Boost: polymorphic_cast usage

 

Boost: polymorphic_cast is used to implement down cast. If the conversion fails, an exception is thrown.

 

This is similar to dynamic_cast. However, if the dynamic_cast pointer fails to be converted, no exception is thrown.

 

The following is an example of the two:

 

 

# Ifndef base_for_cast

# Define base_for_cast

 

# Include <iostream>

# Include <boost/cast. HPP>

# Include <boost/scoped_ptr.hpp>

 

Class base1

{

Public:

Virtual void print ()

{

STD: cout <"base1: Print" <STD: Endl;

}

 

Virtual ~ Base1 (){}

Protected:

PRIVATE:

};

 

 

Class base2

{

Public:

Void only_base2 ()

{

STD: cout <"only base2" <STD: Endl;

}

 

Virtual ~ Base2 (){}

Protected:

PRIVATE:

};

 

 

Class derived: Public base1, public base2

{

Public:

Void print ()

{

STD: cout <"derived: Print" <STD: Endl;

}

 

Void only_here ()

{

STD: cout <"only derived 2" <STD: Endl;

}

 

Void only_base2 ()

{

STD: cout <"derived base2" <STD: Endl;

}

~ Derived () {STD: cout <"derived destuctor" <STD: Endl ;}

};

 

Void test_polymorphic_cast ()

{

Base1 * P1 = new derived;

 

Boost: scoped_ptr <base1> BSP (P1 );

P1-> Print ();

 

Try

{

Derived * Pd = boost: polymorphic_cast <derived *> (P1 );

Pd-> only_base2 ();

Pd-> only_here ();

 

Base2 * PBS = boost: polymorphic_cast <base2 *> (P1 );

PBS-> only_base2 ();

}

Catch (STD: bad_cast & E)

{

STD: cout <E. What () <STD: Endl;

}

}

 

Void polyporphic_cast_example (base1 * P)

{

Derived * D = boost: polymorphic_cast <derived *> (P );

D-> Print ();

 

Base2 * b2 = boost: polymorphic_cast <base2 *> (P );

B2-> only_base2 ();

}

 

The above code is compiled and tested through vs2008. Note that the boost library path is set.