Objects and Functions, Copy Constructors


Objects can be passed as regular variables (or references or pointers) to functions, but some care must taken be taken. When an object is passed as a parameter, an exact copy of the object is made without invoking the object s constructor. On the other hand, the object s destructor is called for that copy when it is no longer needed. Some objects ( especially ones where memory is allocated) will not work properly under these conditions.

In order to eliminate this problem, a class must implement a copy constructor , a special constructor that takes as an argument a const reference to that same type. For example:

 class Mobject 
{
public:
MObject(); // Regular constructor
Mobject( const Mobject &Original );// Note Original is not a required
name.
}

The copy constructor (instead of the default constructor) is called when an object is passed to a function, for autoinitialization, or when an object is returned from a function. It is not called during a normal assignment (you may write an overloaded operator to handle this). For example:

 Foo( SomeObject );   // Copy constructor called to make a 
copy of SomeObject
MObject A = B; // Copy ctor called for auto-initialization
B is an
MObject )
A = B; // Copy constructor is NOT called.



OOP Demystified
OOP Demystified
ISBN: 0072253630
EAN: 2147483647
Year: 2006
Pages: 130

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