segmentation when cout

[madshov]

Hi,

I'm trying to overload the << operator. I have a point class which is represented by a vector of doubles. In this class I have overloaded the << operator with no problem:

class Point
{
  public:
    //constructor
    Point();
    Point(vector<double> v);
}
 
Point::Point()
{
   vector<double> vec(4,0);
   vec[3]= 1;
   point = vec;
   size  = vec.size();
}
 

ostream& operator<<(ostream& os, const Point& p) 
{
   int sz = p.get_size();
   os << "(";
   for (int i=0; i<sz; i++) {
      os << p.get_val(i) << " ";
   }
   os << ")" << endl;
   return os;
}

Now I have created another class, which instantiates 4 points of class Point:

fourpoints::fourpoints()
{
    Point p1;
    Point p2;
    Point p3;
    Point p4;
}

When I try to overload the << operator here I get a segmentation fault:

ostream& operator<<(ostream& os, const fourpoints& p) 
{
   os << "1. point: " << p.get_1();
   return os;
}

The function get_1() just returns the first point:

Point fourpoint::get_1() const
{
    return this->p1;
}

Can anybody tell what I'm doing wrong? It fails when I try to print the coordinate in the point. The output is "1. point: (" and nothing more

[weaknessforcats]

fourpoints::fourpoints()
{
Point p1;
Point p2;
Point p3;
Point p4;
}

These Point variables are local to this constructor. They will be destroyed when the constructor completes.

You didn't post your fourpoints class so I can't see what is decared there.

[madshov]

The fourpoints class:

class fourpoints
{ 
    public:
 
    //constructor
    fourpoints();
 
    //destructor
    ~fourpoints();
 
    Point fourpoints::get_1() const;
    friend ostream& operator<<(ostream& os, const fourpoints& p);
 
    private:
    Point p1, p2, p3, p4;
};

[weaknessforcats]

Point::Point()
{
vector<double> vec(4,0);
vec[3]= 1;
point = vec;
size = vec.size();
}

Your vector vec is local to the Point constructor. It will be destroyed when the constrcutor completes.

This is the second place you have done this. Your data members belong in the class as private members and not as local variables in your funcitons.

Also, vec[3] will fail becuse there is no element there. You need to put elements in the vector before you can assign to them.

Also, vector<double> vec(4,0) won't compile on my system.

Also, point and size are not defined so these lines won't compile either.


I suggest you fix your code so it compiles and post again.

[mschenkelberg]

Your vector vec is local to the Point constructor. It will be destroyed when the constrcutor completes.

This is the second place you have done this. Your data members belong in the class as private members and not as local variables in your funcitons.

Also, vec[3] will fail becuse there is no element there. You need to put elements in the vector before you can assign to them.

Also, vector<double> vec(4,0) won't compile on my system.

Also, point and size are not defined so these lines won't compile either.


I suggest you fix your code so it compiles and post again.

The two parameter constructor is defined here: http://cppreference.com/cppvector/vector_constructors.html

If you left out any code post it.

Max

[madshov]

Hi,
Sorry, I only pasted some parts of my code, but I found the reason for the problem myself.