Pointers in C Programming

POINTERS
Presented by
Er. Jasleen Kaur
Assistant Professor
Applied Science(CSE)
Chandigarh University
Gharuan (Mohali).

Pointer
• A variable that holds a memory address.
• This address is the location of another object
in the memory.
• Pointer as an address indicates where to find
an object.
Not all pointers actually contain an address
example NULL pointer.
Value of NULL pointer is 0.
10/19/2015

• Pointer can have three kinds of content in it
1) The address of an object, which can be
dereferenced.
2) A NULL pointer.
3) Invalid content, which does not point to an
object.
(If p does not hold a valid value, it can crash the
program)
• If p is a pointer to integer, then
– Int *p

It is possible in some environments to have
multiple pointer values with different
representations that point to same location in
memory.
But make sure if the memory is deleted using
delete or if original variable goes out of scope.

Declaring pointer
Data-type *name;
* is a unary operator, also called as indirection
operator.
Data-type is the type of object which the
pointer is pointing.
Any type of pointer can point to anywhere in
the memory.
* is used to declare a pointer and also to
dereference a pointer.

When you write int *,
compiler assumes that any address that it
holds points to an integer type.
 m= &count;
it means memory address of count variable is
stored into m.
& is unary operator that returns the memory
address.
i.e. & (orally called as ampersand) is returning
the address.
 so it means m receives the address of count.

Suppose, count uses memory
Address 2000 to store its value 100.
so, m=&count means m has 2000
address.
q= *m
it returns the value at address m.
value at address 2000 is 100.
so, q will return value 100.
i.e. q receives the value at address m.
count=1002000

Address-of operator(&)
• It is used to reference the memory address of
a variable.
• When we declare a variable, 3 things happen
– Computer memory is set aside for variable
– Variable name is linked to that location in memory
– Value of variable is placed into the memory that
was set aside.

Int *ptr;
declaring variable ptr which holds the value
at address of int type
 int val =1;
assigning int the literal value of 1
 ptr=&val;
dereference and get value at address stored in
ptr
int deref =*ptr
printf(“%dn”, deref);
Output will be 1

Pointer Conversions
• One type of pointer can be converted to
another type of pointer.
• int main() {
double x=100.1, y;
int *p;
p= (int *) &x; //explicit type conversion
y= *p;
}

Generic Pointer
void * pointer is called as generic pointer.
Can’t convert void *pointer to another pointer
and vice-versa.
void *pointer can be assigned to any other
type of pointer.
void * is used to specify a pointer whose base
type is unknown.
It is capable of receiving any type of pointer
argument without reporting any type of
mismatch.

Pointer Arithmetic
• There are only two arithmetic operations that
can be used on pointers
– Addition
– Subtraction
• To understand this concept, lets p1 be an
integer pointer with value 2000 address.
– int is of 2 bytes
– After expression p1++;
– P1 contains address 2002 not 2001.

• Each time p1 is incremented, it will point to
next integer.
• The same is true for decrement.
– for p1--;
– Causes value of p1 to be 1998.
• Each time a pointer is incremented, it points
to the memory location of the next element of
its base type.
• If decremented, then it points to previous
element location.
• P1=p1+12; makes p1 points to 12th element of
p1 type.

Arithmetic Rules
• You cannot multiply or divide pointers.
• You cannot add or subtract two pointers.
• You cannot apply bitwise operators to them.
• You cannot add or subtract type float or
double to or from pointers.

Pointer Comparison
• You can compare two pointers in a relational
expression, example:
if(p<q)
printf(“p points to lower memory than q n”);
• Pointer comparison are useful only when two
pointers point to a common object such as an
array.

Benefits of pointer
• Pointers are used in situations when passing actual values is
difficult or not desired.
• To return more than one value from a function.
• They increase the execution speed.
• The pointer are more efficient in handling the data types .
• Pointers reduce the length and complexity of a program.

• The use of a pointer array to character string results in
saving of data.
• To allocate memory and access it( Dynamic memory
Allocation).
• Implementing linked lists, trees graphs and many other data
structure.

How to get address of a function
/*A program to get address of a function */
#include<stdio.h>
void main()
{
void show(); /* usual way of invoking a function */
printf(“ The address of show function is=%u”, show);
}
void show()
{
printf(“ welcome to HPES!!”)
}

Uses of pointer to function
• Pointers are certainly awkward and off-putting and thus
this feature of pointer is used for invoking a function
• There are several possible uses :
(a) In writing memory resident program.
(b) In writing viruses, or vaccines to
remove the viruses.
(c) In developing COM/DCOM component
(d) In VC++ programming to connect events to
function calls.

Pointers in C Programming

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