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assignment & copy constructor

bluefrog (125)

I've created a class called StringBad based on chapter 11 of C++ Primer.
The purpose of the class is to experiment with the copy and assignment constructors:

I get a run time error whenever the following 2 lines of code are uncommented. 
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    // StringBad sailor = sports;
    // cout << "sailor: " << sailor << endl;


main is the following:
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#include <iostream>
using std::cout;
using std::endl;
#include "stringbad.h"

void callme1(StringBad &);
void callme2(StringBad);

int main() {
  {
    cout << "Starting an inner block.\n";
    StringBad headline1("Celery Stalks at Midnight");
    StringBad headline2("Lettuce Prey");
    StringBad sports("Spinach Leaves Bowl for Dollars");
    cout << "Headline1: " << headline1 << endl;
    cout << "Headline2: " << headline2 << endl;
    cout << "sports: : " << sports << endl;
    callme1(headline1);
    cout << "Headline1: " << headline1 << endl;
    callme2(headline2);
    cout << "Headline2: " << headline2 << endl;
    cout << "Initialise one object to another:\n";
    // StringBad sailor = sports;
    // cout << "sailor: " << sailor << endl;
    cout << "Assign one object to another:\n";
    StringBad knot;
    knot = headline1;
    cout << "knot: " << knot << endl;
    cout << "Exiting the block.\n";
  }
  return 0;
}
void callme1(StringBad & rsb) {
  cout << "String passed by reference: ";
  cout << "   \"" << rsb << "\"\n";
}
void callme2(StringBad sb) {
  cout << "String passed by value: ";
  cout << "   \"" << sb << "\"\n";
}

the class definition is :
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#include <iostream>
#include <cstring>
#include "stringbad.h"

int StringBad::num_strings = 0;

StringBad::StringBad(const char * s) {
  len = std::strlen(s);
  str = new char[len + 1];
  std::strcpy(str, s);
  num_strings++;
  std::cout << "\n" << num_strings << ": \"" << str << "\" object created\n"; 
}

StringBad::StringBad() {
  len = 4;
  str = new char[4];
  std::strcpy(str, "C++");
  num_strings++;
  std::cout << "\n" << num_strings << ": \"" << str << "\" default object created\n"; 
}

StringBad::~StringBad() {
  std::cout << "\n" << "\"" << str << "\" << object deleted, ";
  --num_strings;
  std::cout << "\n" << num_strings << " left\n";
  delete [] str;
}

StringBad::StringBad(const StringBad & s) {
  num_strings++;
  str = new char [len + 1];
  std::strcpy(str, s.str);
  len = s.len;
}

std::ostream & operator<<(std::ostream & os, const StringBad & st) {
  os << st.str;
  return os;
}

StringBad & StringBad::operator=(const StringBad & st) {
  if (this == &st)   // in case assigment occurs to self
    return *this;
  delete [] str;
  len = st.len;
  str = new char [len + 1];
  std::strcpy(str, st.str);
  return *this;
}

class declaration is:
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#ifndef STRBAD_H_
#define STRBAD_H_

#include <iostream>
// #include <string>

class StringBad {
  private:
    char * str;
    int len = 0;
    static int num_strings; 
  public:
    StringBad(const char *);
    StringBad(const StringBad & s);
    StringBad();
    ~StringBad();
    
    StringBad & operator=(const StringBad & st);
    friend std::ostream & operator<<(std::ostream & os, const StringBad & st);
};

#endif

Could anybody suggest why the runtime error? I use g++ 5.4 on ubuntu.
AbstractionAnon (6954)
stringbad.cpp line 32: len is 0. You want s.len (or move line 34 before line 32).
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