Use of sstream causing a deleted copy constructor

Question

So I am a CS student working on a project for exception handling (Try/catch). My teacher told us to implement the sstream library so we could use it in a class that outputs a message that includes a passed parameter of type int. For some reason unknown to me, when I use it, or even when I declare a variable of type stringstream, it causes a compile error with error message:

"copy constructor of 'tornadoException' is implicitly deleted because field 'ss' has a deleted copy constructor"

Here is my code. I am at a loss.

main.cpp

#include <iostream>
#include <string>
#include <sstream>
#include "tornadoException.h"

using namespace std;


int main() 
{
  try{
    int tornado = 0;
    cout << "Enter distance of tornado: ";
    cin >> tornado;
    
    if(tornado > 2){
      throw tornadoException(tornado);
    }
    else{
      throw tornadoException();
    }
  }
  catch(tornadoException tornadoObj){
    cout << tornadoObj.what();
  }
}

tornadoException.cpp

#include <iostream>
#include <string>
#include <sstream>

#include "tornadoException.h"

using namespace std;

  tornadoException::tornadoException(){
    message = "Tornado: Take cover immediately!";
  }

  tornadoException::tornadoException(int m){
    ss << "Tornado: " << m << "miles away!; and approaching!";
    message = ss.str();
 
  }

  string tornadoException::what(){
    return message;
  }

tornadoException.h

#ifndef tornadoException_h
#define tornadoException_h

#include <iostream>
#include <string>
#include <sstream>

using namespace std;

class tornadoException{
public:

  tornadoException();

  tornadoException(int m);

  string what();
private:
  stringstream ss;
  string message;
};

#endif

While this is true that `std::string_stream` doesn't have copy constructor, I bet your exception class does not need have a string stream as it's member! — SergeyA, Oct 21 '21 at 19:31
@SergeyA This was exactly right! Fixed the problem very swiftly after figuring this out. — jordanpaulee, Oct 21 '21 at 19:41

score 1 · Answer 1 · edited Oct 21 '21 at 20:01

1

stringstream has a deleted copy constructor, which means that a stringstream object cannot be copied.

Since your tornadoException class has a stringstream variable, this means that your class cannot be copied either.

In your main function, you capture the exception by value, which means that you are copying it into the tornadoObj variable - which is not allowed.

Try changing the line catch(tornadoException tornadoObj) to catch(tornadoException& tornadoObj) so that you're getting a reference to the exception instead of a copy of it.

This is actually a general rule: An exception shall always be caught by reference, not by copy: Core Guidelines E.15

edited Oct 21 '21 at 20:01

user4581301

33,082
7
33
54

answered Oct 21 '21 at 19:33

cptFracassa

893
4
14

1

In general one should catch exceptions not by reference, but by *const reference* (`const &`). – Jesper Juhl Oct 21 '21 at 19:55
@JesperJuhl You are right of course. – cptFracassa Oct 22 '21 at 11:15

score 1 · Answer 2 · answered Oct 21 '21 at 19:36

Alright, figured out the error but I'll leave up this post since I couldn't find the answer anywhere else. The problem was that I declared the stringstream buffer as a private variable in the class. The buffer needs to be declared locally within the function declaration it is being used in, in this case right before the loading of the buffer in the implementation file:

tornadoException::tornadoException(int m){
stringstream ss;
ss << "Tornado: " << m << " miles away!; and approaching!";
message = ss.str();
}

Use of sstream causing a deleted copy constructor

2 Answers2