Ще го задата по възможно най простиа начин
Object {
public:
Object();
~Object();
};
class SubObject {
public:
SubObject();
~SubObject();
};
SubObject someObject();
delete someObject;
В този случай ще се викнат ли и деструктора на Object и на SubObject, или трябва както с конструкторите да покажеш, че искаш да се пусне и конструктора на горния клас?
ami ne sym мн сиг в това, което ще каже, нека някой по-знаещ да ме поправи. Първо ще се извика конструкторът на класа Обжект, после конструктора на СъбОбжект, после деструктора на Събобйект. Мисля, че деструктор на Обжект няма да се вика, тъй като не унищожаване обект от родителския клас, ама дали е така ???? :)
Аз си се оправих докато ми отговорите но благодаря все пак :)
a oтговора можеш ли да ми кажеш? :)
Ами аз си намерих отговора в друк форум ето какъв беше тои
Значи когато унищожаваш обект, подобект на други обекти, десструкторите за старшите обекти се включват автоматично. Тоест ако имаш обект Шаро, подобект на Куче, подобект на Млекопитаещи, то когато унищожиш Шаро ще се включи деструктора за Куче и после за Млекопитаещи.
Constructors and Destructors
Dog objects are Mammal objects. This is the essence of the is-a relationship. When Fido is created, his base constructor is called first, creating a Mammal. Then the Dog constructor is called, completing the construction of the Dog object. Because we gave Fido no parameters, the default constructor was called in each case. Fido doesn't exist until he is completely constructed, which means that both his Mammal part and his Dog part must be constructed. Thus, both constructors must be called.
When Fido is destroyed, first the Dog destructor will be called and then the destructor for the Mammal part of Fido. Each destructor is given an opportunity to clean up after its own part of Fido. Remember to clean up after your Dog! Listing 12.3 demonstrates this.
Listing 12.3. Constructors and destructors called.
1: //Listing 12.3 Constructors and destructors called.
2:
3: #include <iostream.h>
4: enum BREED { YORKIE, CAIRN, DANDIE, SHETLAND, DOBERMAN, LAB };
5:
6: class Mammal
7: {
8: public:
9: // constructors
10: Mammal();
11: ~Mammal();
12:
13: //accessors
14: int GetAge() const { return itsAge; }
15: void SetAge(int age) { itsAge = age; }
16: int GetWeight() const { return itsWeight; }
17: void SetWeight(int weight) { itsWeight = weight; }
18:
19: //Other methods
20: void Speak() const { cout << "Mammal sound!\n"; }
21: void Sleep() const { cout << "shhh. I'm sleeping.\n"; }
22:
23:
24: protected:
25: int itsAge;
26: int itsWeight;
27: };
28:
29: class Dog : public Mammal
30: {
31: public:
32:
33: // Constructors
34: Dog();
35: ~Dog();
36:
37: // Accessors
38: BREED GetBreed() const { return itsBreed; }
39: void SetBreed(BREED breed) { itsBreed = breed; }
40:
41: // Other methods
42: void WagTail() { cout << "Tail wagging...\n"; }
43: void BegForFood() { cout << "Begging for food...\n"; }
44:
45: private:
46: BREED itsBreed;
47: };
48:
49: Mammal::Mammal():
50: itsAge(1),
51: itsWeight(5)
52: {
53: cout << "Mammal constructor...\n";
54: }
55:
56: Mammal::~Mammal()
57: {
58: cout << "Mammal destructor...\n";
59: }
60:
61: Dog::Dog():
62: itsBreed(YORKIE)
63: {
64: cout << "Dog constructor...\n";
65: }
66:
67: Dog::~Dog()
68: {
69: cout << "Dog destructor...\n";
70: }
71: int main()
72: {
73: Dog fido;
74: fido.Speak();
75: fido.WagTail();
76: cout << "Fido is " << fido.GetAge() << " years old\n";
77: return 0;
78: }
Output: Mammal constructor...
Dog constructor...
Mammal sound!
Tail wagging...
Fido is 1 years old
Dog destructor...
Mammal destructor...
Analysis: Listing 12.3 is just like Listing 12.2, except that the constructors and destructors now print to the screen when called. Mammal's constructor is called, then Dog's. At that point the Dog fully exists, and its methods can be called. When fido goes out of scope, Dog's destructor is called, followed by a call to Mammal's destructor.
Passing Arguments to Base Constructors
It is possible that you'll want to overload the constructor of Mammal to take a specific age, and that you'll want to overload the Dog constructor to take a breed. How do you get the age and weight parameters passed up to the right constructor in Mammal? What if Dogs want to initialize weight but Mammals don't?
Base class initialization can be performed during class initialization by writing the base class name, followed by the parameters expected by the base class. Listing 12.4 demonstrates this.
Listing 12.4. Overloading constructors in derived classes.
1: //Listing 12.4 Overloading constructors in derived classes
2:
3: #include <iostream.h>
4: enum BREED { YORKIE, CAIRN, DANDIE, SHETLAND, DOBERMAN, LAB };
5:
6: class Mammal
7: {
8: public:
9: // constructors
10: Mammal();
11: Mammal(int age);
12: ~Mammal();
13:
14: //accessors
15: int GetAge() const { return itsAge; }
16: void SetAge(int age) { itsAge = age; }
17: int GetWeight() const { return itsWeight; }
18: void SetWeight(int weight) { itsWeight = weight; }
19:
20: //Other methods
21: void Speak() const { cout << "Mammal sound!\n"; }
22: void Sleep() const { cout << "shhh. I'm sleeping.\n"; }
23:
24:
25: protected:
26: int itsAge;
27: int itsWeight;
28: };
29:
30: class Dog : public Mammal
31: {
32: public:
33:
34: // Constructors
35: Dog();
36: Dog(int age);
37: Dog(int age, int weight);
38: Dog(int age, BREED breed);
39: Dog(int age, int weight, BREED breed);
40: ~Dog();
41:
42: // Accessors
43: BREED GetBreed() const { return itsBreed; }
44: void SetBreed(BREED breed) { itsBreed = breed; }
45:
46: // Other methods
47: void WagTail() { cout << "Tail wagging...\n"; }
48: void BegForFood() { cout << "Begging for food...\n"; }
49:
50: private:
51: BREED itsBreed;
52: };
53:
54: Mammal::Mammal():
55: itsAge(1),
56: itsWeight(5)
57: {
58: cout << "Mammal constructor...\n";
59: }
60:
61: Mammal::Mammal(int age):
62: itsAge(age),
63: itsWeight(5)
64: {
65: cout << "Mammal(int) constructor...\n";
66: }
67:
68: Mammal::~Mammal()
69: {
70: cout << "Mammal destructor...\n";
71: }
72:
73: Dog::Dog():
74: Mammal(),
75: itsBreed(YORKIE)
76: {
77: cout << "Dog constructor...\n";
78: }
79:
80: Dog::Dog(int age):
81: Mammal(age),
82: itsBreed(YORKIE)
83: {
84: cout << "Dog(int) constructor...\n";
85: }
86:
87: Dog::Dog(int age, int weight):
88: Mammal(age),
89: itsBreed(YORKIE)
90: {
91: itsWeight = weight;
92: cout << "Dog(int, int) constructor...\n";
93: }
94:
95: Dog::Dog(int age, int weight, BREED breed):
96: Mammal(age),
97: itsBreed(breed)
98: {
99: itsWeight = weight;
100: cout << "Dog(int, int, BREED) constructor...\n";
101: }
102:
103: Dog::Dog(int age, BREED breed):
104: Mammal(age),
105: itsBreed(breed)
106: {
107: cout << "Dog(int, BREED) constructor...\n";
108: }
109:
110: Dog::~Dog()
111: {
112: cout << "Dog destructor...\n";
113: }
114: int main()
115: {
116: Dog fido;
117: Dog rover(5);
118: Dog buster(6,8);
119: Dog yorkie (3,YORKIE);
120: Dog dobbie (4,20,DOBERMAN);
121: fido.Speak();
122: rover.WagTail();
123: cout << "Yorkie is " << yorkie.GetAge() << " years old\n";
124: cout << "Dobbie weighs ";
125: cout << dobbie.GetWeight() << " pounds\n";
126: return 0;
127: }
--------------------------------------------------------------------------------
NOTE: The output has been numbered here so that each line can be referred to in the analysis.
--------------------------------------------------------------------------------
Output: 1: Mammal constructor...
2: Dog constructor...
3: Mammal(int) constructor...
4: Dog(int) constructor...
5: Mammal(int) constructor...
6: Dog(int, int) constructor...
7: Mammal(int) constructor...
8: Dog(int, BREED) constructor....
9: Mammal(int) constructor...
10: Dog(int, int, BREED) constructor...
11: Mammal sound!
12: Tail wagging...
13: Yorkie is 3 years old.
14: Dobbie weighs 20 pounds.
15: Dog destructor. . .
16: Mammal destructor...
17: Dog destructor...
18: Mammal destructor...
19: Dog destructor...
20: Mammal destructor...
21: Dog destructor...
22: Mammal destructor...
23: Dog destructor...
24: Mammal destructor...
Analysis: In Listing 12.4, Mammal's constructor has been overloaded on line 11 to take an integer, the Mammal's age. The implementation on lines 61-66 initializes itsAge with the value passed into the constructor and initializes itsWeight with the value 5.
Dog has overloaded five constructors, on lines 35-39. The first is the default constructor. The second takes the age, which is the same parameter that the Mammal constructor takes. The third constructor takes both the age and the weight, the fourth takes the age and breed, and the fifth takes the age, weight, and breed.
Note that on line 74 Dog's default constructor calls Mammal's default constructor. Although it is not strictly necessary to do this, it serves as documentation that you intended to call the base constructor, which takes no parameters. The base constructor would be called in any case, but actually doing so makes your intentions explicit.
The implementation for the Dog constructor, which takes an integer, is on lines 80-85. In its initialization phase (lines 81-82), Dog initializes its base class, passing in the parameter, and then it initializes its breed.
Another Dog constructor is on lines 87-93. This one takes two parameters. Once again it initializes its base class by calling the appropriate constructor, but this time it also assigns weight to its base class's variable itsWeight. Note that you cannot assign to the base class variable in the initialization phase. Because Mammal does not have a constructor that takes this parameter, you must do this within the body of the Dog's constructor.
Walk through the remaining constructors to make sure you are comfortable with how they work. Note what is initialized and what must wait for the body of the constructor.
The output has been numbered so that each line can be referred to in this analysis. The first two lines of output represent the instantiation of Fido, using the default constructor.
In the output, lines 3 and 4 represent the creation of rover. Lines 5 and 6 represent buster. Note that the Mammal constructor that was called is the constructor that takes one integer, but the Dog constructor is the constructor that takes two integers.
After all the objects are created, they are used and then go out of scope. As each object is destroyed, first the Dog destructor and then the Mammal destructor is called, five of each in total.