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Full Discussion: C++ overriding Vs hiding
Top Forums Programming C++ overriding Vs hiding Post 302342671 by Corona688 on Monday 10th of August 2009 11:42:23 AM
Old 08-10-2009
Consider this code:
Code:
#include <stdio.h>

class B
{
public:
        void fns(void){ fprintf(stderr, "B::fns\n"); }
};

class D:public B
{
public:
        void fns(void) {fprintf(stderr, "D::fns\n"); }
};

void call_fns(B &obj)   {       obj.fns();      }

int main(void)
{
        D d;
        call_fns(d);
}

It will print "B::fns" because when the object is cast into its parent "B", the compiler no longer knows it should be calling D::fns. Without virtual functions, the compiler calls member functions based on the class type alone; casting it into its parent class loses all the functions you overrode.

But when we do this:
Code:
#include <stdio.h>

class B
{
public:
        virtual void fns(void){ fprintf(stderr, "B::fns\n"); }
};

class D:public B
{
public:
        virtual void fns(void) {fprintf(stderr, "D::fns\n"); }
};

void call_fns(B &obj)   {       obj.fns();      }

int main(void)
{
        D d;
        call_fns(d);
}

This time it will print D::fns. Virtual tells the compiler to remember if a function has been overloaded, even if it is cast into a parent class. It does so with a hidden variable, so keep in mind that using virtuals has a small performance cost, and increases the size of the class.
 

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LEARN ABOUT PHP

recursivedirectoryiterator

RECURSIVEDIRECTORYITERATOR(3)						 1					     RECURSIVEDIRECTORYITERATOR(3)

The RecursiveDirectoryIterator class

INTRODUCTION

	The RecursiveDirectoryIterator provides an interface for iterating recursively over filesystem directories.

CLASS SYNOPSIS

       RecursiveDirectoryIterator

       RecursiveDirectoryIteratorextends
       FilesystemIteratorSeekableIteratorRecursiveIterator

       Methods

       o public  RecursiveDirectoryIterator::__construct  (string   $path,  [int   $flags = FilesystemIterator::KEY_AS_PATHNAME | FilesystemItera-
	 tor::CURRENT_AS_FILEINFO])

       o public mixed RecursiveDirectoryIterator::getChildren (void  )

       o public string RecursiveDirectoryIterator::getSubPath (void  )

       o public string RecursiveDirectoryIterator::getSubPathname (void  )

       o public bool RecursiveDirectoryIterator::hasChildren ([bool  $allow_links = false])

       o public string RecursiveDirectoryIterator::key (void  )

       o public void RecursiveDirectoryIterator::next (void  )

       o public void RecursiveDirectoryIterator::rewind (void  )

       Inherits

       o public FilesystemIterator::__construct (string  $path, [int   $flags  =  FilesystemIterator::KEY_AS_PATHNAME  |  FilesystemIterator::CUR-
	 RENT_AS_FILEINFO | FilesystemIterator::SKIP_DOTS])

       o public mixed FilesystemIterator::current (void  )

       o public int FilesystemIterator::getFlags (void	)

       o public string FilesystemIterator::key (void  )

       o public void FilesystemIterator::next (void  )

       o public void FilesystemIterator::rewind (void  )

       o public void FilesystemIterator::setFlags ([int  $flags])

CHANGELOG

       +--------------+---------------------------------------------------+
       |   Version    | 						  |
       |	      | 						  |
       |	      | 		   Description			  |
       |	      | 						  |
       +--------------+---------------------------------------------------+
       |    5.3.0     | 						  |
       |	      | 						  |
       |	      |  The  FilesystemIterator  was  introduced  as the |
       |	      | parent class.  Previously,  the  parent  was  the |
       |	      | DirectoryIterator.				  |
       |	      | 						  |
       |    5.3.0     | 						  |
       |	      | 						  |
       |	      | 	   Implements SeekableIterator. 	  |
       |	      | 						  |
       |5.2.11, 5.3.1 | 						  |
       |	      | 						  |
       |	      | Added RecursiveDirectoryIterator::FOLLOW_SYMLINKS |
       |	      | 						  |
       +--------------+---------------------------------------------------+
PHP Documentation Group 											     RECURSIVEDIRECTORYITERATOR(3)
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