

int*** p_p_p_cow = &p_p_cow;

***p_p_p_cow = 8;


Pointer to objects

  • Declaration:

    classType *name = &object

  • Accessing the object:

    (*name).method();

    name->method();


Pointers to objects (from lab2)

Pet * kennel[10];// The cages in the kennel

char dashes[] = "----------------------------------------";

kennel[0] = new Rodent("Mickey", "W. Disney", "01/01/2002", "01/04/2002","mouse");

kennel[1] = new Bird("Tweety", "Granny", "9.1.2001", "9/5/2001","canary");

kennel[2] = new Reptile("Ignatius", "B. Starr", "10/07/2001", "10/10/2001","iguana");

kennel[3] = new Cat("Garfield", "J. Arbuckle", "01/01/2002", "01/31/2002",20, true);

kennel[4] = new Dog("Snoopy", "C. Brown", "01/01/2002", "01/02/2002",15, false, "beagle");

kennel[5] = new Cat("Sylvester", "Granny", "09/01/2001", "09/05/2001",15, false);

kennel[6] = new Dog("Butch", "Granny", "09/01/2001", "09/05/2001",45, true, "bulldog");

kennel[9] = kennel[8] = kennel[7] = NULL;

for (int i = 0; i < 10 && kennel[i] != NULL; i++)

{

cout << endl << dashes << dashes << endl << endl;

cout << "Bill for: " << kennel[i] -> getName() << endl << endl;

kennel[i] -> printBill();

cout << endl << dashes << dashes << endl;

}


ad
  • Login