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What does it mean to assign zero to a function?

Posted on 2013-06-10
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Last Modified: 2013-06-10
class Socket
{
  public:
   ...
   ..
   virtual ~Socket() {};

    virtual signed int close    () = 0;



What does it mean to assign 0 to close()?
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Question by:naseeam
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by:jkr
jkr earned 250 total points
ID: 39235984
It means that 'close()' is declared as a so called 'pure virtual' function, i.e. is expected to be overridden by a derived class. You cannot instantiate a class that has any pure virtual functions, they serve as a "interface definition". See also http://www.exforsys.com/tutorials/c-plus-plus/c-pure-virtual-function-and-base-class.html
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Author Comment

by:naseeam
ID: 39235999
class Socket
{
  public:
   ...
   ..
   virtual ~Socket() {};

    virtual signed int close    () = 0;


   /* Is this also pure virtual fucntion?  Will this be overridden by derived class
      as well. */
   virtual signed int openWait () {return SocketErrorValue_None;}
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LVL 86

Accepted Solution

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jkr earned 250 total points
ID: 39236023
No, this funtion is virtual, not "pure virtual". That means you canoverwrite it, but - as opposed to "pure virtual" - you don't have to.
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Author Closing Comment

by:naseeam
ID: 39236196
Excellent concise answers!  Short but complete.

Great link on C++ training.  Thank you so much!
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