Get an error when trying to clear the heap space

Hey,
I am getting a runtime error when I run my removeSomeElement() function. Can someone have a look and tell me what I am doing wrong.
thanks a lot.

My Code is:

Code:

#include "Person.h"
class SetOfPersons{  //Unbounded Container 
public: 
     SetOfPersons(int n = 4) : index(0),size(n){ 
         buffer = new Person*[n]
      ;} 
 
    ~SetOfPersons(void) {delete [] buffer;} 
    
        void add(Person & item) { 
	 if(index == size) {  //grow the container 
                 cout << "growing\n"; 
                 Person ** temp = buffer; 
                 buffer = new Person*[size*2]; 
                 for(int i=0; i<size; i++) buffer[i] = temp[i]; 
                  size = size *2; 
                  delete [] *temp; 
                 } 
        buffer[index++] = &item; 
     } 
     
      int sizea(){ return index;}

     Person & removeSomeElement() { 
         index--; 
         if(index < size/2) {  //shrink the container 
	 return *buffer[++index];
	 cout << "shrinking\n"; 
                 Person ** temp = buffer; 
                 buffer = new Person*[size/2]; 
                for(int i=0; i<index; i++) buffer[i] = temp[i]; 
                   size = size/2; 
                   delete [] *temp; 
         } 
		 
      }        Person & someElement() {
           if(index>0){
              return *buffer[++index];
           }
          else{index=0;}
       }
	 

void printOn(ostream & ostr){ 
		 
	 } 


private: 
      Person ** buffer; 
      int size; 
      int index; 
}; 
ostream & operator<<(ostream & ostr, SetOfPersons & p) { 
     p.printOn(ostr); 
     return ostr; 
}

My main file is:

Code:

//file main.cpp 
#include <iostream.h>  
#include <string.h> 
#include "Date.h" 
#include "Person.h" 
#include "SetOfPersons.h" 

main() { 
int i;
//create some persons on the heap
Person *p1 = new Person("Lou", "lou@chat.ca", 20, 6, 1960); 
Person *p2 = new Person("Frank", "f123@chat.ca", 20, 3, 1967); 
Person *p3 = new Person("Ann", "ann@chat.ca", 20, 8, 1960); 
Person *p4 = new Person(); 
//Create some sets
SetOfPersons boys, girls; 

//Add some persons to the sets

boys.add(*p4); 

//test to see if the same object is retrieved from the set. 
if (p1 != &boys.removeSomeElement() ) 
  cout << "ERROR: the objects are different \n"; 
else 
  cout << "Good, the objects are the same \n"; 


boys.add( *p1); 
boys.add( *p2); 
girls.add( *p3); 

boys.add(*(new Person("John", "f123@chat.ca", 20, 3, 1967))); 
girls.add(*(new Person("Sue", "f123@chat.ca", 20, 3, 1967))); 
boys.add(*(new Person("Frank", "frank@chat.ca", 25, 4, 1958))); 
girls.add(*(new Person("Mary", "mary@chat.ca", 25, 4, 1955))); 
boys.add(*(new Person("John", "johnchat.ca", 12, 12, 1970))); 



//print all the boys using the removeSomeElement() method and delete them 
int numberOfBoys = boys.sizea(); 
cout << "number of boys = " << numberOfBoys << "\n"; 
for(i = 0; i<numberOfBoys; i++) { 
 Person & boy = boys.removeSomeElement(); 
  //cout << boy << "\n"; 
 // delete &boy;  
  } 
  

//print the girls using the << operator of the SetOfPersons class 

//cout << "number of girls = " << girls.sizaa() << "\n"; 
//cout << girls << "\n"; 

//print of the girls birthdays and using the someElement() method 
int numberOfGirls = girls.sizea(); 
//for(int i = 0; i<numberOfGirls; i++) 
  //cout << girl.someElement().getBirthDate() << "\n"; 
  

//delete all the girls from the heap 
numberOfGirls = girls.sizea(); 
for(i = 0; i<numberOfGirls; i++) { 
  Person & her = girls.removeSomeElement(); 
//  delete &her; 
  

} //end of main 

}

Your removeSomeElement() function doesn't always return a meaningful value.

how should I return the meaniful value. Sorry I am new to this and I cannot figuer out the problem. thanks

Since it doesn't return a value, make the return type void. This is the reason why it's good to explicitly state a return value.

Code:

 removeSomeElement();

This function prototype implicitly returns int since that's the compiler's default type, but we want to return nothing, so this doesn't work.

Code:

void removeSomeElement();

Now it returns nothing: void.

I am returning a value it is " return *buffer[++index];" it's in the second line and not on the end of the function.

thanks

so what does it return when if(index < size/2) turns out to be false?

what should I return if this is false.
if(index < size/2)

I tried return *this but that does not work.

Maybe you should return a pointer, NULL. If you return a reference it implies that you always have a value to return.

[edit]

I tried return *this but that does not work.

Of course that doesn't work. *this is a SetOfPersons, and the function returns a Person.
[/edit]

I tried that if index<size/2 then return an empty Person Object. That does not seem to work. My code looks like this:

Code:

 Person &removeSomeElement(){
		static Person InvalidPerson("","", 0, 0, 0);
		numberOfElements--; 
         if(numberOfElements < capacity/2) {  //shrink the container 
            cout << "shrinking\n"; 
            Person ** temp = elements; 
            elements = new Person*[capacity/2]; 
            for(int i=0; i<numberOfElements; i++) elements[i] = temp[i]; 
            capacity = capacity/2; 
            delete [] temp; 
         } 
		 else {
			return InvalidPerson;
		}
	}

That's why I think you should return a pointer instead. You can return NULL to indicate "no object".

You were right thanks alot that worked!!. I have one more question in my printOn Method how should I print the elements of the set . Does that mean that I loop through the array and print the elements out.

Code:

void printOn(ostream & ostr){ 
 for(int i=0; i<sizea(); i++)
 cout<<buffer[i];
}

When I do this I get an error on the //cout << boy << "\n"; line

Code:

int numberOfBoys = boys.sizea(); 
cout << "number of boys = " << numberOfBoys << "\n"; 
for(i = 0; i<numberOfBoys; i++) { 
 Person & boy = boys.removeSomeElement(); 
  //cout << boy << "\n"; 
 // delete &boy;  
  }

cout << object expects the object to have overloaded the << operator. If you use your own method instead of operator<<, you'll need to call it directly.

Code:

object.printOn();

Alternatively, you could make printOn return a string, that you print:

Code:

string printOn() {
    return "something";
}

cout << object.printOn();

You might want to choose a different name in that case.

Or you could just overload the << operator. That's pretty hard to do, though. Read up on it under "operator overloading".