C++ Tutorial/Class/object pointer
Содержание
- 1 Incrementing and decrementing an object pointer
- 2 normal functions accessed from pointer
- 3 Passing References to Objects
- 4 Pointers as data members
- 5 Pointers to Class Members
- 6 Sort person objects using array of pointers
- 7 To use a pointer to the object, you need to use the ->* operator
- 8 Use class pointer and class array together
- 9 Use new to allocate memory for a class pointer
- 10 Use & to get object address
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>
10 20 10
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>
objectPointer is 2 years old objectPointer is 5 years old
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>
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
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>
AA:9999999999
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>
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...
