The proper way of function encapsulation.
From: Val (valmont_programming_at_hotmail.com)
Date: 07/27/04
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Date: Tue, 27 Jul 2004 04:53:42 +0200
Concerning the code below, wich serves as getting aquinted with the priority queue.
I'll ask my questions after the code:
#include <iostream>
#include <vector>
#include <queue>
#include <functional>
using namespace std;
class SomeClass
{
public:
int someProperty;
};
//Override original less for any class/struct that holds a "someProperty".
//Assumes operator<() is defined on T.
template<typename T>
class less : binary_function<T, T, bool>
{
public:
bool operator()(const T& a, const T& b) const
{
return a.someProperty < b.someProperty;
}
};
typedef priority_queue<SomeClass, vector<SomeClass>, less<SomeClass> > PQ;
//For basic function encapsulation demonstrational purpose only!
//Assumes the existence of SomeClass.
//Assumes SomeClass holds a public member "int somePropery".
class PQueue
{
public: //Main methods
void enterNumber();
void popPq();
void showHeap();
void Menu();
public: //Various
enum {Exit, Push, Pop, Top};
private: //Members
PQ MP;
SomeClass SC;
};
int main()
{
PQueue TestPQueue;
TestPQueue.Menu();
return 0;
}
void PQueue::Menu()
{
int input=1;
while (input != 0)
{
cout << "\nEnter a Selection:\n";
cout << "0) Exit\n";
cout << "1) Push a Number\n";
cout << "2) Pop the heap\n";
cout << "3) Show top of heap\n";
cin >> input;
switch(input)
{
case Exit: cout << "Exited.\n"; break;
case Push: enterNumber(); break;
case Pop: popPq(); break;
case Top: showHeap(); break;
default: cout << "ERROR, reason: Incorrect Entry\n";
}
}
}
void PQueue::enterNumber()
{
cout << "---> ";
cin >> SC.someProperty;
MP.push(SC);
}
void PQueue::popPq()
{
if(!MP.empty())
{
cout << "Popping top of heap (" <<
MP.top().someProperty << ")" << endl;
MP.pop();
}
else
cout<<"*Empty Heap*\n";
}
void PQueue::showHeap()
{
cout << "Top of the heap is: ";
if(!MP.empty())
cout<< MP.top().someProperty;
else
cout<<"*Empty Heap*";
cout<<"\n";
}
It's PQueue what bothers me.
What I wanted to achieve is to encapsulate "push", "pop" and "top" and actually also the "view" (showHeap).
So I made this PQueue class to experiment. But I don't like it. It doesn't feel good. I can't say "it isn't
right" because I am way too much unexperianced for such a remark.
But I don't like it at all.
I *could* have derrived PQueue from "priority_queue<SomeClass, vector<SomeClass>, less<SomeClass> >" (somehow)
to specialize the class but basically my question is:
How do I encapsulate these kind of standard methods? I don't understand Bjarne S. explanation about interface
classses or handle classes so I am lost.
I'll post some code of a linked list implementation with some basic encapsulation in a class. So you'll
understand how I got to this little task:
#include <iostream>
#include <string>
using namespace std;
struct Node
{
int Item;
Node *Next;
};
class LinkedList
{
public:
void AddItem(int itm);
void ShowItems();
//Dtors, Ctors etc.
public:
LinkedList() : m_nodeStart(0){ }
~LinkedList();
private:
Node* m_nodeStart;
};
void LinkedList::AddItem(int itm)
{
Node* p = m_nodeStart;
m_nodeStart = new Node;
m_nodeStart->Next = p;
m_nodeStart->Item = itm;
}
void LinkedList::ShowItems()
{
for(Node* p = m_nodeStart; p != 0; p = p->Next)
cout<<p->Item<<" ";
cout<<endl;
}
LinkedList::~LinkedList()
{
Node* p;
while(m_nodeStart != 0)
{
p = m_nodeStart;
m_nodeStart = m_nodeStart->Next;
delete p;
}
}
int main ()
{
LinkedList MyList;
MyList.AddItem(15);
MyList.AddItem(30);
MyList.AddItem(45);
MyList.ShowItems();
return 0;
}
See? No biggie here. But how do I this with the priority queue? Or did manage it well already?
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