Marc Ellis, on 02 August 2010 - 11:39 AM, said:

its a blank screen because there is no data to display. click menu and add data and you will see it on your screen

So how then do you add data into the menu?
Cos you can't click what you don't see right?

upper_bound does return an iterator to one past the element you are looking for. This is always supported also when the element found is the last element, it will just return an iterator one past the end of the container, which is valid in stl world.

What is not safe (read undefined) is dereferencing this iterator. So you might want to do a check like.

if (great != list.end())

before you do

cout<<"The next element in the set is "<<*great<<endl;

#include <iostream>
#include <set>
using namespace std;

int main(){
	int x;
	int a[12] ={2,4,6,5,8,9,10,3,7,1,15,12};
	std::set<int> list; 
	std::set<int>::iterator it, ti, great;
	for(int i = 0; i<12; i++){
		x = a[i];
		list.insert(x);
	}
	ti = list.begin(); //assign pointer to the first node of the set (first element)
	for(it = list.begin(); it!=list.end(); it++)
		cout<<*it<<endl;

	cout<<"\nSearch for a value in the above list"<<endl;
	cin>>x;
	if(list.count(x) !=0){   //search for existing value in list returns 1 if found and 0 otherwise
		it = list.find(x);   //find the value in the list and assign pointer to the value
		great =list.upper_bound(x);
		if((*it) &&(*great)){    
			
				cout<<"found value "<<*it<<endl;
				cout<<"the element is in "<<distance(ti,it)+1<<"th position"<<endl;
				cout<<"The next element in the set is "<<*great<<endl;
                                   /* try{
					great =list.upper_bound(x);
					cout<<"The next element in the set is "<<*great<<endl;
				       }
				   catch(int e){
					cout<<"Error! no element after the last element in the container"<<endl;
				    }*/
		}
		else
				cout<<"end of list no element after "<<*it<<endl;
	}
	else
			cout<<"value not in list"<<endl;

	return 0;
}

from my understanding of upper_bound(x) it returns a pointer to the next element greater than x
in my code it seems to be working fine.. but my problem is if the user tries accessing the last element
the program crashes since there is no other element to compare so it points to an invalid address.. how do i avoid this crash and output an error message instead of crashing.. i've tried using throw and catch method...

ketybrown, on 08 December 2011 - 03:48 AM, said:

Polymorphism means an object of a base type can behave as an object of a more derived type. In c++ world this means that the base type must have atleast one virtual method. This is not required to avoid slicing.

But slicing can only be avoided when assigning an object of a more derived type to something of a base type if that something is a pointer or a reference.


Also know that when you assign it to a pointer of a base type and that pointer is responsible for the lifetime of the object, then the base class needs at least a virtual destructor. For example:

A* a = new B();
delete a; //<-This causes a memory leak if A's destructor is not virtual

This is a very common cause of memory leaks and actually another form of slicing. delete a will call the destructor of class A if it is not virtual, which will clean up the A part but not the B part.

ketybrown, on 07 December 2011 - 08:47 AM, said:

Hmm, ok but beware to only do a static_cast<B*> on pointers that actually point to an object of type B. No

A c;
c = B();
static_cast<B*>->print();

This is wrong !!!

The compiler won't stop you from doing this, but behavior is undefined. If uncertain use dynamic_cast, it will return NULL when you're doing it wrong.