Output of C++ Program | Set 17

　　Predict the output of following C++ programs.

Question 1

 1 #include <iostream>
 2 using namespace std;
 3
 4 class A
 5 {
 6 public:
 7     A& operator=(const A&a)
 8     {
 9         cout << "A's assignment operator called" << endl;
10         return *this;
11     }
12 };
13
14 class B
15 {
16     A a[2];
17 };
18
19 int main()
20 {
21     B b1, b2;
22     b1 = b2;
23     return 0;
24 }

　　Output:

　　A's assignment operator called
　　A's assignment operator called
　　The class B doesn’t have user defined assignment operator. If we don’t write our own assignment operator, compiler creates a default assignment operator. The default assignment operator one by one copies all members of right side object to left side object. The class B has 2 members of class A. They both are copied in statement “b1 = b2″, that is why there are two assignment operator calls.

Question 2

 1 #include<stdlib.h>
 2 #include<iostream>
 3
 4 using namespace std;
 5
 6 class Test
 7 {
 8 public:
 9     void* operator new(size_t size);
10     void operator delete(void*);
11     Test()
12     {
13         cout<<"\n Constructor called";
14     }
15     ~Test()
16     {
17         cout<<"\n Destructor called";
18     }
19 };
20
21 void* Test::operator new(size_t size)
22 {
23     cout<<"\n new called";
24     void *storage = malloc(size);
25     return storage;
26 }
27
28 void Test::operator delete(void *p )
29 {
30     cout<<"\n delete called";
31     free(p);
32 }
33
34 int main()
35 {
36     Test *m = new Test();
37     delete m;
38     return 0;
39 }

　　Output：

　　new called
 　 Constructor called
     Destructor called
    delete called

　　
　　Let us see what happens when below statement is executed.

  Test *x = new Test; 

　　When we use new keyword to dynamically allocate memory, two things happen: memory allocation and constructor call. The memory allocation happens with the help of operator new. In the above program, there is a user defined operator new, so first user defined operator new is called, then constructor is called.
The process of destruction is opposite. First, destructor is called, then memory is deallocated.

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　　2013-11-27　　16:44:03