dcsimg
Login | Register   
LinkedIn
Google+
Twitter
RSS Feed
Download our iPhone app
TODAY'S HEADLINES  |   ARTICLE ARCHIVE  |   FORUMS  |   TIP BANK
Browse DevX
Sign up for e-mail newsletters from DevX

By submitting your information, you agree that devx.com may send you DevX offers via email, phone and text message, as well as email offers about other products and services that DevX believes may be of interest to you. DevX will process your information in accordance with the Quinstreet Privacy Policy.


Tip of the Day
Language: C++
Expertise: All
Feb 11, 2000

WEBINAR:

On-Demand

Building the Right Environment to Support AI, Machine Learning and Deep Learning


Declaring an Object With No Default Constructor as a Member of Another Class

Suppose you have a class called A, which doesn't have a default constructor, and you want to embed an instance of this class as a member of another class, B:

 
  class A
  {
  public:
    A (int n);   // no default constructor
  };

When you instantiate an ordinary object of class A, you pass an argument to its constructor like this:

 
  A a(3); // OK

However, you can't do that when declaring an instance of A as a member of another class:

 
  class B
  {
  public:
    B();
  private:
    A a(3); // error
  };

You should use a member-initialization list in the containing class's constructor to pass the embedded object's argument:

 
  class B
  {
  public:
    B() : a(3) {} // pass argument to embedded object
  private:
    A a; // no argument here
  };

Some classes have both a default constructor and a constructor that takes one or more arguments, (e.g., std::vector). With such classes, you should use a member-initialization list to invoke a constructor that takes arguments:

 
  class Document
  {
  private:
    vector <char> vc; // no argument here
  public:
    Document() : vc(80){} // similar to vector <char> vc (80)
  };
Danny Kalev
 
Comment and Contribute

 

 

 

 

 


(Maximum characters: 1200). You have 1200 characters left.

 

 

Sitemap
Thanks for your registration, follow us on our social networks to keep up-to-date