Friend classes Friend class methods Nested classes Throwing exceptions, try blocks and catch blocks Exception classes Runtime type identification (RTTI)

• Friend classes• Friend class methods• Nested classes• Throwing exceptions, try blocks and

catch blocks• Exception classes• Runtime type identification (RTTI)• dynamic_cast and typeid• static_cast, const_cast, and

reinterpret_cast

Friend, Exceptions, and More

Friends

• Friend function– Allow to access the private and protected

members of the original class• Friend class

– Every member function in the friend class are allowed to access both private and protected members of the original class

Friend class

• TV and Remote– On/off– Channel setting – Volume setting– Antenna or cable tuning mode– TV tuner or A/V input

• Program tv.h, tv.cpp, use_tv.cpp

Friend member functions

Friend relationships

• Program tvfm.h

Interactive remote controller

Shared friends

• Probe class– Programmable measuring device

• Analyzer class– Programmable analyzing device

• Each has an internal clock and one would like to be able to synchronize the two clocks

Shared friends

Nested classesSuppose queue class declaration:

Methods definitions

More appropriate declaration

Using constructor to rewrite

This makes the code for enqueuer() a bit shorter and a bit safer because it automates initialization rather than requiring the programmer to correctly remember what should be done

Nested classes and access

• Nested class is different from containment• A nested class is declared controls the scope

of the nested class. It establishes which parts of a program can create objects of that class

• Nested class object can be used in class A• As with an class, the public, protected, and

private sections of a nested class provide access control to class members

Scope properties for nested classes

二類別

• Program queuetp.h, nested.cpp

Exceptions

• Standard error stream– abort(); // cstdlib.h, doesn’t clear buffer– cerr(); // standard error stream– exit(); // clear buffer, but no messages

• Program error1.cpp, error2.cpp

The exception mechanism• Three components

– Throwing an exception (throw)– Catching an exception with a handler

(catch)– Using a try block (try)

• Program error3.cpp

Program flow with exceptions

Using objects as exceptions

• Program exc_mean.h, error4.cpp

Unwinding the stack

• Program error5.cpp

More exception features

catch (…)

The exception class

The stdexcept exception class

• Classes logic_error, runtime_error derived publicly from exception

• Classes domain_error, invalid_argument, length_error, out_of_bounds derived publicly from logic_error

• Classes range_error, overflow_error, underflow_error derived publicly from runtime_error

The logic_error class

The bad_alloc exception and new

• Class bad_alloc derived publicly from exception class

• Program newexcp.cpp• The null pointer and new

Exceptions, classes, and inheritance

• One can derive one exception class from another

• One can incoporate exceptions into classes by nesting exception class declarations inside a class definition

• Such nested declarations can be inherited and can serve as base classes themselves

• Program sales.h, sales.cpp, use_sales.cpp

Runtime type identification (RTTI)

• RTTI is one of more recent additions to C++, which is not supported by many older implementations

• How can one tells what kind of object a base-class pointer points to? – Find the correct non-virtual functions in

class– For the reasons of debugging

How does RTTI work?

• Three components supporting RTTI• dynamic_cast operator

– Generate a derived type from a pointer to a base type; return null pointer (0) when fail

• typeid operator– Return a value identifying the exact type of an

object• type_info structure

– Store information about a particular type

dynamic_cast operator

• Program rtti1.cpp

The typeid operator & type_info class

• #include <typeinfo.h>if (typeid(Magnificent) == typeid(*pg))

…cout << “Now processing type “ <<

typeid(*pg).name() << endl;• Program rtti2.cpp

Misusing RTTI

Rewrite code

Type cast operators

Completing type cast

• dynamic_cast• const_cast• static_cast• reinterpret_cast

dynamic_cast

const_cast

• Program constcast.cpp

static_cast

reinterpret_cast

• The following type cast is allowed in C but not in C++ implementations the char is too small to hold a pointer implementation