מונחה עצמים- תרגול 10 | RTTI and Advanced Exceptions

7/30/2019 RTTI and Advanced Exceptions | - 10

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Object Oriented ProgrammingTirgul 10

Downcasting and RTTI

Advanced Exceptions


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Downcasting and RTTIdowncastingcasting

reference.

:

Derived* d = new Base();

++C.++Cdowncasting

. :RTTI (Real Time Type Information).++C".

.


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Downcasting and RTTIRTTI

.

. ++C3-RTTI:dynamic_casttypeid

type_info


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Downcasting and RTTI

A* p1 = new A();A* p2 = new B();A* p3 = new C();

/*------------------*/C* p4 = (C*) p3;C* p5 = (C*) p1;B* p6 = (B*) p3;

A

B

C

// safe// not safe// safe


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dynamic_cast

B* p6 = dynamic_cast(p1);

-p1*B.,p1.,0(null pointer.)


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dynamic_castclass Pet {public:

virtual ~Pet(){}

};

class Dog : public Pet{};

class Cat : public Pet{};


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dynamic_castint main() {

Pet* b = new Cat();Dog* d1 = dynamic_cast(b);

Cat* d2 = dynamic_cast(b);

cout


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typeid & type_info

typeid2typeid(B) == typeid(*p6);

typeidreference type_info.type_info==!=

typeidtrue/false.

null bad_typeid exception.".

"name()


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class Grand{

int hold;

public:

Grand(int h=0) : hold(h){}virtual void speak() const {cout


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class Magnificent : public Superb {char ch;

public:Magnicifent(int h=0, char c=A): Superb(h), ch(c){}void speak() const { coust


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Grand* getObj {

Grand* p;

switch(rand() % 3) {case 0: p = new Grand(10);break;

case 1: p = new Supberb(20);break;case 2: p = new Magnificent(30,M);break;}

return p;

}


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#include

int main {

srand(time(0));Grand* pg;Superb *ps;

for (int i = 0; i < 5; ++i) {pg = getObj();cout


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int main {

Person person;Employee emp;Person* ptr = &emp;

cout


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exception

what()

-


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class exception {public:

exception () throw();exception (const exception&) throw();

exception& operator= (const exception&) throw();virtual ~exception() throw();virtual const char* what() const throw();

}


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#include #include

using namespace std;

class Polymorphic {

virtual void Member(){}

};

int main () {try{

Polymorphic * pb = 0;typeid(*pb); // throws a bad_typeid exception

} catch (exception& e) {cerr


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exception

bad_alloc

bad_castbad_exception

bad_typeid

runtime_error

range_error overflow_error underflow_error


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bad_alloc"new.

bad_cast"dynamic_cast.

bad_exceptioncatch.

bad_typeid"typeid.

ios_base::failureiostream.


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runtime_error.

.

:

range_error

overflow_erroroverflow.

underflow_errorunderflow .

++C.

std::exception


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#include #include

using namespace std;

int main () {try

{ int* myarray = new int[1000];}catch (bad_alloc& e){

cout


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-Fraction.

,

0...

//Fraction.cpp

class DivideByZeroException : public runtime_error {public:

DivideByZeroException(): runtime_error( "attempted to divide by zero" ) {}

};

const Fraction operator / (const Fraction &f1, const Fraction &f2) {if(f2.m_iNom == 0)

throw(DivideByZeroException());int nn = f1.m_iNom * f2.m_iDenom;int dd = f1.m_iDenom * f2.m_iNom;return Fraction (nn, dd);

}

istream& operator >> (istream &is, Fraction &frac) {char divSign;is >> frac.m_iNom >> divSign >> frac.m_iDenom;if(frac.m_iDenom == 0)

throw(DivideByZeroException());frac.reduce ();return is;

}

int main(){

Fraction f1;bool fracOK = false;while (!fracOK){

try{cin>>f1;fracOK=true;

} catch (runtime_error& err) {cout


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-...

-Constructor!

"

//Fraction.cpp

class DivideByZeroException : public runtime_error {public:

DivideByZeroException(): runtime_error( "attempted to divide by zero" ) {}

};

Fraction::Fraction (int nn, int dd) : m_iNom (nn), m_iDenom (dd) {if(m_iDenom == 0)

throw(DivideByZeroException());reduce ();

}


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new#include

#include #include using namespace std;

void f(){char* pc = newchar[999999999999];//...

}

int main(){try{

f();}catch (bad_alloc& ex){

cerr


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Ctor \ new?

2 ...

bad_allocnew

runtime_error

catch

)!(

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מונחה עצמים- תרגול 10 | RTTI and Advanced Exceptions