This document discusses pointers in C programming. It begins with an introduction to pointers and memory organization. It then covers basics of pointers including declaration, initialization, dereferencing, and pointer expressions. The document discusses various pointer applications including pointer arithmetic, pointers to pointers, dynamic memory allocation, pointers and arrays, and character strings. It provides examples to illustrate concepts like pointer expressions and pointer arithmetic with arrays. The document is intended as a reference for understanding pointers in C.

1. 1
Pointers in C
Chapter 6
By:-Gourav Kottawar

2. Contents
6.1 Introduction
6.2 Memory Organization
6.3 Basics of Pointer
6.4 Application of Pointer
6.5 Pointer Expressions
Declaration of Pointer, Initializing
Pointer,
De-referencing Pointer
Void Pointer
Pointer Arithmetic
6.6 Precedence of &, * operators
6.7 Pointer to Pointer
6.8 Constant Pointe
2
6.9 Dynamic Memory
Allocation
6.10 sizeof(), malloc(), calloc(),
realloc(), free()
6.11 Pointers and Arrays
6.12 Pointers and character
string
6.13 Array of pointers

3. 3
Pre-requisite
 Basics of the C programming language
 Data type
 Variable
 Array
 Function call
 Standard Input/Output
 e.g. printf(), scanf()

4. Pointers - Introduction
 Pointer is a derived type.
 Pointers contain memory address as
their values.
 Pointers can be used to access and
manipulate data stored in memory.
4

5. 5
Computer Memory Revisited
 Computers store data in memory slots
 Each slot has an unique address
 Variables store their values like this:
Addr Content Addr Content Addr Content Addr Content
1000 i: 37 1001 j: 46 1002 k: 58 1003 m: 74
1004 a[0]: ‘a’ 1005 a[1]: ‘b’ 1006 a[2]: ‘c’ 1007 a[3]: ‘0’
1008 ptr: 1001 1009 … 1010 1011

6. 6
Computer Memory Revisited
 Altering the value of a variable is indeed
changing the content of the memory
 e.g. i = 40; a[2] = ‘z’;
Addr Content Addr Content Addr Content Addr Content
1000 i: 40 1001 j: 46 1002 k: 58 1003 m: 74
1004 a[0]: ‘a’ 1005 a[1]: ‘b’ 1006 a[2]: ‘z’ 1007 a[3]: ‘0’
1008 ptr: 1001 1009 … 1010 1011

7. 7
Addressing Concept
 Pointer stores the address of another
entity
 It refers to a memory location
int i = 5;
int *ptr; /* declare a pointer variable */
ptr = &i; /* store address-of i to ptr */
printf(“*ptr = %dn”, *ptr); /* refer to referee of ptr */

8. 8
Why do we need Pointer?
 Simply because it’s there!
 It is used in some circumstances in C
Remember this?
scanf(“%d”, &i);

9. Benefits of pointers
 More efficient in handling arrays and data
tables.
 Pointers can be used to return multiple values
from a function via function arguments.
 Pointers permit references to functions and
there by facilitating passing of functions as
arguments to other functions.
 The use of pointer arrays to character strings
result in saving of data storage space in
memory. 9

10. Benefits of Pointer
 Pointers allow C to support DMA.
 Pointers provides an efficient tool for
manipulating dynamic data structures such as
structures, linked list, trees, etc.
 Pointers reduce length and complexity
program.
 They increase execution speed and thus
reduce the program execution time.
10

11. 11
What actually ptr is?
 ptr is a variable storing an address
 ptr is NOT storing the actual value of i
int i = 5;
int *ptr;
ptr = &i;
printf(“i = %dn”, i);
printf(“*ptr = %dn”, *ptr);
printf(“ptr = %pn”, ptr);
5i
address of iptr
Output:
i = 5
*ptr = 5
ptr = effff5e0
value of ptr =
address of i
in memory

12. 12
Twin Operators
 &: Address-of operator
 Get the address of an entity
 e.g. ptr = &j;
Addr Content Addr Content Addr Content Addr Content
1000 i: 40 1001 j: 33 1002 k: 58 1003 m: 74
1004 ptr: 1001 1005 1006 1007

13. 13
Twin Operators
 *: De-reference operator
 Refer to the content of the referee
 e.g. *ptr = 99;
Addr Content Addr Content Addr Content Addr Content
1000 i: 40 1001 j: 99 1002 k: 58 1003 m: 74
1004 ptr: 1001 1005 1006 1007

14. example
 Write a program to print address of
variable along with value.
14

15. Declaring pointer variables
 Syntax
data_type *pt_name
 Ex-
int* ptr;
int *ptr;
int * ptr;
15

16. Initialization of pointer variables
 ptr= &a;
16

17. So,
 Pointer is a variable just like other
variables of c but only difference is
unlike the other variable it stores the
memory address of any other variables
of c. This variable may be type
of int, char, array, structure, function or
any other pointers.
 Examples
17

18. 18
 (1)
Pointer p which is storing memory address of a int type variable:
int i=50;
int *p=&i;
 (2)
Pointer p which is storing memory address of an array:
int arr[20];
int (*p)[20]=&arr;
 (3)
Pointer p which is storing memory address of a function:
char display(void);
char(*p)(void)=&display;

19. 19
(4)
Pointer p which is storing memory address of struct type
variable:
struct abc
{
int a;
float b;
}var;
struct abc *p=&var;

20. 20
Example: Pass by Reference
 Modify behaviour in argument passing
void f(int j)
{
j = 5;
}
void g()
{
int i = 3;
f(i);
}
void f(int *ptr)
{
*ptr = 5;
}
void g()
{
int i = 3;
f(&i);
} i = ?i = ?i = 3 i = 5

21. 21
An Illustration
int i = 5, j = 10;
int *ptr;
int **pptr;
ptr = &i;
pptr = &ptr;
*ptr = 3;
**pptr = 7;
ptr = &j;
**pptr = 9;
*pptr = &i;
*ptr = -2;
Data Table
Name Type Description Value
i int integer variable 5
j int integer variable 10

22. 22
An Illustration
int i = 5, j = 10;
int *ptr; /* declare a pointer-to-integer variable */
int **pptr;
ptr = &i;
pptr = &ptr;
*ptr = 3;
**pptr = 7;
ptr = &j;
**pptr = 9;
*pptr = &i;
*ptr = -2;
Data Table
Name Type Description Value
i int integer variable 5
j int integer variable 10
ptr int * integer pointer variable

23. 23
An Illustration
int i = 5, j = 10;
int *ptr;
int **pptr; /* declare a pointer-to-pointer-to-integer variable */
ptr = &i;
pptr = &ptr;
*ptr = 3;
**pptr = 7;
ptr = &j;
**pptr = 9;
*pptr = &i;
*ptr = -2;
Data Table
Name Type Description Value
i int integer variable 5
j int integer variable 10
ptr int * integer pointer variable
pptr int ** integer pointer pointer variable
Double Indirection

24. 24
An Illustration
int i = 5, j = 10;
int *ptr;
int **pptr;
ptr = &i; /* store address-of i to ptr */
pptr = &ptr;
*ptr = 3;
**pptr = 7;
ptr = &j;
**pptr = 9;
*pptr = &i;
*ptr = -2;
Data Table
Name Type Description Value
i int integer variable 5
j int integer variable 10
ptr int * integer pointer variable address of i
pptr int ** integer pointer pointer variable
*ptr int de-reference of ptr 5

25. 25
An Illustration
int i = 5, j = 10;
int *ptr;
int **pptr;
ptr = &i;
pptr = &ptr; /* store address-of ptr to pptr */
*ptr = 3;
**pptr = 7;
ptr = &j;
**pptr = 9;
*pptr = &i;
*ptr = -2;
Data Table
Name Type Description Value
i int integer variable 5
j int integer variable 10
ptr int * integer pointer variable address of i
pptr int ** integer pointer pointer variable address of ptr
*pptr int * de-reference of pptr value of ptr
(address of i)

26. 26
An Illustration
int i = 5, j = 10;
int *ptr;
int **pptr;
ptr = &i;
pptr = &ptr;
*ptr = 3;
**pptr = 7;
ptr = &j;
**pptr = 9;
*pptr = &i;
*ptr = -2;
Data Table
Name Type Description Value
i int integer variable 3
j int integer variable 10
ptr int * integer pointer variable address of i
pptr int ** integer pointer pointer variable address of ptr
*ptr int de-reference of ptr 3

27. 27
An Illustration
int i = 5, j = 10;
int *ptr;
int **pptr;
ptr = &i;
pptr = &ptr;
*ptr = 3;
**pptr = 7;
ptr = &j;
**pptr = 9;
*pptr = &i;
*ptr = -2;
Data Table
Name Type Description Value
i int integer variable 7
j int integer variable 10
ptr int * integer pointer variable address of i
pptr int ** integer pointer pointer variable address of ptr
**pptr int de-reference of de-reference of
pptr
7

28. 28
An Illustration
int i = 5, j = 10;
int *ptr;
int **pptr;
ptr = &i;
pptr = &ptr;
*ptr = 3;
**pptr = 7;
ptr = &j;
**pptr = 9;
*pptr = &i;
*ptr = -2;
Data Table
Name Type Description Value
i int integer variable 7
j int integer variable 10
ptr int * integer pointer variable address of j
pptr int ** integer pointer pointer variable address of ptr
*ptr int de-reference of ptr 10

29. 29
An Illustration
int i = 5, j = 10;
int *ptr;
int **pptr;
ptr = &i;
pptr = &ptr;
*ptr = 3;
**pptr = 7;
ptr = &j;
**pptr = 9;
*pptr = &i;
*ptr = -2;
Data Table
Name Type Description Value
i int integer variable 7
j int integer variable 9
ptr int * integer pointer variable address of j
pptr int ** integer pointer pointer variable address of ptr
**pptr int de-reference of de-reference of
pptr
9

30. 30
An Illustration
int i = 5, j = 10;
int *ptr;
int **pptr;
ptr = &i;
pptr = &ptr;
*ptr = 3;
**pptr = 7;
ptr = &j;
**pptr = 9;
*pptr = &i;
*ptr = -2;
Data Table
Name Type Description Value
i int integer variable 7
j int integer variable 9
ptr int * integer pointer variable address of i
pptr int ** integer pointer pointer variable address of ptr
*pptr int * de-reference of pptr value of ptr
(address of i)

31. 31
An Illustration
int i = 5, j = 10;
int *ptr;
int **pptr;
ptr = &i;
pptr = &ptr;
*ptr = 3;
**pptr = 7;
ptr = &j;
**pptr = 9;
*pptr = &i;
*ptr = -2;
Data Table
Name Type Description Value
i int integer variable -2
j int integer variable 9
ptr int * integer pointer variable address of i
pptr int ** integer pointer pointer variable address of ptr
*ptr int de-reference of ptr -2

32. Chain of pointers
32
Address
2
Address 1 value
P2 p1 variable
The pointer variable p2 contains the address of the pointer
variable p1 which points to the location that contains the
desired value. This is known as multiple indirection.
•Example

33. Pointer Expression
Y = *p1 * *p2;
Sum=sum + *p1;
Z=5* - *p2/ *p1;
*p2= *p2+10;
P1 + 4;
P1 -2
P1-p2
33

34. example
main()
{ int a,b,*p1,*p2,x,y,z;
a=12;b=4; p1=&a;p2=&b;
x=*p1 * *p2 – 6;
y=4* - *p2 / * p1+10;
printf(“Address of a = %u”,p1);
printf(“n Address of b = %u”,p2);
printf(“a= %d, b= %d”.a,b);
printf(“x= %d , y= %d”,x,y);
*p2 = *p2 +3;
*p1= *p2 – 5;
z= *p1 * *p2 – 6;
printf(“n a = %d , b = %d”, a,b);
printf(“n z= %d”,z);
}
34

35. Pointer Increment and scale
factor
 characters 1 byte
 Integers 2 bytes
 Floats 4 bytes
 Long integers 4 bytes
 Doubles 8 bytes
35

36. Rules of pointer variable
 A pointer variable can be assigned the address of another
varaible.
 A pointer variable can be assigned the values of another
pointer variable.
 A pointer variable can be initialized with NULL or zero
value.
 A pointer variable can be pre-fixed or post-fixed with
increment or decrement operators.
 An integer value may be added or subtracted from a
pointer variable.
 When two pointers point to the same array, one pointer
variable can be subtracted from other.
 When two pointers point to the same objects of the same
data types, they can compared using relational operators.
 Two pointer variable can not be added
 A value can not be assigned to an arbitrary address. i.e x=
&10; 36

37. 37
Pointer Arithmetic
 What’s ptr + 1?
The next memory location!
 What’s ptr - 1?
The previous memory location!
 What’s ptr * 2 and ptr / 2?
Invalid operations!!!

38. 38
Pointer Arithmetic and Array
float a[4];
float *ptr;
ptr = &(a[2]);
*ptr = 3.14;
ptr++;
*ptr = 9.0;
ptr = ptr - 3;
*ptr = 6.0;
ptr += 2;
*ptr = 7.0;
Data Table
Name Type Description Value
a[0] float float array element (variable) ?
a[1] float float array element (variable) ?
a[2] float float array element (variable) ?
a[3] float float array element (variable) ?
ptr float * float pointer variable
*ptr float de-reference of float pointer
variable
?

39. 39
Pointer Arithmetic and Array
float a[4];
float *ptr;
ptr = &(a[2]);
*ptr = 3.14;
ptr++;
*ptr = 9.0;
ptr = ptr - 3;
*ptr = 6.0;
ptr += 2;
*ptr = 7.0;
Data Table
Name Type Description Value
a[0] float float array element (variable) ?
a[1] float float array element (variable) ?
a[2] float float array element (variable) ?
a[3] float float array element (variable) ?
ptr float * float pointer variable address of a[2]
*ptr float de-reference of float pointer
variable
?

40. 40
Pointer Arithmetic and Array
float a[4];
float *ptr;
ptr = &(a[2]);
*ptr = 3.14;
ptr++;
*ptr = 9.0;
ptr = ptr - 3;
*ptr = 6.0;
ptr += 2;
*ptr = 7.0;
Data Table
Name Type Description Value
a[0] float float array element (variable) ?
a[1] float float array element (variable) ?
a[2] float float array element (variable) 3.14
a[3] float float array element (variable) ?
ptr float * float pointer variable address of a[2]
*ptr float de-reference of float pointer
variable
3.14

41. 41
Pointer Arithmetic and Array
float a[4];
float *ptr;
ptr = &(a[2]);
*ptr = 3.14;
ptr++;
*ptr = 9.0;
ptr = ptr - 3;
*ptr = 6.0;
ptr += 2;
*ptr = 7.0;
Data Table
Name Type Description Value
a[0] float float array element (variable) ?
a[1] float float array element (variable) ?
a[2] float float array element (variable) 3.14
a[3] float float array element (variable) ?
ptr float * float pointer variable address of a[3]
*ptr float de-reference of float pointer
variable
?

42. 42
Pointer Arithmetic and Array
float a[4];
float *ptr;
ptr = &(a[2]);
*ptr = 3.14;
ptr++;
*ptr = 9.0;
ptr = ptr - 3;
*ptr = 6.0;
ptr += 2;
*ptr = 7.0;
Data Table
Name Type Description Value
a[0] float float array element (variable) ?
a[1] float float array element (variable) ?
a[2] float float array element (variable) 3.14
a[3] float float array element (variable) 9.0
ptr float * float pointer variable address of a[3]
*ptr float de-reference of float pointer
variable
9.0

43. 43
Pointer Arithmetic and Array
float a[4];
float *ptr;
ptr = &(a[2]);
*ptr = 3.14;
ptr++;
*ptr = 9.0;
ptr = ptr - 3;
*ptr = 6.0;
ptr += 2;
*ptr = 7.0;
Data Table
Name Type Description Value
a[0] float float array element (variable) ?
a[1] float float array element (variable) ?
a[2] float float array element (variable) 3.14
a[3] float float array element (variable) 9.0
ptr float * float pointer variable address of a[0]
*ptr float de-reference of float pointer
variable
?

44. 44
Pointer Arithmetic and Array
float a[4];
float *ptr;
ptr = &(a[2]);
*ptr = 3.14;
ptr++;
*ptr = 9.0;
ptr = ptr - 3;
*ptr = 6.0;
ptr += 2;
*ptr = 7.0;
Data Table
Name Type Description Value
a[0] float float array element (variable) 6.0
a[1] float float array element (variable) ?
a[2] float float array element (variable) 3.14
a[3] float float array element (variable) 9.0
ptr float * float pointer variable address of a[0]
*ptr float de-reference of float pointer
variable
6.0

45. 45
Pointer Arithmetic and Array
float a[4];
float *ptr;
ptr = &(a[2]);
*ptr = 3.14;
ptr++;
*ptr = 9.0;
ptr = ptr - 3;
*ptr = 6.0;
ptr += 2;
*ptr = 7.0;
Data Table
Name Type Description Value
a[0] float float array element (variable) 6.0
a[1] float float array element (variable) ?
a[2] float float array element (variable) 3.14
a[3] float float array element (variable) 9.0
ptr float * float pointer variable address of a[2]
*ptr float de-reference of float pointer
variable
3.14

46. 46
Pointer Arithmetic and Array
float a[4];
float *ptr;
ptr = &(a[2]);
*ptr = 3.14;
ptr++;
*ptr = 9.0;
ptr = ptr - 3;
*ptr = 6.0;
ptr += 2;
*ptr = 7.0;
Data Table
Name Type Description Value
a[0] float float array element (variable) 6.0
a[1] float float array element (variable) ?
a[2] float float array element (variable) 7.0
a[3] float float array element (variable) 9.0
ptr float * float pointer variable address of a[2]
*ptr float de-reference of float pointer
variable
7.0

47. 47
Pointer Arithmetic and Array
 Type of a is float *
 a[2]  *(a + 2)
ptr = &(a[2])
 ptr = &(*(a + 2))
 ptr = a + 2
 a is a memory address
constant
 ptr is a pointer variable
float a[4];
float *ptr;
ptr = &(a[2]);
*ptr = 3.14;
ptr++;
*ptr = 9.0;
ptr = ptr - 3;
*ptr = 6.0;
ptr += 2;
*ptr = 7.0;

48. Pointers and arrays
 Example
 Pointers and character strings
 example
48

49. 49
More Pointer Arithmetic
 What if a is a double array?
 A double may occupy more memory slots!
 Given double *ptr = a;
 What’s ptr + 1 then?
Addr Content Addr Content Addr Content Addr Content
1000 a[0]: 37.9 1001 … 1002 … 1003 …
1004 a[1]: 1.23 1005 … 1006 … 1007 …
1008 a[2]: 3.14 1009 … 1010 … 1011 …

50. 50
More Pointer Arithmetic
 Arithmetic operators + and – auto-adjust
the address offset
 According to the type of the pointer:
 1000 + sizeof(double) = 1000 + 4 = 1004
Addr Content Addr Content Addr Content Addr Content
1000 a[0]: 37.9 1001 … 1002 … 1003 …
1004 a[1]: 1.23 1005 … 1006 … 1007 …
1008 a[2]: 3.14 1009 … 1010 … 1011 …

51. Array of string
 Pointer to array of string: A pointer which pointing to an
array which content is string, is known as pointer to array of
strings.
#include<stdio.h>
int main()
{
char *array[4]={"c","c++","java","sql"};
char *(*ptr)[4]=&array;
printf("%s ",++(*ptr)[2]);
return 0;
}
51

52. Array of string
 Pointer to array of string: A pointer which pointing to an
array which content is string, is known as pointer to array of
strings.
#include<stdio.h>
int main()
{
char *array[4]={"c","c++","java","sql"};
char *(*ptr)[4]=&array;
printf("%s ",++(*ptr)[2]);
return 0;
}
52
Output: ava

53. 53

54. example
#include<stdio.h>
int main(){
static char *s[3]={"math","phy","che"};
typedef char *( *ppp)[3];
static ppp p1=&s,p2=&s,p3=&s;
char * (*(*array[3]))[3]={&p1,&p2,&p3};
char * (*(*(*ptr)[3]))[3]=&array;
p2+=1;
p3+=2;
printf("%s",(***ptr[0])[2]);
return 0;
} 54

55. example
#include<stdio.h>
int main(){
static char *s[3]={"math","phy","che"};
typedef char *( *ppp)[3];
static ppp p1=&s,p2=&s,p3=&s;
char * (*(*array[3]))[3]={&p1,&p2,&p3};
char * (*(*(*ptr)[3]))[3]=&array;
p2+=1;
p3+=2;
printf("%s",(***ptr[0])[2]);
return 0;
} 55
Output: che

56. As we know p[i]=*(p+i)
(***ptr[0])[2]=(*(***ptr+0))[2]=(***ptr)[2]
=(***(&array))[2] //ptr=&array
=(**array)[2] //From rule *&p=p
=(**(&p1))[2] //array=&p1
=(*p1)[2]
=(*&s)[2] //p1=&s
=s[2]=”che” 56

57. Example
int main()
{ int i,j,temp1,temp2;
int arr[8]={5,3,0,2,12,1,33,2};
int *ptr;
for(i=0;i<7;i++){
for(j=0;j<7-i;j++){
if(*(arr+j)>*(arr+j+1)){
ptr=arr+j;
temp1=*ptr++;
temp2=*ptr;
*ptr--=temp1;
*ptr=temp2;
} } } 57

58. example
int main()
{
static float farray[]
[3]={0.0f,1.0f,2.0f,3.0f,4.0f,5.0f,6.0f,7.0f,8.0f};
float (*array[3])[3]={&farray[0],&farray[1],&farray[2]};
float (*(*ptr)[])[3]=&array;
printf("%f ",2[(*(**ptr+1))]);
return 0;
}
58

59. example
int main()
{
static float farray[]
[3]={0.0f,1.0f,2.0f,3.0f,4.0f,5.0f,6.0f,7.0f,8.0f};
float (*array[3])[3]={&farray[0],&farray[1],&farray[2]};
float (*(*ptr)[])[3]=&array;
printf("%f ",2[(*(**ptr+1))]);
return 0;
}
59
Output: 5.000000

60. Dynamic memory Allocation
 Malloc –
Use - The C library function void *malloc(size_t
size) allocates the requested memory and returns a
pointer to it
Syntax - void *malloc(size_t size)
Where size -- This is the size of the memory block, in
bytes.
Return Value - This function returns a pointer to the
allocated memory, or NULL if the request fails.
60

61. example
int main()
{ char *str; /* Initial memory allocation */
str = (char *) malloc(15);
strcpy(str, "tutorialspoint");
printf("String = %s, Address = %un", str, str);
return(0);
}
61

62. example
int main()
{ char *str; /* Initial memory allocation */
str = (char *) malloc(15);
strcpy(str, "tutorialspoint");
printf("String = %s, Address = %un", str, str);
return(0);
}
62
Output -
String = tutorialspoint, Address = 355090448 String =
tutorialspoint.com, Address = 355090448

63. Dynamic Memory Allocation
 Calloc () –
The C library function void *calloc(size_t nitems, size_t
size) allocates the requested memory and returns a pointer to
it. The difference in malloc and calloc is that malloc does not
set the memory to zero where as calloc sets allocated memory
to zero.
Syntax - void *calloc(size_t nitems, size_t size)
 Parameters
nitems -- This is the number of elements to be allocated.
size -- This is the size of elements.
 Return Value
This function returns a pointer to the allocated memory, or NULL if
the request fails.
63

64. example
int main()
{ int i, n; int *a;
printf("Number of elements to be entered:");
scanf("%d",&n);
a = (int*)calloc(n, sizeof(int)); printf("Enter %d
numbers:n",n);
for( i=0 ; i < n ; i++ )
{ scanf("%d",&a[i]); }
printf("The numbers entered are: ");
for( i=0 ; i < n ; i++ )
{ printf("%d ",a[i]);
}
return(0); } 64

65.  Number of elements to be entered:3
Enter 3 numbers: 22 55 14 The
numbers entered are: 22 55 14
65

66. Difference
66

67.  Free()
The C library function void free(void
*ptr) deallocates the memory
previously allocated by a call to calloc,
malloc, or realloc.
67

68. DMA functions
 realloc()
Use- can reduce or maximize previously allocated
memory
Syntax – ptr = realloc(ptr,newsize);
68

69. Generic pointer
void pointer in c is known as generic pointer. Literal
meaning of generic pointer is a pointer which can
point type of data.
Example:
void *ptr;
Here ptr is generic pointer.
69

70. Generic pointer
int main()
{void *ptr;
printf("%d",*ptr);
return 0;
}
70

71. Generic pointer
int main()
{
void *ptr;
printf("%d",*ptr);
return 0;
}
71
Output: Compiler error
1. We cannot dereference generic pointer.

72. Generic pointer
int main()
{
void *ptr;
printf("%d",sizeof(ptr));
return 0;
}
72
Output: 2
Explanation: Size of any
type of near pointer in c is
two byte.
We can find the size of generic pointer using
sizeof operator.

73. Generic Pointer
int main(){
char c='A';
int i=4;
void *p;
char *q=&c;
int *r=&i;
p=q;
printf("%c",*(char *)p);
p=r;
printf("%d",*(int *)p);
return 0;
}
73
Output: A4
Generic pointer can hold
any type of pointers like
char pointer, struct pointer,
array of pointer etc without
any typecasting.

74. Generic Pointer
4. Any type of pointer can hold generic pointer without any
typecasting.
5. Generic pointers are used when we want to return such pointer
which is applicable to all types of pointers. For example return
type of malloc function is generic pointer because it can
dynamically allocate the memory space to stores integer, float,
structure etc. hence we type cast its return type to appropriate
pointer type
74

75. Null pointer
Literal meaning of NULL pointer is a pointer which is pointing to
nothing. NULL pointer points the base address of segment.
Examples of NULL pointer:
1. int *ptr=(char *)0;
2. float *ptr=(float *)0;
3. char *ptr=(char *)0;
4. double *ptr=(double *)0;
5. char *ptr=’0’;
6. int *ptr=NULL;
75

76. Null Pointer
What is meaning of NULL?
 NULL is macro constant which has been defined in
the heard file stdio.h, alloc.h, mem.h, stddef.h and
stdlib.h as
76

77. int main()
{
if(!NULL)
printf("I know preprocessor");
else
printf("I don't know preprocessor");
return 0;
}
Output: I know preprocessor
Explanation:
!NULL = !0 = 1
77

78. int main(){
int i;
static int count;
for(i=NULL;i<=5;){
count++;
i+=2;
}
printf("%d",count);
return 0;
 }
78
Output: 3

79. Example – Null pointer
int main()
{#ifndef NULL
#define NULL 5
#endif
printf("%d",NULL+sizeof(NULL));
return 0;
}
79
Output: 2
Explanation:
NULL+sizeof(NULL)
=0+sizeoof(0)
=0+2 //size of int data
type is two byte.

80. int main()
{
char *str=NULL;
strcpy(str,"c-pointer.blogspot.com");
printf("%s",str);
return 0;
}
80
Output: (null)
We cannot copy
any thing in the
NULL pointer.

81. Wild pointer
Wild pointer:
A pointer in c which has not been initialized is known as wild pointer.
81
Output: Any address
Garbage value#include<stdio.h>
int main()
{
int *ptr;
printf("%un",ptr);
printf("%d",*ptr);
return 0;
}

82. Wild Vs Null
82
 There is difference between the NULL
pointer and wild pointer. Null pointer
points the base address of
segment while wild pointer doesn’t point
any specific memory location.

83. Dangling pointer:
If any pointer is pointing the memory
address of any variable but after some
variable has deleted from that memory
location whilepointer is still pointing
such memory location. Such pointer is
known as dangling pointer and this
problem is known as dangling pointer
problem.
83

84.  Initial
 Later :
84

85. Near pointer:
 The pointer which can points only 64KB
data segment or segment number 8 is
known as near pointer.
85

86. Near Pointer
86
•Near pointer cannot
access beyond the
data segment like
graphics video
memory, text video
memory etc.
•Size of near pointer
is two byte.
•With help keyword
near, we can make
any pointer as near
pointer.

87. Near pointer
int main()
{
int x=25;
int near* ptr;
ptr=&x;
printf(“%d”,sizeof ptr);
return 0;
}
87
Output: 2

88. Far pointer
 The pointer which can point or access
whole the residence memory of RAM
i.e. which can access all 16 segments is
known as far pointer
88

89. 89
Size of far pointer is 4
byte or 32 bit

90. Far pointer
int main()
{
int x=10;
int far *ptr;
ptr=&x;
printf("%d",sizeof ptr);
return 0;
}
90
Output: 4
Limitation of far pointer:
We cannot change or modify the
segment address of given far
address by applying any
arithmetic operation on it. That is
by using arithmetic operator we
cannot jump from one segment to
other segment. If you will
increment the far address beyond
the maximum value of its offset
address instead of incrementing
segment address it will repeat its
offset address in cyclic order.

91. Huge Pointer
 The pointer which can point or access
whole the residence memory of RAM
i.e. which can access all the 16
segments is known as huge pointer.
91

92. 92
Size of huge
pointer is 4 byte
or 32 bit.

93. 93
Summary
 A pointer stores the address (memory
location) of another entity
 Address-of operator (&) gets the
address of an entity
 De-reference operator (*) makes a
reference to the referee of a pointer
 Pointer and array
 Pointer arithmetic