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2010-05-25T14:21:17Z

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2010-05-25T10:29:22Z

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==Incrementing and decrementing an object pointer==

<source lang="cpp">#include <iostream>
using namespace std;

class MyClass {
int x;
public:
void setX(int val) { x = val; }
void display(){ cout << x << "\n"; }
};

int main()
{
MyClass ob[2], *p;

ob[0].setX(10); // access objects directly
ob[1].setX(20);

p = &ob[0]; // obtain pointer to first element
p->display(); // show value of ob[0] using pointer

p++; // advance to next object
p->display(); // show value of ob[1] using pointer

p--; // retreat to previous object
p->display(); // again show value of ob[0]

return 0;
}</source>
<pre class=codeResult>10
20
10</pre>

==normal functions accessed from pointer==

<source lang="cpp">#include <iostream>
using namespace std;
class Base{
public:
void show(){ cout << "Base\n"; }
};
class Derv1 : public Base{
public:
void show(){ cout << "Derv1\n"; }
};
class Derv2 : public Base{
public:
void show(){ cout << "Derv2\n"; }
};
int main(){
Derv1 dv1;
Derv2 dv2;
Base* ptr;

ptr = &dv1;
ptr->show();

ptr = &dv2;
ptr->show();
return 0;
}</source>

==Passing References to Objects==

<source lang="cpp">#include <iostream>
using namespace std;

class MyClass {
int id;
public:
int i;
MyClass(int i);
~MyClass();
void neg(MyClass &o) { o.i = -o.i; } // no temporary created
};

MyClass::MyClass(int num)
{
cout << "Constructing " << num << "\n";
id = num;
}

MyClass::~MyClass()
{
cout << "Destructing " << id << "\n";
}

int main()
{
MyClass o(1);

o.i = 10;
o.neg(o);

cout << o.i << "\n";

return 0;
}</source>

==Pointers as data members==

<source lang="cpp">#include <iostream>

class MyClass
{
public:
MyClass();
~MyClass();
int GetAge() const { return *itsAge; }
void SetAge(int age) { *itsAge = age; }

int GetWeight() const { return *itsWeight; }
void setWeight (int weight) { *itsWeight = weight; }

private:
int * itsAge;
int * itsWeight;
};

MyClass::MyClass()
{
itsAge = new int(2);
itsWeight = new int(5);
}

MyClass::~MyClass()
{
delete itsAge;
delete itsWeight;
}

int main()
{
MyClass *objectPointer = new MyClass;
std::cout << "objectPointer is " << objectPointer->GetAge() << " years old\n";

objectPointer->SetAge(5);
std::cout << "objectPointer is " << objectPointer->GetAge() << " years old\n";

delete objectPointer;
return 0;
}</source>
<pre class=codeResult>objectPointer is 2 years old
objectPointer is 5 years old</pre>

==Pointers to Class Members==

<source lang="cpp">#include <iostream>
using namespace std;

class MyClass {
public:
MyClass(int i) { val=i; }
int val;
int double_val() { return val+val; }
};

int main()
{
int MyClass::*data; // data member pointer
int (MyClass::*func)(); // function member pointer
MyClass ob1(1), ob2(2); // create objects

data = &MyClass::val; // get offset of val
func = &MyClass::double_val; // get offset of double_val()

cout << "Here are values: ";
cout << ob1.*data << " " << ob2.*data << "\n";

cout << "Here they are doubled: ";
cout << (ob1.*func)() << " ";
cout << (ob2.*func)() << "\n";

return 0;
}</source>

==Sort person objects using array of pointers==

<source lang="cpp">#include <iostream>
#include <string>
using namespace std;
class person{
protected:
string name;
public:
void setName()
{ cout << "Enter name: "; cin >> name; }
void printName()
{ cout << endl << name; }
string getName()
{ return name; }
};
int main(){
void bsort(person**, int);
person* persPtr[100];
int n = 0;
char choice;

do {
persPtr[n] = new person;
persPtr[n]->setName();
n++;
cout << "Enter another (y/n)? ";
cin >> choice;
}while( choice=="y" );

cout << "\nUnsorted list:";
for(int j=0; j<n; j++)
{
persPtr[j]->printName();
}

bsort(persPtr, n);

cout << "\nSorted list:";
for(int j=0; j<n; j++)
{
persPtr[j]->printName();
}
cout << endl;
return 0;
}
void bsort(person** pp, int n){
void order(person**, person**);
int j, k;

for(j=0; j<n-1; j++)
for(k=j+1; k<n; k++)
order(pp+j, pp+k);
}
void order(person** pp1, person** pp2){
if( (*pp1)->getName() > (*pp2)->getName() ) {
person* tempptr = *pp1;
*pp1 = *pp2;
*pp2 = tempptr;
}
}</source>

==To use a pointer to the object, you need to use the ->* operator==

<source lang="cpp">#include <iostream>
using namespace std;

class MyClass {
public:
MyClass(int i) { val=i; }
int val;
int double_val() { return val+val; }
};

int main()
{
int MyClass::*data; // data member pointer
int (MyClass::*func)(); // function member pointer
MyClass ob1(1), ob2(2); // create objects
MyClass *p1, *p2;

p1 = &ob1; // access objects through a pointer
p2 = &ob2;

data = &MyClass::val; // get offset of val
func = &MyClass::double_val; // get offset of double_val()

cout << "Here are values: ";
cout << p1->*data << " " << p2->*data << "\n";

cout << "Here they are doubled: ";
cout << (p1->*func)() << " ";
cout << (p2->*func)() << "\n";

return 0;
}</source>

==Use class pointer and class array together==

<source lang="cpp">#include "iostream.h"
class MyClass
{
private:
int Price;
int Count;
long Total;
public:
void Input(int P,int C)
{
Price=P;
Count=C;
}
void MyClass::Compute()
{
Total=(long) Price*Count;
}
void MyClass::Print(){
cout<<"Price="<<Price<<" Count="<<Count <<" Total="<<Total<<"\n";
}
};
int main()
{
MyClass *ob;

ob=new MyClass[6];
ob[0].Input(5,0);
ob[1].Input(3,5);
ob[2].Input(1,0);
ob[3].Input(5,20);
ob[4].Input(4,0);
ob[5].Input(8,5);

for(int i=0;i<6;i++)
ob[i].Compute();
for(int i=0;i<6;i++)
ob[i].Print();

delete ob;
}</source>
<pre class=codeResult>Price=5 Count=0 Total=0
Price=3 Count=5 Total=15
Price=1 Count=0 Total=0
Price=5 Count=20 Total=100
Price=4 Count=0 Total=0
Price=8 Count=5 Total=40</pre>

==Use new to allocate memory for a class pointer==

<source lang="cpp">#include<iostream.h>
#include<string.h>
class phone
{
char name[50];
char tell[15];
public:
void store(char *n,char *num);
void print();
};
void phone::store(char *n,char *num)
{
strcpy(name,n);
strcpy(tell,num);
}
void phone::print()
{
cout<<name<<":"<<tell;
cout<<"\n";
}
main()
{
phone *p;
p=new phone;
if(!p)
{
cout<<"Alloction error.";
return 1;
}
p->store("AA","9999999999");
p->print();
delete p;
return 0;
}</source>
<pre class=codeResult>AA:9999999999</pre>

==Use & to get object address==

<source lang="cpp">#include <iostream>

class MyClass
{
public:
MyClass();
MyClass(MyClass&);
~MyClass();

int GetAge() const { return itsAge; }
void SetAge(int age) { itsAge = age; }

private:
int itsAge;
};

MyClass::MyClass()
{
std::cout << "Constructor...\n";
itsAge = 1;
}

MyClass::MyClass(MyClass&)
{
std::cout << "Copy Constructor...\n";
}

MyClass::~MyClass()
{
std::cout << "Destructor...\n";
}

const MyClass * const
FunctionTwo (const MyClass * const obj);

int main()
{
MyClass myObject;
std::cout << "myObject is ";
std::cout << myObject.GetAge() << " years old\n";
int age = 5;
myObject.SetAge(age);
std::cout << "myObject is ";
std::cout << myObject.GetAge() << " years old\n";
std::cout << "Calling FunctionTwo...\n";
FunctionTwo(&myObject);
std::cout << "myObject is ";
std::cout << myObject.GetAge() << " years old\n";
return 0;
}

const MyClass * const FunctionTwo (const MyClass * const obj)
{
std::cout << "Function Two. Returning...\n";
std::cout << "myObject is now " << obj->GetAge();
std::cout << " years old \n";
return obj;
}</source>
<pre class=codeResult>Constructor...
myObject is 1 years old
myObject is 5 years old
Calling FunctionTwo...
Function Two. Returning...
myObject is now 5 years old
myObject is 5 years old
Destructor...</pre>

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