Initializing data-member references using initialization lists in C++

Question

Fellow Stackers,

Consider the following two simple classes in the header file:

Class CC
{
 public:
 CC(int& value);
 C& operator=(const C& other);
 {
   cout<<" From copy constructor ";
 }

 int m_cc;
};

Class AA
{
 public:
 AA( CC& refCC);

 CC m_cInstance;
}

The following is in the .cpp file.

CC:CC(int& value): m_cc(value)
{
   cout<<" Constructor of CC" <<endl;
   m_cc++;
}

AA:AA(CC& refCC): m_cInstance(refCC)
{
   cout<<" The value of m_cc in refCC is: "<< refCC.m_cc; 
   cout<<" The address of m_cc in refCC is: "<< &refCC.m_cc;
   cout<<" The address of refCC is: "<< &refCC;

   cout<<" The value of m_cc in m_cInstance is: <<m_cInstance.m_cc;
   cout<<" The address of m_cc in m_cInstance is: <<&m_cInstance.m_cc;
   cout<<" The address of m_cInstance is: <<&m_cInstance;
}

I use the above two declared simple classes in the follwing way in my main.cpp file:

int cvalue = 1000; CC refCC(cvalue);

AA aaObj(refCC);

Here is the output of the program:

 Constructor of CC
 The value of m_cc in refCC is: 1001
 The address of m_cc in refCC is: 0x12ff20
 The address of refCC is: 0x12ff20

 The value of m_cc in m_cInstance is: 1001
 The address of m_cc in m_cInstance is: 0x12ff14
 The address of m_cInstance is: 0x12ff14

Here are few observations:

Notice that address of m_cInstance in the instance AA is different from the address of refCC.
Though the instance of CC is passed by reference(refCC) in the constructor of AA, the member variable "m_cInstance" is seperate instance by itself.
Constructor of the instance to CC is called once when "refCC" is created even though two distinct instances of CC are present in the program carrying the same state.
The overridden assignment operator is never called.

My question is simple:

How is the "m_cInstance" created in the constructor of AA without a call to constructor of CC or the assignment operator defined in CC ??

And if CC contains a handle to a file on disk as a member variable ? What is its behavior in "m_cInstance"??

Thanks,

De Costo.

1. You should cut and paste your real code. Your constructors have syntax errors. 2. `operator=` is not a copy constructor, it's an assignment operator. And you are correct, your code never uses it. It uses copy construction, but you haven't defined a copy constructor. — C. K. Young, Aug 09 '11 at 19:26
`CC:CC(int& value)::m_cc(value)` should be like `CC::CC(int& value):m_cc(value)` did you type the code in here? — A. K., Aug 09 '11 at 19:27
The line "AA:AA(CC& refCC): m_cc(refCC)" would never compile since you have no member "m_cc" in class "AA". Hence you're not posting the code that you're asking about. It's pretty silly to ask about code X and post code Y. — Cheers and hth. - Alf, Aug 09 '11 at 19:27
still there is a missing `colon` in here CC:CC(int& value) and here AA:AA(CC& refCC) — A. K., Aug 09 '11 at 19:54

score 2 · Answer 1 · edited May 23 '17 at 12:04

2

m_cInstance is created using the (compiler provided in your case) copy constructor. As a sanity check, if you need to define the assignment operator, you probably need to define the copy constructor and the destructor as well (know as the rule of three here and on wikipedia)

edited May 23 '17 at 12:04

Community

1
1

answered Aug 09 '11 at 19:28

AProgrammer

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What other constructs or methods are created by default for a class ?? Is it part of the standard ?? – Vishnu Pedireddi Aug 09 '11 at 19:36
1

See http://stackoverflow.com/questions/4172722, they are given there. Yes, it is standard. – AProgrammer Aug 09 '11 at 19:43

score 0 · Answer 2 · answered Aug 09 '11 at 19:29

0

You're copy constructing to create m_cInstance so it doesn't appear that you log that. m_cInstance is updated once with a copy of refCC and won't change even if the refCC changes outside the instance.

answered Aug 09 '11 at 19:29

Mark B

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score 0 · Answer 3 · answered Aug 09 '11 at 19:52

there is a copy constructor that is provided to your class (by the compiler) and if i understand correctly you are probably confusing the operator=(const C& other) that you have defined with the copy constructor.

For a class CC the copy constructor will have have a declaration like this

CC(const CC& C);

Initializing data-member references using initialization lists in C++

3 Answers3