Curs 3

Question 1

class MyClass
{
int x;
public:
MyClass(int value) { this->x = value; }
};
class Date
{
MyClass m;
public:
Date() { }
};
void main()
{
Date d;
}

Answer 1

slide 25
error C2512: ‘MyClass’: no appropriate default
constructor available

Question 2

class MyClass
{
int x;
public:
MyClass(int value) { this->x = value; }
};
class Date
{
MyClass m;
public:
Date() : m(123) { }
};
void main()
{
Date d;
}

Answer 2

slide 26
This code will compile properly

Question 3

class MyClass
{
int x;
public:
MyClass(int value) { this->x = value; }
};
class Date
{
MyClass m;
public:
Date() : m(123) { }
Date(int value) { }
};
void main()
{
Date d;
}

Answer 3

slide 27
error C2512: ‘MyClass’: no appropriate default
constructor available
This code will NOT compile. There is at least one constructor that does not
instantiate data member “m” from class Date.

Question 4

class MyClass
{
int x;
public:
MyClass(int value) { this->x = value; }
};
class Date
{
MyClass m;
public:
Date() : m(123) { }
Date(int value) : m(value+10) { }
};
void main()
{
Date d;
}

Answer 4

the code compiles correctly

Question 5

class MyClass
{
int x;
public:
MyClass(int value) { this->x = value; }
MyClass() { this->x = 0; }
};
class Date
{
MyClass m;
public:
Date() { }
Date(int value) : m(value+10) { }
};

Answer 5

slide 29
This code compiles correctly.

Question 6

class MyClass
{
int x;
public:
};
class Date
{
MyClass m;
public:
Date() { }
Date(int value) { }
};

Answer 6

slide 30
This code compiles correctly

Question 7

class MyClass
{
int x;
public:
MyClass(int value) { this->x = value; }
MyClass() { this->x = 0; }
};
class Date
{
MyClass m = { 123 };
public:
Date() { }
Date(int value) { }
};

Answer 7

slide 31
yes

Question 8

class MyClass
{
int x;
public:
MyClass(int value) { this->x = value; }
MyClass() { this->x = 0; }
};
class Date
{
MyClass m = 123;
public:
Date() { }
Date(int value) { }
};

Answer 8

slide 31
yes

Question 9

class Tree {
public:
Tree(const char * name) { printf(“Tree: %s\n”, name); }
};
class Car {
public:
Car(const char * name) { printf(“Car: %s\n”, name); }
};
class Animal {
public:
Animal(const char * name) { printf(“Animal: %s\n”, name); }
};
class Object
{
Tree t;
Car c;
Animal a;
public:
};
void main() {
Object obj;
}

Answer 9

slide 32
This code will not compile because data members obj.t , obj.c and obj.a need a
custom call to their own constructor.

Question 10

class Tree {
public:
Tree(const char * name) { printf(“Tree: %s\n”, name); }
};
class Car {
public:
Car(const char * name) { printf(“Car: %s\n”, name); }
};
class Animal {
public:
Animal(const char * name) { printf(“Animal: %s\n”, name); }
};
class Object
{
Tree t;
Car c;
Animal a;
public:
Object(): t(“oak”), a(“fox”), c(“Toyota”) {}
};
void main() {
Object obj;
}

Answer 10

slide 33
Output:
Tree: oak
Car: Toyota
Animal: fox

Question 11

class Tree {
public:
Tree() { printf(“CTOR: Tree\n”); }
};
class Car {
public:
Car() { printf(“CTOR: Car\n”); }
};
class Animal {
public:
Animal() { printf(“CTOR: Animal\n”); }
};
class Object
{
Tree t1,t2;
Car c;
Animal a;
};
void main() {
Object obj;
}

Answer 11

slide 34
Output:
CTOR: Tree
CTOR: Tree
CTOR: Car
CTOR: Animal

Question 12

class Object
{
int x, y, z;
public:
Object(int value) : x(value), y(xx), z(valuey) {}
};
void main()
{
Object o(10);
}

Answer 12

slide 35
o.x = 10 (the first one to be computed)
❑ o.y = o.x * o.x = 10 * 10 = 100 (the second one to be computed)
❑ o.z = 10 * o.y = 10 * 100 = 1000 (the third one to be computed)

Question 13

class Object
{
int x, y, z;
public:
Object(int value) : y(value), z(value/2), x(y*z) {}
};
void main()
{
Object o(10);
}

Answer 13

slide 36
o.x = o.y * o.z = unknown results (it depends on the values that resides on the stack when
the instance “o” is created). (the first one to be computed !)
❑ o.y = 10 (the second one to be computed)
❑ o.z = 10 (value) / 2= 10 / 2 = 5 (the third one to be computed)

Question 14

class Date
{
private:
int x;
const int y;
public:
};
void main()
{
Date d;
}

Answer 14

slide 38
const int y nu e initializat

Question 15

class Date
{
private:
int x;
int & y;
public:
};
void main()
{
Date d;
}

Answer 15

slide 38
int & y nu e initializat

Question 16

class Date
{
private:
int x;
const int y;
public:
Date();
};
Date::Date() : x(100), y(123)
{
}
void main()
{
Date d;
}

Answer 16

slide 40
The code compiles – y is initialized with value 123 in example

Question 17

class Date
{
private:
int x;
int & y;
public:
Date();
};
Date::Date() : x(100), y(x)
{
}
void main()
{
Date d;
}

Answer 17

slide 40
yes

Question 18

class Date
{
private:
int x;
const int y;
public:
Date();
Date(int value);
};
Date::Date() : x(100), y(123)
{
}
Date::Date(int value) : x(value)
{
}

Answer 18

slide 41
no

Question 19

class Date
{
private:
int x;
int & y;
public:
Date();
Date(int value);
};
Date::Date() : x(100), y(x)
{
}
Date::Date(int value) : x(value)
{
}

Answer 19

slide 41
no

Question 20

class Date
{
private:
int x;
const int y;
public:
Date();
Date(int value);
};
Date::Date() : x(100), y(123)
{
}
Date::Date(int value) : x(value), y(value*value)
{
}
void main()
{
Date d;
D

Answer 20

slide 42
yes

Question 21

class Date
{
private:
int x;
const int y;
public:
Date();
};
Date::Date() : x(100)
{
y = 123;
}
void main()
{
Date d;
}

Answer 21

slide 43
no

Question 22

class Date
{
private:
int x;
int & y;
public:
Date();
};
Date::Date() : x(100)
{
y = x;
}
void main()
{
Date d;
}

Answer 22

slide 43
no

Question 23

class Date
{
private:
int x;
const int y = 123;
public:
Date();
Date(int value);
};
Date::Date() : x(100)
{
}
Date::Date(int value) : x(value), y(value*value)
{
}
void main()
{
Date d;
Date d2(100);
}

Answer 23

Slide 44
This code compiles correctly

Question 24

class Date
{
private:
int x;
int & y = x;
public:
Date();
Date(int value);
};
Date::Date() : x(100)
{
}
Date::Date(int value) : x(value), y(value)
{
}
void main()
{
Date d;
Date d2(100);
}

Answer 24

slide 44
This code compiles correctly

Question 25

class Date
{
int & y;
public:
Date() : y(123) {}
};
void main()
{
Date d;
}

Answer 25

slide 45
eroare
References that are not constant can not be instantiated with a constant
value

Question 26

class Date
{
const int & y;
public:
Date() : y(123) {}
};
void main()
{
Date d;
}

Answer 26

slide 45
yes

Question 27

class Date
{
public:
const int & y;
Date() : y(123) {}
void Test() {
int a[1000];
for (int tr = 0; tr < 1000; tr++)
a[tr] = 50;
}
};
void main()
{
Date d;
printf(“%d\n”,d.y);
d.Test();
printf(“%d\n”,d.y);
}

Answer 27

slide 49
Output:
123
50
s-a suprascris stackul

Question 28

class Object
{
int x, y;
public:
Object(int value) : x(value), y(value) {}
Object() : Object(0) , y(1) { }
};
void main()
{
Object o;
}

Answer 28

slide 52
This code will not compile. When calling a constructor from another
constructor initialization list, other initializations are not possible

Question 29

class Object
{
int x, y;
public:
Object(int value) : x(value), y(value) {}
Object() : Object(0) { y = 1; }
};
void main()
{
Object o;
}

Answer 29

slide 54
This code will compile.

Question 30

class Object
{
int x, y;
const int z;
public:
Object(int value) : x(value), y(value), z(value) {}
Object() : Object(0) { y = 1; }
};
void main()
{
Object o;
}

Answer 30

slide 57
yes

Question 31

class Data
{
public:
int x;
char t;
const char* m;
};
void main()
{
Data d1{ 10, ‘A’, “test” };
Data d2 = { 5, ‘B’, “C++” };
Data array[] = {
{ 1, ‘A’, “First element” },
{ 2, ‘B’, “Second element” },
{ 3, ‘C’, “Third element” },
};
}

Answer 31

slide 62
This code works, but it is important for data members to be public

Question 32

class Data
{
int x;
public:
char t;
const char* m;
};
void main()
{
Data d1{ 10, ‘A’, “test” };
Data d2 = { 5, ‘B’, “C++” };
Data array[] = {
{ 1, ‘A’, “First element” },
{ 2, ‘B’, “Second element” },
{ 3, ‘C’, “Third element” },
};
}

Answer 32

slide 63
This code will not work as “x” is not public ! If a class has at least one member
that is NOT public and no matching constructor, these assignments will not be
possible.

Question 33

class Data
{
int x;
public:
char t;
const char* m;
Data(int xx, char tt, const char * mm) : x(xx), t(tt), m(mm) {};
};
void main()
{
Data d1{ 10, ‘A’, “test” };
Data d2 = { 5, ‘B’, “C++” };
Data array[] = {
{ 1, ‘A’, “First element” },
{ 2, ‘B’, “Second element” },
{ 3, ‘C’, “Third element” },
};
}

Answer 33

slide 64
This code will compile because a proper public constructor has been added.

Question 34

class Data
{
public:
int x;
char t;
const char* m;
Data(int xx, char tt) : x(xx), t(tt), m(nullptr) {};
};
void main()
{
Data d1{ 10, ‘A’, “test” };
Data d2 = { 5, ‘B’, “C++” };
Data array[] = {
{ 1, ‘A’, “First element” },
{ 2, ‘B’, “Second element” },
{ 3, ‘C’, “Third element” },
};
}

Answer 34

slide 65
This code will not compile. If there at least one constructor and its
parameters do NOT match the ones from the initialization list, the compiler
will throw an error

Question 35

class Data
{
int x;
public:
char t;
const char* m;
Data(int xx, int tt, const void * p) : x(xx), t(tt), m((const char *)p) {};
};
void main()
{
Data d1{ true, ‘A’, “test” };
Data d2 = { true, ‘A’, “test” };
}

Answer 35

slide 66
yes

Question 36

class Data
{
int x;
public:
char t;
const char* m;
Data(…) {};
};
void main()
{
Data d1{ true, ‘A’, “test” };
Data d2 = { true, ‘A’, “test” };
}

Answer 36

slide 67
yes

Question 37

class Data
{
int x;
public:
char t;
const char* m;
Data(int xx, int tt, const void * p) : x(xx), t(tt), m((const char *)p) {};
};
void main()
{
Data d1{};
Data d2 = {};
}

Answer 37

slide 68
This code will NOT compile.
Trying to initialize this class with an empty initialization list { } will result in
an error if no default constructor is present

Question 38

class Data
{
int x;
public:
char t;
const char* m;
Data() {};
};
void main()
{
Data d1{};
Data d2 = {};
}

Answer 38

slide 69
yes

Question 39

class Data
{
int x;
public:
char t;
const char* m;
Data(…) {};
};
void main()
{
Data d1{};
Data d2 = {};
}

Answer 39

slide 69
yes

Question 40

class Data
{
int x;
public:
char t;
const char* m;
};
void main()
{
Data d1 {};
}

Answer 40

slide 70
This code will compile. “d1” object will have the following values after the
execution:
❑ d1.x = 0
❑ d1.t = ‘\0’
❑ d1.m = nullptr;

Question 41

class Data
{
int x;
public:
Data(int value) : x(value) {}
};
void main()
{
Data d = 10;
}

Answer 41

slide 73
yes

Question 42

class Data
{
int x;
public:
Data(int value) :
x(value) {}
};
void main()
{
Data d = ‘A’;
}

Answer 42

74
yes

Question 43

class Data
{
int x;
public:
Data(int value) :
x(value) {}
};
void main()
{
Data d = true;
}

Answer 43

74
yes

Question 44

class Data
{
int x;
public:
Data(int value) :
x(value) {}
};
void main()
{
Data d = 4.5;
}

Answer 44

74
yes

Question 45

class Data
{
int x[4];
public:
Data() : x{ 1, 2, 3, 4 } {}
};
void main()
{
Data d;
}

Answer 45

75
yes

Question 46

class Data
{
int x = 5;
float y = 10.5f;
bool t = false;
public:
Data() : x(10) { }
};
void main()
{
Data d;
}

Answer 46

80
the default values can be overridden in the constructor list. In
this case, “x” will be initialized with 10, “y” with 10.5 and “t” with false

Question 47

class Date
{
int x;
public:
Date(const Date &d) { x = d.x; }
Date(Date &d) { x = d.x * 2; }
Date(int v) { x = v; }
};
int main()
{
const Date d(1);
Date d2 = d;
return 0;
}

Answer 47

100
yes

Question 48

class Date
{
int x;
public:
Date(Date &d) { x = d.x * 2; }
Date(int v) { x = v; }
};
int main()
{
const Date d(1);
Date d2 = d;
return 0;
}

Answer 48

101
eroare
In this case the code will not compile. There a copy constructor defined, but
it does not accept const parameters

Question 49

class Date
{
int x;
public:
Date(int v) { x = v; }
};
int main()
{
const Date d(1);
Date d2 = d;
return 0;
}

Answer 49

102
This code will compile.
 Since there is no copy constructor defined, the compiler will generate a code
that copies the data from “d” to “d2” (similar to what memcpy function
does).

Question 50

class Object
{
int value;
static Object* instance;
Object() { value = 0; }
public:
static Object* GetInstance() { … }
};
Object* Object::instance = nullptr;
void main()
{
Object obj1;
Object * obj = new Object();
}

Answer 50

116
no
error C2248: ‘Object::Object’: cannot access private
member declared in class ‘Object’
note: see declaration of ‘Object::Object’
note: see declaration of ‘Object’

Question 51

class Object
{
int value;
Object(): value(0) { }
friend class ObjectUser;
};
class ObjectUser
{
public:
int GetValue();
};
int ObjectUser::GetValue()
{
Object o;
return o.value;
}
void main()
{
ObjectUser ou;
printf(“%d\n”, ou.GetValue());
}1

Answer 51

117
yes

Question 52

class Object
{
int value;
Object(): value(0) { }
friend class ObjectUser;
};
class ObjectUser
{
public:
int GetValue();
};
int ObjectUser::GetValue()
{
Object o;
return o.value;
}
void main()
{
Object obj;
}

Answer 52

118
This code will NOT compile
error C2248: ‘Object::Object’: cannot access private member
declared in class ‘Object’
note: see declaration of ‘Object::Object’
note: see declaration of ‘Object’

Question 53

class Date
{
int value;
public:
Date(int x) { value = x; }
};
int main()
{
Date d(‘0’);
return 0;
}

Answer 53

122
This code works, due to promotion mechanism (‘a’ (a char) is promoted to an
int).

Question 54

class Date
{
int value;
public:
Date(char x) = delete;
Date(int x) { value = x; }
};
int main()
{
Date d(‘0’);
return 0;
}

Answer 54

123
This code will not compile.
 Using the delete keyword in this manner tells the compiler that there is a
constructor that has a char parameter, but it can not be used !

Question 55

class Date
{
int value;
public:
explicit Date(int v1, int v2, int v3) { value = v1+v2+v3; }
};
int main()
{
Date d = { 1, 2, 3 };
return 0;
}

Answer 55

126
explicit
error C3445: copy-list-initialization of ‘Date’ cannot use an
explicit constructor
note: see declaration of ‘Date::Date’