Question

I learned that one of the motivation for copy constructor using is to avoid of the follow crash in the program –

#include <iostream>
using namespace std;

class Employee {
public:
    Employee(int ID,char const * name){...};
    ~Employee(){...};

    // Methods
    void Print();

private:
    // members
    int m_ID;
    char* m_name;
};

void MyFunc(Employee emp) {

    cout << "in MyFunc \n ";

}

int main() {
    Employee One(1,"Garen Torosian");

// calling copy constructor
    MyFunc(One);

    cout << "In the end of main \n";

// Here the program crashes!
    return 0;
}

as you can see the program should be crash before the return 0; , but when I run that program it works fine and terminated ok , why ?

Edit : In this case the program indeed crash –

// Employee.h
#include <iostream>
using namespace std;

class Employee {
public:
   Employee(int ID, 
                   const char* name);
  ~Employee();

  // Methods
  void Print();

private:
  // members
  int   m_ID;
  char* m_name;
};

---

// Employee.cpp
#include "Employee.h“

Employee::Employee(int iID, const char *name){ // Ctor
  cout << "Constructor called" << endl;
  m_ID = iID;
  m_name = new char [strlen(name) +1];
  strcpy(m_name, name);
  Print();
}
void Employee::Print() { // Print
cout << "ID: " << m_ID << ",Name:” << m_name
<< " ,Address(pointer):0x" << hex << (int) m_name<< endl;
}
Employee::~Employee() { // Dtor
  cout << "Destructor called"<<endl;
  Print();
  delete [] m_name;
  m_name=NULL;
}

---

void MyFunc(Employee emp) {

  cout << "in MyFunc \n ";    

}

int main()
{
    Employee One(1,"Eli Rachamim");

// calling copy constructor
MyFunc(One);

cout<< "In the end of main \n“;

// Here the program crashes! 
return 0;
}

Answer 1

If you d-tor is like

~Employee(){ delete[] name; }

and you alloc memory for your char* pointer, and you have no copy c-tor, than copy c-tor generated by compiler, that do memberwise-copy, will be called when you copy object. So, there will be double-free, that in most cases give you memory dump (in real calling destructor to already destructed object is UB and calling delete[] on already deleted object is also UB). But if you don’t work with memory – copy c-tor, generated by compiler works well.

EDIT.

So, your second example demonstrates call of d-tor to allready destructed object and also double-free.