Basic C++

Question 1

Mutable

Answer 1

Allow update non <test> static member from const function</test>

Question 2

Compiler constant trick

Answer 2

Enum enum { dimension = 10}

double array[dimension];

Question 3

Explicit Inlining

Answer 3

Class Test {

Inline void setdate();

};

void Test::setdate() { ….. }

Question 4

Why function style cast

Answer 4

Optimize constructor call when return an object by function by value.

Complex getComplexnumber() {

return Complex( real, image)

}

Question 5

Array initialization

Answer 5

int array[3] = {1,2,3}

Question 6

Placement new

Answer 6

Syntax T *ptr = new (/* address */) T ( optional args )

Question 7

inheritance: Access Privileges Public, Protected and private

Answer 7

if Public on derived class everything is the same, if Protected then Public of base class will be protected, if private then Public and protected of base class will be private

Question 8

How to change inherited access for some function of base class?

Answer 8

By keyword “using :: under Public: or Protected: or Private:

Question 9

inheritance: Function Hiding

Answer 9

if derived class has the same function name then that function no longer access on base class. We can use “using ::; to make it available. or you can explicit specify ::

Question 10

what function never inherited by derived class

Answer 10

Constructor, destructor and assignment operator

Question 11

what is upcast and sliced off in term of Derived-to-Base class

Answer 11

upcast is casting pointer of derived class to base class sliced off is create base class by derived class

Question 12

why do we need virtual function?

Answer 12

to able to have pointer of base class but the actual call will call derived class function.

Note: If derived class object call base class function and inside base class function call function that have the same name as base and derived then the function on base class will be called if it is not virtual function.

Ex:

class dog {

void bark() { cout << “I’m dog”; }

void seesomething() { bark(); }

}

class yellowdog : public dog {

void bark() { cout << “I’m yellow dog”; }

}

function bark should be virtual function

Question 13

why destructor should declare as virtual function

Answer 13

to make sure that derived class destructor wiil get called.

Question 14

Can we less restrict exception specification in virtual function?

Answer 14

No.

Question 15

why use virtual in part of derivation process?

Answer 15

to solve problem of two subclass of class has common class (diamond problem). For instance, base class “Appliance” is derived by “AlarmClock” also derived by “Radio”. And class “AlarmClockRadio” derived both “Radio” and “AlarmClock”. We want to create only one base class “Appliance”

Question 16

How to choose to call base class constructor?

Answer 16

Write base class name followed by a parenthetical list of arguments to be passed to constructor.

Question 17

to use “atol”, what is include file?

Answer 17

Question 18

is this program call copy constructor of MyClass?

MyClass a, b;

a = b;

Answer 18

No This program will call assignment operator on a=b.

Question 19

Is copy constructor called or assignment operator called from the following snippet code:

MyClass a;

Const MyClass b = a;

Answer 19

Copy constructor is called because: Copy constructor is called when a new object is created from an existing object, as a copy of the existing object

Question 20

What is Conversion Operator

Answer 20

We can also write conversion operators that can be used to convert one type to another type.

Question 21

What will happen?

Test *ptr = new Test;

Answer 21

There are actually two things that happen in the above statement–memory allocation and object construction; the new keyword is responsible for both. One step in the process is to call operator new in order to allocate memory; the other step is to actually invoke the constructor. Operator new only allows us to change the memory allocation method, but does not do anything with the constructor calling method. Keyword new is responsible for calling the constructor, not operator new.

Question 22

How can overload operator?

Answer 22

It is started by “operator” keyword then by symbol of operator.

int operator+(int y); // t+y means t.operator+(y)

We can use operator to convert object to other type

operator string() const { return to_string(a); }

Question 23

What is global operator and why do we need it?

Answer 23

If that operator is not the memeber of that class then we need to create friend class in that object to support that operator.

Ex: operator “<<”, we want ostream to work with our object with ostream. ostream class is in the left side (cout << myobj; // cout.operator<<(myobj)).

We can’t change ostream class then we have to add global operator in our class then it will work with ostream.

friend ostream& operator<<(ostream &out, myclass) { ???; return out;}

Question 24

When to use static_cast

Answer 24

• to convert object from one type to another, operator type conversion need to be defined
• convert pointer/reference from one type to related type

Question 25

When to use dynamic_cast

Answer 25

convert base class to derieved class

Note: need to have at least one virtual function

Question 26

When to use reinterpret_cast

Answer 26

to cast address value to object.

Ex: long p = 510000;

Dog *p = reinterpret_cast&ampDog *&amp(p)

Question 27

How to cast shared_ptr?

Answer 27

static_pointer_cast

dynamic_pointer_cast

const_pointer_cast

Question 28

Date time functions in C++

Answer 28

time_t cur_time;

cur_time = chrono::system_clock::to_time_t(chrono::system_clock::now());

struct tm _tm;

char buffer[80];

localtime_r(&cur_time, &_tm);

strftime(buffer, 80, “%Y/%m/%d”, &_tm);