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Type Casting in C++ (static, dynamic, reinterpret & const_cast)


Four type of casting operators in C++ are listed below

  • static_cast [convert non polymorphic types]
  • const_cast [add or remove the const-ness or volatile-ness type]
  • dynamic_cast [convert polymorphic types]
  • reinterpret_cast [type conversion of unrelated types]

Example of static_cast

#include <iostream.h>
#include <stdlib.h>

int main()
{
 int sum = 1000;
 int count = 21;
 double average1 = sum/count;
 cout<<"Before conversion = "<<average1<<endl;
 double average2 = static_cast<double>(sum)/count;
 cout<<"After conversion = "<<average2<<endl;
 system("pause");
 return 0;
}

Example of const_cast

//demonstrates const_cast
#include <iostream.h>
#include <stdlib.h>

int main()
{
/* p = 10 is a constant value, 
cannot be modified*/

const int p = 20;
cout<<"const p = ";
cout<<p;
cout<<"\nq = p + 20 = ";
cout<<(p + 20)<<endl;

/*The following code should generate error,
because we try to modify the constant 
value... uncomment, recompile and re run,
notice the error...
p = 15;
p++;
remove the const...
*/

int r = const_cast<int&> (p);

/*the value of 10 should be 
modified now...*/

--r;

//Removing the const, decrement by 1
cout<<"\nNew value = "<<r<<endl;
system("pause");
}

Example of Dynamic cast

//upcast conversion using dynamic_cast

#include <iostream.h>
#include <stdlib.h>

//base class
class Base1 {};

//derived class...
class Derived1:public Base1 {};

//another derived class
class Derived2:public Derived1{};

//dynamic_cast test function...
void funct1()
{
//instantiate an object…
Derived2* Test1 = new Derived2;

/*
upcasting, from derived class to base class,
Derived1 is a direct from Base1
making Test2 pointing to Derived1 sub-object of Test1
*/

Derived1* Test2 = dynamic_cast<Derived1*>(Test1);
cout<<"Derived1* Test2 = 
dynamic_cast<Derived1*>(Test1);"<<endl;

if(!Test2)
cout<<"The conversion is fail..."<<endl;
else
cout<<"The conversion is successful..."<<endl;

//upcasting, from derived class to base class
//Derived2 is an indirect from Base1
Base1* Test3 = dynamic_cast<Derived1*>(Test1);
cout<<"\nBase1* Test3 = 
dynamic_cast<Derived1*>(Test1);"<<endl;

if(!Test3)
cout<<"The conversion is fail..."<<endl;
else
cout<<"The conversion is successful..."<<endl;
}

int main()
{
 funct1();
 system("pause");
 return 0;
}

Example of reinterpret_cast

//unsigned int pointers conversion 

#include <iostream.h> 
#include <stdlib.h> 
unsigned int* Test(int *q) 
{ 
//convert int pointer to unsigned int pointer 
unsigned int* code=reinterpret_cast<unsigned int*>(q); 

/*
return the converted type data, 
a pointer... 
*/
return code; 
}

int main(void) 
{
//array name is a pointer...
int a[10];
cout<<"int pointer unsigned int pointer";

for(int i = 0;i<=10;i++)
cout<<(a+i)<<" converted to:"; 

cout<<Test(a+i); 
system("pause"); 
return 0; 
}