Why Copy Constructor is called, not Assignment operator here : "Cents cNancy = cMark;"

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Cents cNancy = cMark; //cMark is existing object

Here Copy Constructor is called, not Assignment operator?

Can any one tell why?

Thanks

Posted 18-May-13 7:32am

iDebD

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PIEBALDconsult 18-May-13 13:48pm

Not without more information we can't.

3 solutions

Solution 3

There is a difference between assignment and initialization.

Initialization looks like this - int i = 10;
Assignment looks like this - int i; i = 10;

So the rule is simple - Assignment operator is used for assignment.

Posted 19-May-13 16:09pm

«_Superman_»

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Santhosh G_ · Accepted Answer · 2013-05-18T07:44:00

Solution 1

Here assuming that Cents as a class, cNancy, cMark instances of Cents class.

Cents cNancy; // here default constructor will be called.
cNancy = cMark; // here assignment operator will be invoked.
Cents cNancy = cMark;// Here new object cNancy is created from cMark by
calling copy constructor.

Posted 18-May-13 7:44am

Santhosh G_

Updated 18-May-13 8:12am

v2

Comments

PIEBALDconsult 18-May-13 13:48pm

Any evidence to back your claim?

Steve44 18-May-13 16:35pm

This is an optimization designed into the C++ language, whenever an object exists before, the assignment operator is invoked, whenever an object is to be constructed, the CopyConstructor is invoked. This avoids the inefficiency of a DefaultConstruction followed by an assignment vs. a CopyConstructor which should be semantically equivalent anyway.
Take a look here:
http://www.learncpp.com/cpp-tutorial/911-the-copy-constructor-and-overloading-the-assignment-operator/

Santhosh G_ 18-May-13 14:02pm

Here i expected Cents is a class, cNancy is an instance of a Cents class.
When creating an instance of Cents cNancy with an existing instance cMark copy constructor will be called. Could you please explain the problem. Do I have to explain anything else.

CPallini · Accepted Answer · 2013-05-18T10:38:00

Solution 2

Because that is a C++ rule.

C++

Cents cNancy = cMark;

is the same as

C++

Cents cNancy(cMark);

That is variable initialization: see, for instance, Herb Sutter's GotW #1 - Variable initialization[^].

Posted 18-May-13 10:38am

CPallini