Yet another Segmentation Fault (Debugging 2)

Points : 20

Remove error(s)/segmentation fault(s)/warning(s) from the given CPP code by

1. Deleting exactly three characters (7 marks)
2. Adding exactly one keyword (5 marks)

In addition to above changes by further deleting exactly three characters (8 marks), change c1 contents such that

	c1.id[0]=c1.id[1]=c1.id[2]=0;
	c1.id[3]=200;

For all the changes you do, you need to provide proper explanation for the same. More than the answer, explanation carries more points in your solution.

Note: Use g++ 3.4 or higher compiler. Avoid using Turbo compilers. Do not use any optional flag for compilation.

Code

#include<iostream>
#include<limits>
using namespace std;
   
class Codefest {
    int a;
    int id[20000];       

    public:
    Codefest();
    Codefest(int);
    int& eventsCount();           
    void print();
    int& operator[](int);
     Codefest& operator=(const Codefest&);
};

Codefest::Codefest(){
    a=0;
    for(int i=0;i<20000;i++)
      id[i]=0;
}
Codefest::Codefest(int x){
    a=x;
    for(int i=0;i<20000;i++)
      id[i]=0;
   
}
int& Codefest::operator[](int x){
    return id[x];
}
 Codefest& Codefest::operator=(const Codefest& c){
    a=c.a;
    for(int i=0;i<20000;i++){
        id[i]=c.id[i];
    }
}
int& Codefest::eventsCount(){
    int ec=6;
    return ec;
}
void Codefest::print(){
    cout<<"Hello CodeWarriors"<<a<<endl;
}

int main(){
    Codefest* p2010 = NULL;
    p2010->print();
    p2010->eventsCount();
    Codefest c1;
    c1[0]=3;
    c1[1]=90;
    c1[2]=100;
    c1[3]=200;
    for(int i=0;i<4;i++){
        cout<<c1[i]<<endl;
    }
    return 0;
}

Solution

• To remove the warning, add a keyword static to line 39.
  static int ec = 6
  This is because whenever you are returning a reference you must be sure that the associated object exists even after returning from the function. Since locals get destroyed immediately after exit from function the returned reference must point to a static area which exists till the end of the program.
  Reference: Pg 452 Bruce Eckel Thinking in C++ Vol 1.
• To remove the run time error/segmentation fault, delete 3 characters from line 43.

  cout<<"Hello Warriors "<<endl;

  Though a "this" pointer is passed to every member function, that is not used until a member variable is accessed. Removing variable "a" from the line eliminates the null "this" pointer dereference , which was the reason for segmentation fault.
  Reference: Pg 240 Bruce Eckel Thinking in C++ Vol 1
• To get the desired output, change line 53 to
  c1 = 100
  This is an example of type conversion where the line has the same effect as
  c1 = Codefest(100);
  Constructors with single arguments also serve as type conversions. After this the "operator=" is invoked for the assignment and hence the new contents.
  Reference: http://www.cplusplus.com/doc/tutorial/typecasting/

  Post your queries regarding the solution at Debugging 2 Forum Thread.