Pointers in C++ ( CBSE-XII)
Introduction to Pointer, Declaration and Initialization of Pointer;
Dynamic memory allocation/deallocation
operators: new, delete; Pointers and Arrays: Array of Pointers, Pointer
to an array (1 dimensional
array), Function returning a pointer, Reference variables and use of alias;
Function call by reference. Pointer
to structure: De-reference/Deference operator: *, ->; self referencial
structure;
6.1 Introduction
The C and the C++ languages are still
existing popular programming languages in the computer world. The major reason
behind this is pointers. Pointers help
to refer the memory locations to store and access the data into computer
memory. Pointers are also used to access the more than one memory locations sequentially.
Pointers also help to allocate memory locations dynamically.
Pointer is a special type variable,
which does not store the values, rather it store the address of another
variable. This concept
might sound the unnecessarily complicated, but it implies a number of
advantages like for instance more efficient programming code, faster execution
of program and saving of memory. Object oriented programming such as C++ always
gets these advantages when copying objects or sending objects to functions.
The concept of pointer is the unique
concept in the C++ programming language, which is not available in the latest
languages Java and Visual Basic. Therefore, C++ is still growing the in the
computer era since 1980.
This chapter will explain the basic
concepts of pointers and their use. You will learn use of pointers with
different data types. The method of declaring and assigning the values to the
pointer are elaborated in the student’s point of view. This chapter also
examine the analogy between pointers and arrays and how to use pointers as
parameters for the functions.
Additionally, this chapter will explain
the concept of dynamic memory allocation, which actually does not closely
relate to pointers, but still often is used in connection with pointers.
6.2 Definition
A pointer is a variable to store the
address of another variable. This address is also refer as a memory location of
the variable, which is the address of primary memory.
In other words, a variable which is
already declared in the memory may or may not contain the value, the pointer
variable can store the address of this variable. This variable may be of any
data type can have pointer variable to store their addresses. Let’s see an
example in the figure:
int
number = 10;
The above statement shows the number is an integer
variable has the value 10. The primary memory will allocate the memory for this
variable like that:
|
10
|
The description
of above variable is:
Name of variable : number
Address of
variable in primary memory : 10011
Value of the
variable is : 10
For above variable if we defined a
pointer variable it will looks like in the memory like as given in the figure:
|
10011
|
The description of above pointer
variable is:
Name of pointer variable : Pnumber
Address of pointer
variable in primary memory : 10013
Value of the pointer
variable is : 10011
Using this concept we may access the
value of number variable using
pointer variable Pnumber, which is
described in later section of this chapter.
6.3 Declaration and
Initialization of Pointer
To declare the
pointer variable that can point to an integer value, you can use the following
syntax:
int* Pnumber;
The asterisk (*)
symbol as postfix on the type says that the variable being defined is a pointer
to an object of that type: Pnumber can point to a
place in memory that can contain a value of type int.
You must always
specify the data type pointed to by the pointer variable. Below we declare to a
double value:
double* pSize;
Below is the example
of declaring a pointer to a char value:
char* pChr;
You can as well
place the space in front of the asterisks. The declarations above could be
written:
int
*Pnumber;
double *pSize;
char *pChr;
Both variants of
pointer declarations are allowed in C++.
To assign the
address of any variable into the pointer variable we need to use the &
operator. Let see given example:
int number = 34;
int *pNumber = &number;
Here a pointer
variable pNumber is created and assigned the
address of variable number. The variable number and the pointer variable pNumber now points to the
same memory location, which means value 23.
You can’t directly
assign a fixed value to the pointer in the declaration:
int *pNumber = 34; //wrong
assignment
since currently there is no specific
memory locational pointed to by pNumber. However, when pNumber has got its
memory address, we can change the value in the location indicated by pNumber:
*pNumber = 25;
Here we must remember to use asterisk
together with the name of the pointer variable. The program then understand that
it is the value that is to be changed.
Compare this to this erroneous
statement:
pNumber = 25; //wrong
statement
This would mean that we updated the
address pointed to by pNumber. The address 25
would be pointed to, which of course is erroneous.
In the concept of pointers two operators
are generally used :
|
Operator
|
Meaning
|
|
*
|
the
content of
|
|
&
|
the
address to
|
To
understand the use these operators, let see an example:
Example
6.1: Program to show the use of * and & operators.
# include <
iostream.h >
void main()
{
int
num = 10;
int *p = #
cout << “\n num :” << num
<< endl;
cout << “\n &num :” << &num
<< endl;
cout << “\n *(&num) :” << *(&num)
<< endl;
cout << “\n p :” << p <<
endl;
cout << “\n &p :” << &p
<< endl;
cout
<< “\n *(&p) :” << *(&p) << endl;
cout
<< “\n *p :” << *p << endl;
}
OUTPUT
num : 10 // content of num
&num : <address of num> // address of num
*(&num) : 10 // content of address of num
p : <address of num> // content of p
&p : <address of p> // address of p
*(&p) :
<address of num> // content
of address of p
*p : 10 //
content of address stored at p means content of num
Now have a look at how pointers work in
connection with string variables, i.e. arrays of char type.
Example
6.2: Program to use the pointers with string.
#include <
iostream.h >
void main()
{
char
name[] = ”Raj Kumar”;
char*
pname = name;
cout << name << endl;
cout
<< *pname << endl;
cout << pname << endl;
pname++;
cout << pname << endl;
pname+=5;
cout << pname << endl;
}
OUTPUT
Raj Kumar
R
Raj Kumar
aj Kumar
mar
In
the above example, output is explained below statement by statement:
cout << name <<
endl;
:Statement prints the content of variable name,
cout
<< *pname << endl; :Statement prints the content of first
element of array,
cout
<< pname << endl; :
which should actually print the address stored in pname, but cout
performs a reinterpretation . it takes the content in the memory locations
pointed to by pname, i.e. the character ‘R’, and prints character by character
until the null character is found. This means, it printed ‘Raj Kumar’ which is
entire string.
pname++; : This statement
increase the pointing location of pointer variable pname, now it is
pointing at the second element of array, i.e. the character ‘a’.
cout << pname << endl; : after increasing the
location of pointer, it printed ‘aj Kumar’ which is entire string from second
location.
pname+=5; :
This statement will increase the 5 more pointing location of pointer variable
from current location. Therefore, it printed ‘mar’ which is entire string from second
location.
Using
pointer the value of ordinary variable may be updated directly. Let see another
example, where the ordinary variables are updated using pointers automatically.
Example
6.3 : Program to update the variables using pointers.
#include <
iostream.h >
void main()
{
int
a = 10;
int*
ptr = &a;
cout << “\n Value of a = ” << a;
*ptr = *ptr + 10;
cout << “\n Value of a = ” <<
a;
*ptr = 300;
cout << “\n Value of a = ” <<
a;
*ptr = a / 2;
cout << “\n Value of a = ” <<
a;
}
OUTPUT
Value of a =
10
Value of a =
20
Value of a =
300
Value of a =
150
Using
pointer the values of more than ordinary variables may be stored separately.
Let see another example, where the ordinary variables are stored using pointers
and displayed accordingly.
|
ptr
|
|
a
|
|
b
|
|
c
|
Example
6.4 : Program to store address of many variables using pointers.
#include <
iostream.h >
void main()
{
int
a = 10, b = 20, c = 30;
int*
ptr;
ptr
= &a;
cout << “\n Value of a = ” << *ptr;
ptr
= &b;
cout << “\n Value of b = ” <<
*ptr;
ptr
= &c;
cout << “\n Value of c = ” <<
*ptr;
}
OUTPUT
Value of a =
10
Value of b =
20
Value of c =
30
Using
multiple pointers the address of any single ordinary variable may be stored.
Let see another example, where the only one ordinary variable is stored in
multiple pointers and displayed accordingly.
|
a
|
|
P11
|
|
P2
|
|
P3
|
Example
6.4 : Program to store address of one variable into multiple pointers.
#include <
iostream.h >
void main()
{
int
a = 10;
int
*p1, *p2, *p3;
p1
= &a;
p2
= &a;
p3
= &a;
cout
<< “\n p1, p2 and p3 pointing on same address:” << &a;
cout
<< “\n Value of a using pointer p1 = ” << *p1;
cout
<< “\n Value of a using pointer p2 = ” << *p2;
cout
<< “\n Value of a using pointer p3 = ” << *p3;
a
= 20;
cout
<< “\n Value of a after change :” << a;
cout
<< “\n Value of a using pointer p1 = ” << *p1;
cout
<< “\n Value of a using pointer p2 = ” << *p2;
cout
<< “\n Value of a using pointer p3 = ” << *p3;
*p1
= *p1+10;
cout
<< “\n Value of a after change :” << a;
cout
<< “\n Value of a using pointer p1 = ” << *p1;
cout
<< “\n Value of a using pointer p2 = ” << *p2;
cout
<< “\n Value of a using pointer p3 = ” << *p3;
}
OUTPUT
p1, p2 and p3
pointing on same address: 1104
Value of a using
pointer p1 = 10
Value of a
using pointer p2 = 10
Value of a
using pointer p3 = 10
Value of a
after change = 20
Value of a
using pointer p1 = 20
Value of a
using pointer p2 = 20
Value of a
using pointer p3 = 20
Value of a
after change = 30
Value of a
using pointer p1 = 30
Value of a
using pointer p2 = 30
Value of a
using pointer p3 = 30
6.5 Dynamic memory allocation/de-allocation
In
the C++ programming language, there are two ways that memory gets allocated for
data storage:
1.
Static Memory Allocation
The memory for defined variables is
allocated by the compiler itself. The exact size and data type of variable to store
must be known at the time of compilation. Therefore, standard array
declarations need the constant size.
2.
Dynamic Memory Allocation
The memory allocated for the variables
during the run time. The dynamically allocated space usually placed in a
program segment known as the heap or the free store. In this allocation exact
amount of space or number of items does not have to be known by the compiler in
advance. Therefore, for dynamic memory allocation, pointers are crucial.
We
can dynamically allocate storage space while the program is running, but we
cannot create new variable names during the execution.
Therefore
to implement the concept of dynamic allocation, it requires two steps:
1.
Creating
the dynamic space.
2.
Storing
its address in a pointer (so that the space can be accessed)
In
the C++, new operator is
used to create the dynamic memory space.
De-allocation is the process
to clean-up the space being used for variables or other data storage. The compile
time variables are automatically de-allocated based on their known extent (this
is the same as scope for "automatic" variables). It is the
programmer's job to de-allocate dynamically created space, to de-allocate
dynamic memory space the delete operator is
available in C++ programming language.
6.5.1
new and delete operators
In
the C++, for allocation and de-allocation of memory dynamically, new and delete operators are used.
To
allocate space dynamically, use the unary operator new, followed by the type
being allocated.
new int;
// dynamically allocates an int
new double;
// dynamically allocates a double
These
above statements are not very useful by themselves, because the allocated
spaces have no names, and the new
operator returns the starting address of the allocated space, and this address
can be stored in a pointer:
int * p;
// declare a pointer p
p = new int;
// dynamically allocate an int and load address into p
double * d;
// declare a pointer d
d = new double; // dynamically allocate a
double and load address into d
Consider
the following example for dynamically allocation and de-allocation of the
variables.
Example
6.4 : Program to allocate and de-allocate the dynamic space using pointers.
#include <
iostream.h >
void main()
{
int
*p1;
p1
= new int; // dynamic memory
allocation
*p1
= 300;
cout
<< “\n Value inside the p1 = ” << *p1;
delete p1; //free the dynamically allocated memorys
}
OUTPUT
Value inside
the p1 = 300
Using
the new and delete operators, we can create arrays at runtime by dynamic memory
allocation and de-allocation. The general form for doing this is:
p_var
= new array_type[size];
size
specifies the number of elements in the array.
To
free the memory of an array we use:
delete[]
p_var;
Let
see the given example for the above explanation.
Example
6.5 : Program to create dynamic array using pointers.
#include <
iostream.h >
void main()
{
int
*p;
p
= new int[10]; // dynamic
allocation for array of 10 elements
for(int
i = 0; i < 10; i++)
p[i]
= i;
cout
<< “\n content of array are : ” << endl;
for(i
= 0; i < 10; i++)
cout
<< p[i] << endl;
delete[] p; //free the array memories
}
OUTPUT
content of
array are :
0
1
2
3
4
5
6
7
8
9
6.6 Pointers and Arrays
As
we know that for an array, compiler declares the memory in contiguous memory
locations. The base address of array points on the first element of the array.
The array always has a constant name for accessing the elements. The pointer
helps to arrays with following features and advantages:
Advantages
of pointers over arrays:
-
Using
pointers we can save the memory which are unused by the declaring of arrays.
-
Using
pointers we can access the memory locations of arrays easily.
-
Using
pointers we can execute the program fast.
6.7
Pointers to an Array
Suppose
an array is declared like that:
int
arr[5] = {1, 2, 3, 4, 5};
Suppose
the base address of arr is 1000 and
assuming that each integer requires two bytes, the five elements will be stored
as following format:
|
Index →
|
arr[0]
|
arr[1]
|
arr[2]
|
arr[3]
|
arr[4]
|
|
Values →
|
1
|
2
|
3
|
4
|
5
|
|
Address →
|
1000
|
1002
|
1004
|
1006
|
1008
|
The
name arr is defined as a
constant pointer pointing to the first element, arr[0] and therefore the value of arr is 1000, the
location where arr[0]
is
stored. That is:
arr =
&arr[0] = 1000
If
we declare p as an integer
pointer, then we can make the pointer p to point to the array arr by the
following assignment:
p = arr;
This is also equivalent to
p = &arr[0];
Now,
we can access every value of arr
using p++ to move from
one element to next element. The relationship between pointer variable p and array arr is shown as:
p = &arr[0]; // means base address 1000
p+1 = &arr[1]; // means address 1002
p+2 = &arr[2]; // means address 1004
p+3 = &arr[3]; // means address 1006
p+4 = &arr[4]; // means address 1008
You
may notice that the address of an element is calculated using its index and the
scale factor of the data type. For instance:
Address of arr[3] = base address + ( 3 × scale factor of int)
= 1000 + (3 × 2)
= 1006
When
handling arrays, instead of using array indexing, we can use pointers to access
array elements. Note that *(p+3)
gives the value of arr[3]. The pointer
accessing method is much faster than array indexing.
Let
see an example that illustrate the use of pointer accessing method.
Example
6.6 : Program to access the array elements using pointers.
#include <
iostream.h >
void main()
{
int
*p, i = 0;
int
arr[5] = {1, 2, 3, 4, 5};
p
= arr;
cout
<< “\n content of array are : ” << endl;
while(i
< 5)
{
cout << “\n arr[”
<< i++ << ”] = ” << *p;
p++;
}
}
OUTPUT
content of
array are :
arr[0] = 1
arr[1] = 2
arr[2] = 3
arr[3] = 4
arr[4] = 5
Let
review another example that also produce same output.
Example
6.7 : Program to access the array elements using pointers.
#include <
iostream.h >
void main()
{
int
*p, i = 0;
int
arr[5] = {1, 2, 3, 4, 5};
p
= arr;
cout
<< “\n content of array are : ” << endl;
while(i
< 5)
{
cout
<< “\n arr[” << i << ”] = ” << *(p + i);
i++;
}
}
OUTPUT
content of
array are :
arr[0] = 1
arr[1] = 2
arr[2] = 3
arr[3] = 4
arr[4] = 5
As
you saw in the example 6.2 about the string with pointers, actually strings are
treated like character arrays and therefore they are declared and initialized
as follows:
char st[7] = “Welcome” ;
in
above statement compiler automatically adds the null character ‘\0’ at the end
of the string. Pointers provides an
alternate method to create the string.
char *st = “Welcome”;
This
create a string for the literal and then stores its address in the variable.
The pointer variable now points to the first character of the string “Welcome”
as:
|
|
e
|
l
|
c
|
o
|
m
|
e
|
\0
|
st
We
can also use the run-time assignement for giving values to a string pointer.
Example
char *st;
st = “Welcome”;
Note
that the assignment
st = “Welcome”;
is
not a string copy, because the variable st is pointer, not a string. we can print the content of string st using cout as follows:
cout << st;
using
pointer we can find out the length of string using the pointer and their
address concept. Let see the example given below:
Example
6.7 : Program to find out the length of string using pointers.
#include <
iostream.h >
void main()
{
int
len = 0;
int
*ch, *str;
str
= ”INDIA”;
ch
= str;
while(*ch
!= ‘\0’)
{
cout << *ch << endl;
ch++;
}
len
= ch – str;
cout
<< “\n Length of the string is = ” << len;
}
OUTPUT
I
N
D
I
A
Length of the
string is = 5
6.8
Array of pointers
Like
a simple array, pointers may be defined in the form of arrays. consider the
following array of strings:
char name[4][20];
This
declaration says that the name
is a double dimensional array, may contain 4 strings with maximum length of 20
characters (including null character). The total storage requirements for the name array are 80
bytes. But we know that rarely all strings will be equal length. Therefore, we
may use the pointers instead of making fixed size for each string. For example,
we may declare array of pointers:
char
*name[4] = {
“Raj Kumar”,
“Neha Rani”,
“Rakesh”,
“Sonu”
};
Above
declaration has array of pointers, where name to be an array of four pointers to characters, each
pointer pointing to a particular name as:
name[0] Ã Raj
Kumar
name[1] Ã Neha
Rani
name[2] Ã Rakesh
name[3] Ã Sonu
This
declaration allocates only 32 bytes, which is sufficient to hold all the
characters as shown below:
|
R
|
a
|
j
|
|
K
|
u
|
m
|
a
|
r
|
\0
|
|
N
|
e
|
h
|
a
|
|
R
|
a
|
n
|
i
|
\0
|
|
R
|
a
|
k
|
e
|
s
|
h
|
\0
|
|
|
|
|
S
|
o
|
n
|
u
|
\0
|
|
|
|
|
|
The
following statement would print out all the three names:
for(int i = 0; i <= 2; i++)
cout << name[i];
To
access the j-th character in the i-th name, we may write as:
*(name[i]=j)
The
character arrays with the row of varying length are called ragged array and
are better handled by pointers.
6.8
Function and Pointers
Pointers
also support to pass the arguments to functions, when we pass the addresses to
a function, the parameters receiving addresses should be pointers. The process
of calling a function using pointers to pass the addresses of variables is
known as call by reference and the process of passing the actul
value of variables is known as call by value. The function which
is called by reference can change the value of the variable used in the
call. Let see an example of ‘call by value’ and ‘call by reference’:
Example
6.8 : Program to show the call by value and call by reference.
#include <
iostream.h >
void change(
int x );
void p_change(
int *y);
void main()
{
int
A = 10;
cout
<< “\n value of A : ” << A;
change(A);
cout
<< “\n value of A after calling function change : ” << A;
p_change(&A);
cout
<< “\n value of A after calling function p_change : ” << A;
}
void change (
int x ) // function call by value
{
x = x + 10;
}
void p_change
( int *y ) // function call by
reference
{
*y = *y + 20;
}
OUTPUT
value of A : 10
value of A
after calling function change : 10
value of A
after calling function p_change : 30
Above
example clearly shows the difference between call by value and call
by reference. The function change(int x) shows the use of call by
value and p_change(int *y) shows the use of call by reference.
When
function change() is called it
passes the value of variable A,
which copied to the function parameter x and inside the function value has been updated,
which is not effect on the actual argument A in the main. On the other hand when function p_chage() is called it
passes the address of
A
instead of value, which copied to the pointer variable y, and inside the
function content of pointer variable has been updated, which directly updated
the actual argument A in the
main.
Using
this concept we can swap the values of two variables, which also not possible
in call by value. Let see another example:
Example
6.8 : Program to swap the values of two variables using pointers.
#include <
iostream.h >
void
interchange( int x, int y );
void swap( int
*x, int *y);
void main()
{
int
A = 10, B = 15;
cout
<< “\n value of A : ” << A;
cout
<< “\n value of B : ” << B;
interchange(A,B);
cout
<< “\n After calling interchange function ”;
cout
<< “\n value of A : ” << A;
cout
<< “\n value of B : ” << B;
swap(&A,&B);
cout
<< “\n After calling swap function ”;
cout
<< “\n value of A : ” << A;
cout
<< “\n value of B : ” << B;
}
void
interchange ( int x, int y ) //
function call by value
{
int temp;
temp
= x;
x
= y;
x
= temp;
}
void swap (
int *x, int *y ) // function call by
reference
{
int
temp;
temp
= *x;
*x
= *y;
*x
= temp;
}
OUTPUT
value of A : 10
value of B : 15
After calling
interchange function
value of A : 10
value of B : 15
After calling
swap function
value of A : 15
value of B : 10
6.9
Function returning Pointers
We
have seen in earlier examples that a function can return a single value by its
name or return multiple values through pointer parameters. Since pointers are a
data type in C++, we can also force a function to return a pointer to the
calling function. Let see an example for the same.
Example
6.9 : Program to return pointers by functions.
#include <
iostream.h >
int *max( int *x,
int *y );
int *min( int
*x, int *y);
void main()
{
int
A = 10, B = 15;
int
*p;
p
= max(&A, &B);
cout
<< “\n Big value is : ” << *p;
p
= min(&A, &B);
cout
<< “\n Small value is : ” << *p;
}
int *max ( int
*x, int *y ) // function call by
reference
{
if( *x > *y )
return( x );
else
return( y );
}
int *min ( int
*x, int *y ) // function call by
reference
{
if( *x < *y )
return( x );
else
return( y );
}
OUTPUT
Big value is: 15
Small value is:
10
The function max()and min() receive the
addresses of variable A and B, decides which
one is larger and smaller using pointers x and y and then returns the address of its location
respectively. The returned address is then assigned to the pointer variable p in the calling
function.
6.10
Reference Variables and Alias
Like
a pointer variables C++ also supports reference variables which works same like
pointer variables only the little bit syntaxes are change. Let see an example
for the same.
Example
6.10 : Program to show the use of reference variables.
#include <
iostream.h >
void update(
int &x );
void main()
{
int
A = 10;
cout
<< “\n original value of A : ” << A;
update(A);
cout
<< “\n value of A after calling update function : ” << A;
int
&b=A; //declaration of
reference variable
b=1000;
cout
<< "\n value of A after updating reference variable : "
<< A;
}
void update (
int &x) //function with reference
variable
{
x = 100;
}
OUTPUT
original value
of a : 10
value of a
after calling update function : 100
value of A
after updating reference variable : 1000
The
function update()receive the value
of variable A into the
reference variable x, and updated
the value of x which directly
effects on the original value of variable A. In the second case an integer reference variable &b is created and
updated which also effects on the original value of A.
Reference
variable as an Alias
A
reference variable is also used as an alias, that is, another name for
an already existing variable. Once a reference is initialized with a variable,
either the variable name or the reference name may be used to refer to the
variable.
Reference
variables are often confused with pointers but there are major differences
between reference variables and pointer variables are:
|
Reference variable
|
Pointer variable
|
|
·
Reference variable don’t have NULL value.
|
·
Pointer variable may has the NULL value.
|
|
·
Once a reference variable is initialized to an
object, it cannot be changed to refer to another object.
|
·
Pointers variable can be pointed to another object
at any time.
|
|
·
A reference variable must be initialized when it
is created.
|
·
Pointer variable can be initialized at any time.
|
Let
see another example for the use as alias.
Example
6.10 : Program to show the use of reference variables as alias.
#include <
iostream.h >
void main()
{
int
A ;
float
B;
//declaration
of reference variables for A and B
int
&X = A;
float
&Y = B;
A
= 10;
cout
<< “\n value of A : ” << A;
cout
<< “\n value of reference A : ” << X;
B
= 11.37;
cout
<< “\n value of B : ” << B;
cout
<< “\n value of reference B : ” << Y;
//Updating
the reference variables
X
= X + 1;
Y
= Y + 1.0;
cout
<< “\n Reference variables are updated.”;
cout
<< “\n value of A : ” << A;
cout
<< “\n value of B : ” << B;
}
OUTPUT
value of A : 10
value of
reference A : 10
value of B : 11.37
value of
reference B : 11.37
Reference
variables are updated.
value of A : 11
value of B : 12.37
6.10
Structure and Pointers
You
can declare pointers to structures in the same way as declaring pointers to
other data types. Let see an example:
struct student
{
char
name[20];
int clas;
float marks;
};
student stud;
student *st;
The
address of structure variable can be initialized similar to the normal way:
st =
&stud;
The
advantage is to be able to use pointer arithmetic to step through the different
structure variables:
st++;
This
statement moves to the next structure variable.
With
a pointer to a structure you are not allowed to use the dot (.)operator as
delimiter between the variable and member. You must use the (->) characters. The
symbol -> is called the arrow
operator ( also known as dereference operator) and is made up of
minus sign and a greater than sign. Let
see a program example for the use of structure to pointer:
Example
6.10 : Program to show the use of structure and pointers.
#include <
iostream.h >
struct student
{
char
name[20];
int clas;
float marks;
};
void main()
{
student stud[3];
student *st;
for( st = stud; st < stud + 3; st++)
{
cout << “\n enter name of
student :”;
cin >> st -> name;
cout << “\n enter class of
student :”;
cin >> st -> clas;
cout << “\n enter total marks
of student :”;
cin >> st -> marks;
}
st = stud;
cout << “\n Students Records are:”;
while(st < stud + 3)
{
cout << “\n Name : ” <<
st->name;
cout << “\n class : ” <<
st->clas;
cout << “\n Total Marks : ”
<< st->marks;
st++;
}
}
OUTPUT
enter name of
student : Arush
enter class of
student : 2
enter total
marks of student : 450
enter name of
student : Dev
enter class of
student : 3
enter total
marks of student : 355
Students
Records are:
Name : Arush
class : 2
Total Marks : 450
Name : Dev
class : 3
Total Marks : 355
In
the above example, when the pointer st is incremented by one, it is made to point to the
next record. i.e. stud[1]. The statement
give below may be use alternatively:
st->name;
We
could use the notation
(*st).name;
to
access the member name. The parentheses around *st are necessary because the member
operator (.) has higher
precedence than the operator (*).
6.11
Self-referential Structure
The
structure may have another structure, which known as sub structure. But like a
recursion any structure refer itself by the use of pointers. A self-referential
structure is used to create data structures like linked lists, stacks, etc.
Following is an example of this kind of structure:
struct struct_name
{
datatype datatypename;
struct_name * pointer_name;
};
A
self-referential structure is one of the data structures which refer to the
pointer to (points) to another structure of the same type. For example, a
linked list is supposed to be a self-referential data structure. The next node
of a node is being pointed, which is of the same struct type. For example,
struct linklistnode
{
int data;
struct linklistnode *next;
};
In
the above example, the linklistnode is a
self-referential structure – because the *next is of the type struct linklistnode. The details of
linklist and stacks are define in later chapters.
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