Implicit member functions of a Class in C++

Question

The implicit member functions of a Class in C++ are: As per wiki: http://en.wikipedia.org/wiki/Special_member_functions

Default constructor (if no other constructor is explicitly declared)

Copy constructor if no move constructor or move assignment operator is explicitly declared.If a destructor is declared generation of a copy constructor is deprecated.

Move constructor if no copy constructor, move assignment operator or destructor is explicitly declared.

Copy assignment operator if no move constructor or move assignment operator is explicitly declared.If a destructor is declared generation of a copy assignment operator is deprecated.

Move assignment operator if no copy constructor, copy assignment operator or destructor is explicitly declared.

Destructor

As per link below:

http://archives.cs.iastate.edu/documents/disk0/00/00/02/43/00000243-02/lcpp_136.html

A default constructor (i.e., one with no parameters, (section 12.1 [Ellis-Stroustrup90]), if no constructor (with any number of arguments) for the class has been declared.

A copy constructor (section 12.1 [Ellis-Stroustrup90]), if no copy constructor has been declared.

A destructor (section 12.4 [Ellis-Stroustrup90]), if no destructor has been declared.

An assignment operator (sections 5.17 and 12.8 of [Ellis-Stroustrup90]), if no assignment operator has been declared.

As per link below:

http://www.picksourcecode.com/ps/ct/16515.php

default constructor

copy constructor

assignment operator

default destructor

address operator

Can some one give code examples for : Move constructor,Copy assignment operator,Move assignment operator,An assignment operator,address operator where they are being used as implicit member functions and not defined explicitly.

Thanks

jogojapan · Accepted Answer · 2013-02-14 05:26:21Z

5

#include <iostream>

/* Empty struct. No function explicitly defined. */    
struct Elem
{ };

/* Factory method that returns an rvalue of type Elem. */
Elem make_elem()
{ return Elem(); }


int main() {

  /* Use implicit move constructor (the move may be elided
     by the compiler, but the compiler won't compile this if
     you explicitly delete the move constructor): */
  Elem e1 = make_elem();

  /* Use copy assignment: */
  Elem e2;
  e2 = e1;

  /* Use move assignment: */    
  e2 = make_elem();

  /* Use address operator: */    
  std::cout << "e2 is located at " << &e2 << std::endl;

  return 0;
}

The example above uses an empty class. You can fill it with data members that have real move semantics (i.e. members where moving is really different from copying), e.g. a std::vector, and you'll get move semantics automatically without defining move constructors or move assignment operators specifically for your class.

edited Feb 14, 2013 at 5:26

answered Feb 14, 2013 at 5:17

jogojapan

70.5k11 gold badges110 silver badges136 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

Gaurav K Over a year ago

/* Use copy assignment: */ Elem e2; e2 = e1; This explaind copy constructor and assignment operator as well , right?

jogojapan Over a year ago

e2 = e1 is a copy assignment, it does not involve the copy constructor (because e2 is not constructed -- it exists already). If you want the copy constructor, you'd need to say Elem e2 = e1; all on one line.

Gaurav K Over a year ago

How would you differentiate assignment operator and copy assignment then?

jogojapan Over a year ago

e2 = e1; is copy assignment, e2 = make_elem(); is move assignment. Both are assignment operators, and both are implicitly defined. (But "assignment operator" is a term with an even broader meaning, e.g. e2 = 3; or e2 += 12.3; use assignment operators, too, but those are not defined implicitly, you'd have to define them yourself (as operator=(int) and operator+=(float), respectively).

Collectives™ on Stack Overflow

Implicit member functions of a Class in C++

1 Answer 1

4 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

4 Comments

Your Answer

Sign up or log in

Post as a guest

Related