Dynamics allocation

Constructor and Destructor

Arrays, Pointers, References, and the Dynamic Allocation
Operators
H S Rana
Center For information Technology
UPES Dehradun, India

October 3, 2012

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October 3, 2012

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Array Of Object

Example
The syntax for declaring and
using anobject array is exactly
the same as it is for any other
type of array.
class cl {
int i;
public:
void set_i(int j) { i=j; }
int get_i() { return i; }
};

H S Rana (UPES)


October 3, 2012

2 / 23


Array Of Object

Example
The syntax for declaring and
using anobject array is exactly
the same as it is for any other
type of array.
class cl {
int i;
public:
void set_i(int j) { i=j; }
};

H S Rana (UPES)

int main()
{
cl ob[3];
int i;
for(i=0; i<3; i++)
ob[i].set_i(i+1);
for(i=0; i<3; i++)
cout << ob[i].get_i()<< "n";
return 0;
}


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Array Of Object

Example
Parameterized Constructor can
be used to initialize each
object in array
class cl {
int i;
public:
cl(int j) { i=j; } // constructor
};

H S Rana (UPES)


October 3, 2012

3 / 23


Array Of Object

Example
int main()
{
cl ob[3] = {1, 2, 3}; // initializers
//Equal to cl ob[3] = { cl(1), cl(2), cl(3) };
int i;
for(i=0; i<3; i++)
cout << ob[i].get_i() << "n";
return 0;
}

H S Rana (UPES)


October 3, 2012

4 / 23


Array Of Object

Example
If an object’s constructor requires two or more arguments
class cl {
int h;
int i;
public:
cl(int j, int k) { h=j; i=k; } // constructor with 2 paramet
int get_i() {return i;}
int get_h() {return h;}
};

H S Rana (UPES)


October 3, 2012

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Array Of Object
Example
int main()
{
cl ob[3] = {
cl(1, 2), // initialize
cl(3, 4),
cl(5, 6)
};
int i;
for(i=0; i<3; i++) {
cout << ob[i].get_h();
cout << ", ";
cout << ob[i].get_i() << "n";
}
return 0;
}
H S Rana (UPES)


October 3, 2012

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Creating Initialized vs. Uninitialized Arrays
If you want to create uninitialized array
Example
class cl {
int i;
public:
cl(int j) { i=j; }
};

H S Rana (UPES)


October 3, 2012

7 / 23


Creating Initialized vs. Uninitialized Arrays
If you want to create uninitialized array
Example
class cl {
int i;
public:
cl(int j) { i=j; }
};

main function
main()
{
cl a[9]; // error,
}
H S Rana (UPES)


October 3, 2012

7 / 23


Pointer to Object
We can deﬁne pointers to objects. When accessing members of a class given a
pointer to an object, use the arrow operator instead of the dot operator.
Example
class cl {
int i;
public:
cl(int j) { i=j; }
};
int main()
{
cl ob(88), *p;
p = &ob; // get address of ob
cout << p->get_i(); // use -> to call get_i()
return 0;
}
H S Rana (UPES)


October 3, 2012

8 / 23


Pointer to Object
when a pointer is incremented, it points to the next element of its type. For
example, an integer pointer will point to the next integer.
Example
class cl {
int i;
public:
cl() { i=0; }
cl(int j) { i=j; }
int get_i() { return i;}};
int main(){
cl ob[3] = {1, 2, 3}
cl *p;
int i;
p = ob; // get start of array
for(i=0; i<3; i++) {
cout << p->get_i() << "n";
p++; // point to next object }
H S Rana (UPES) 0;}
return

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The this Pointer
When a member function is called, it is automatically passed an implicit argument
that is a pointer to the invoking object (that is, the object on which the function
is called). This pointer is called this.
Example
class pwr {
double b;
int e;
double val;
public:
pwr(double base, int exp);
double get_pwr() { return val; }
};

H S Rana (UPES)


October 3, 2012

10 / 23


The this Pointer
Example
pwr::pwr(double base, int exp)
{b = base;
e = exp;
val = 1;
if(exp==0) return;
for( ; exp>0; exp--) val = val * b;}

H S Rana (UPES)


October 3, 2012

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The this Pointer
Example
{b = base;
e = exp;
val = 1;
if(exp==0) return;
for( ; exp>0; exp--) val = val * b;}
Another Deﬁnition
{ this->b = base;
this->e = exp;
this->val = 1;
if(exp==0) return;
for( ; exp>0; exp--)
this->val = this->val * this->b;
}
H S Rana (UPES)


October 3, 2012

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The this Pointer

main function
int main()
{
pwr x(4.0, 2), y(2.5, 1), z(5.7, 0);
cout << x.get_pwr() << " ";
cout << y.get_pwr() << " ";
cout << z.get_pwr() << "n";
return 0;
}

H S Rana (UPES)


October 3, 2012

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Dynamics Allocation of Memory
Memory Allocation operators
C++ provides two dynamic allocation operators: new and delete. These
operators are used to allocate and free memory at run time.The new operator
allocates memory and returns a pointer to the start of it. The delete operator
frees memory previously allocated using new

H S Rana (UPES)


October 3, 2012

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Memory Allocation operators
C++ provides two dynamic allocation operators: new and delete. These
operators are used to allocate and free memory at run time.The new operator
allocates memory and returns a pointer to the start of it. The delete operator
frees memory previously allocated using new
General form
The general forms of new and delete are :
p_var = new type;
delete p_var;
Here, p_var is a pointer variable that receives a pointer to
memory that is large enough to hold an item of type type.
H S Rana (UPES)


October 3, 2012

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Example
#include <iostream>
#include <new>
using namespace std;
int main()
{
int *p;
try {
p = new int; // allocate space for an int
} catch (bad_alloc xa) {
cout << "Allocation Failuren";
return 1;
}
*p = 100;
cout << "At " << p << " ";
cout << "is the value " << *p << "n";
delete p;
return (UPES)
H S Rana 0;

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Initializing Allocated Memory

We can initialize allocated memory to some known value by putting an initializer
after the type name in the new statement.

H S Rana (UPES)


October 3, 2012

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We can initialize allocated memory to some known value by putting an initializer
after the type name in the new statement.
General form
p_var = new var_type (initializer);

H S Rana (UPES)


October 3, 2012

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Example
#include <iostream>
#include <new>
int main()
{
int *p;
try {
p = new int (87); // initialize to 87
return 1;
}
cout << "At " << p << " ";
cout << "is the value " << *p << "n";
delete p;
return 0;
} H S Rana (UPES)

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Allocating Arrays

We can allocate arrays using new operator.

H S Rana (UPES)


October 3, 2012

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Allocating Arrays

We can allocate arrays using new operator.
General form
p_var = new array_type [size];
size speciﬁes the number of elements in the array.
To free an array, use delete
delete [ ] p_var;

H S Rana (UPES)


October 3, 2012

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Allocating Arrays
Example
#include <iostream>
#include <new>
int main()
{
int *p, i;
try {
p = new int [10]; // allocate 10 integer array
return 1;
}
for(i=0; i<10; i++ )
p[i] = i;
for(i=0; i<10; i++)
cout << p[i] << " ";
delete (UPES) p; // releaseConstructor array
the and Destructor
H S Rana []
October 3, 2012

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Allocating Objects
We can allocate object using new operator.When we do this, an object is created
and a pointer is returned to it.

H S Rana (UPES)


October 3, 2012

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Allocating Objects
We can allocate object using new operator.When we do this, an object is created
and a pointer is returned to it.
Example
#include <iostream>
#include <new>
#include <cstring>
class balance {
double cur_bal;
char name[80];
public:
void set(double n, char *s) {
cur_bal = n;
strcpy(name, s);}
void get_bal(double &n, char *s) {
n = cur_bal;
strcpy(s, name);}};
H S Rana (UPES)


October 3, 2012

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Allocating Objects

H S Rana (UPES)


October 3, 2012

20 / 23


Allocating Objects
Example
int main(){
balance *p; char s[80];
double n;
try {
p = new balance;
return 1;}
p->set(12387.87, "Rahul Kumar");
p->get_bal(n, s);
cout << s << "’s balance is: " << n;
cout << "n";
delete p;
return 0;}
H S Rana (UPES)


October 3, 2012

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Allocating Objects
dynamically allocated objects may have constructors and destructors

H S Rana (UPES)


October 3, 2012

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Allocating Objects
dynamically allocated objects may have constructors and destructors
Example
class balance {
double cur_bal;
char name[80];
public:
balance(double n, char *s) {
cur_bal = n;
strcpy(name, s);
}
~balance() {
cout << "Destructing ";
cout << name << "n";
}
void get_bal(double &n, char *s) {
n = cur_bal;
strcpy(s, name);}
H S Rana (UPES)
};

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Allocating Objects

H S Rana (UPES)


October 3, 2012

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Allocating Objects
Example
int main()
{
balance *p;
char s[80];
double n;
// this version uses an initializer
try {
p = new balance (12387.87, "Rahul Kumar");
return 1;
}
p->get_bal(n, s);
cout << s << "’s balance is: " << n;
cout << "n";
delete p;
returnH S0; (UPES)
Rana

October 3, 2012

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Const Argument

An argument of a function can be declared as const.

H S Rana (UPES)


October 3, 2012

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Const Argument

An argument of a function can be declared as const.
Example
int strlrn(const char *p)
int length(const String &s)
The qualiﬁer const tell the compiler that the function should not modify the
argument. Compiler will generate the error when this condition is violated.

H S Rana (UPES)


October 3, 2012

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Dynamics allocation

Dynamics allocation

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