DaniWeb Forum Index > Software Development > C++

C++ RSS

Type comparable

Please support our C++ advertiser: Intel Parallel Studio Home

•

Join Date: Feb 2008

Posts: 9

Reputation: jrkeller27 is an unknown quantity at this point

Solved Threads: 0

jrkeller27 jrkeller27 is offline

Offline

Newbie Poster

Type comparable

Feb 26th, 2008

In C++ is there a way to define a class to be "comparable"? What Im trying to do is write a class that holds a string and a vector of numbers. If an object of this type is compared to another object I want the string that each object contains to be the "thing" thats compared. The header of my class so far is:

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
#ifndef index_h
#define index_h
#include <String>
using namespace std;
class  index{
 
 public:
  index(string word);
 void putpage(int number);
 bool haspage(int number);
 
 
};
#endif
#ifndef index_h
#define index_h
#include <String>
using namespace std;
class  index{

 public:
  index(string word);
 void putpage(int number);
 bool haspage(int number);


};
#endif

Any input or help is appreciated, I'm new to c++

•

Join Date: Aug 2005

Posts: 15,502

Reputation: Ancient Dragon has a reputation beyond repute

Solved Threads: 1479

Ancient Dragon Ancient Dragon is offline

Offline

Still Learning

Re: Type comparable

Feb 26th, 2008

write an == operator

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
class  index{
 
 public:
  index(string word);
 void putpage(int number);
 bool haspage(int number);
 bool operator==(index& idx); // compare the two class objects
 
};
class  index{

 public:
  index(string word);
 void putpage(int number);
 bool haspage(int number);
 bool operator==(index& idx); // compare the two class objects

};

Last edited by Ancient Dragon; Feb 26th, 2008 at 6:56 pm.

Don't PM me with questions -- you might get a nasty PM in response. If you have a question then post it in one of the forums.

•

Join Date: Jun 2005

Posts: 2,052

Reputation: Rashakil Fol is just really nice

Solved Threads: 139

Rashakil Fol Rashakil Fol is offline

Offline

Super Senior Demiposter

Re: Type comparable

Feb 26th, 2008

You can also write operator< , operator<= , etc.

•

Join Date: Feb 2008

Posts: 9

Reputation: jrkeller27 is an unknown quantity at this point

Solved Threads: 0

jrkeller27 jrkeller27 is offline

Offline

Newbie Poster

Re: Type comparable

Feb 27th, 2008

Okay I have overloaded those operators and implemented it in my source file. Now my next question is what do I have to do to make this class able to be put into a Binary Search Tree. The BST I'm using does comparisons solely using the operator< so I think I have that set.

What type of syntax do I need to set my class to be of type comparable. Here is what my header file looks like after messing around and trying using template<type Comparable>. Note that I changed the class name to simply "structure"

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
#ifndef structure_h
#define structure_h
#include <vector>
#include <String>
#include "BinarySearchTree.h"
using namespace std;
template<class Comparable>
class BinarySearchTree;
 
 template<class Comparable> 
class structure{
 
public:
  string _word;
  vector<int> _indices;
  structure();
  structure(string word);
  structure(string word, int number);
 void putpage(int number);
 bool haspage(int number);
 bool operator< (const structure & rhs); // compare the two class objects
 
friend class BinarySearchTree<Comparable>;
};
 
#endif
#ifndef structure_h
#define structure_h
#include <vector>
#include <String>
#include "BinarySearchTree.h"
using namespace std;
template<class Comparable>
class BinarySearchTree;

 template<class Comparable> 
class structure{

public:
  string _word;
  vector<int> _indices;
  structure();
  structure(string word);
  structure(string word, int number);
 void putpage(int number);
 bool haspage(int number);
 bool operator< (const structure & rhs); // compare the two class objects

friend class BinarySearchTree<Comparable>;
};

#endif

Again, any input is greatly appreciated.

•

Join Date: Dec 2006

Posts: 1,089

Reputation: vijayan121 is a name known to all

Solved Threads: 164

vijayan121 vijayan121 is offline

Offline

Veteran Poster

Re: Type comparable

Feb 27th, 2008

> What type of syntax do I need to set my class to be of type comparable?

nothing at all; just declare and implement the comparison operator(s). in

Help with Code Tags

C++ Syntax (Toggle Plain Text)

template<class Comparable>
class BinarySearchTree;

Comparable is just a place holder; the above is equivalent to

Help with Code Tags

C++ Syntax (Toggle Plain Text)

template< class T >
class BinarySearchTree;

and your structure could be

Help with Code Tags

(Toggle Plain Text)

class structure
{
public:
  string _word;
  vector<int> _indices;
  structure();
  structure(string word);
  structure(string word, int number);
  void putpage(int number);
  bool haspage(int number);
  bool operator< (const structure & rhs) const ; // this should be a selector

  friend class BinarySearchTree<structure>;
};

this is how you could instantiate a BinarySearchTree of structures.

Help with Code Tags

C++ Syntax (Toggle Plain Text)

BinarySearchTree<structure> the_search_tree ;

and this would declare a function taking a binary search tree of structures as an argument

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
 void function( BinarySearchTree<structure>& tree ) ;
 void function( BinarySearchTree<structure>& tree ) ;

Last edited by vijayan121; Feb 27th, 2008 at 3:22 pm.

•

Join Date: Feb 2008

Posts: 9

Reputation: jrkeller27 is an unknown quantity at this point

Solved Threads: 0

jrkeller27 jrkeller27 is offline

Offline

Newbie Poster

Re: Type comparable

Feb 27th, 2008

Awesome thanks! Now I'm writing the implementation to the header file and I think the issues I'm getting are revolving around pointer issues, but I'm not sure. The pertinent code is:

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
 
structure::structure(){
    string _word;
    vector<int> *_indices();
}
//template <class Comparable>
structure::structure(string word){
   string _word;
   vector<int> *_indices();
 
 
}
 
//template <class Comparable>
structure::structure(string word, int number){
    string _word;
    vector<int> *_indices();
 
}
 
//template <class Comparable>
void structure::putpage(int number){
    *_indices->push_back(number);
}
 
//template <class Comparable>
bool structure::haspage(int number){
    vector<int>::iterator *iter;
    *iter=(_indices).begin();
    /*  for(*iter=*_indices->begin(); *iter!=*_indices->end();++*iter){
	if(*iter == number){
	    return true;
	}
	}*/
    return false;
structure::structure(){
    string _word;
    vector<int> *_indices();
}
//template <class Comparable>
structure::structure(string word){
   string _word;
   vector<int> *_indices();
    

}

//template <class Comparable>
structure::structure(string word, int number){
    string _word;
    vector<int> *_indices();
    
}

//template <class Comparable>
void structure::putpage(int number){
    *_indices->push_back(number);
}

//template <class Comparable>
bool structure::haspage(int number){
    vector<int>::iterator *iter;
    *iter=(_indices).begin();
    /*  for(*iter=*_indices->begin(); *iter!=*_indices->end();++*iter){
	if(*iter == number){
	    return true;
	}
	}*/
    return false;

What I'm trying to do with haspage(int number) is return a bool to see if the number is in the _indices vector. I'm also getting problems with putpage(int number) regarding void values not being ignored. Any help with syntax/pointer problems would be (again) appreciated.

•

Join Date: Dec 2006

Posts: 1,089

Reputation: vijayan121 is a name known to all

Solved Threads: 164

vijayan121 vijayan121 is offline

Offline

Veteran Poster

Re: Type comparable

Feb 27th, 2008

> I think the issues I'm getting are revolving around pointer issues ...
there are several issues. let us take them one by one.

Help with Code Tags

(Toggle Plain Text)

class structure
{

    public:
      string _word;
      vector<int> _indices;
      // ...
      structure() ; 

      // passing a string using const reference is more efficient;
      // we avoid the need to make a copy of a string
      structure( const string& word ) ;
      /// ...
      void putpage( int number ) ;
      bool haspage( int number ) ;
      // ....
};

these lines in the constructor(s) do nothing useful.

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
{
  // creates a string which is destroyed on return
  string _word;
 
  // this merely declares a function named _indices
  vector<int> *_indices();
}
{
  // creates a string which is destroyed on return
  string _word;
 
  // this merely declares a function named _indices
  vector<int> *_indices();
}

both the string and the vector have default constructors which would initialize them correctly. so the default constructor needs to be just

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
structure::structure() 
{ /* default initialization for _word, _indices */ }
structure::structure() 
{ /* default initialization for _word, _indices */ }

in a constructor, we could also initialize a member in a non-default way. eg.

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
structure::structure( const string& word ) : _word( word ) 
{ 
  // member _word initialized with word	 
  // default initialization for _indices 
}
structure::structure( const string& word ) : _word( word ) 
{ 
  // member _word initialized with word	 
  // default initialization for _indices 
}

to add a number to the vector indices

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
void structure::putpage( int number ) 
{ _indices.push_back( number ) ; }
void structure::putpage( int number ) 
{ _indices.push_back( number ) ; }

to check weather a number is present in the vector indices, you could iterate through the vector looking for the number, or (easier) use the algorithm std::find

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
#include <algorithm>
bool structure::haspage( int number ) 
{ 
  return std::find( _indices.begin(), _indices.end(), number )
                != _indices.end() ;
}
#include <algorithm>
bool structure::haspage( int number ) 
{ 
  return std::find( _indices.begin(), _indices.end(), number )
                != _indices.end() ;
}